Filed Pursuant to Rule 424(b)(5)
Registration No. 333-224017

CALCULATION OF REGISTRATION FEE

Prospectus Supplement

(To Prospectus dated March 29, 2018)

$5,000,000,000

Merck & Co., Inc.

$750,000,000 2.900% Notes due 2024

$1,750,000,000 3.400% Notes due 2029

$1,000,000,000 3.900% Notes due 2039

$1,500,000,000 4.000% Notes due 2049

We are offering $750,000,000 aggregate principal amount of our 2.900% Notes due 2024 (the “2024 notes”), $1,750,000,000 aggregate principal amount of our 3.400% Notes due 2029 (the “2029 notes”), $1,000,000,000 aggregate principal amount of our 3.900% Notes due 2039 (the “2039 notes”) and $1,500,000,000 aggregate principal amount of our 4.000% Notes due 2049 (the “2049 notes”). We refer to the 2024 notes, the 2029 notes, the 2039 notes and the 2049 notes collectively as the “notes.”

Interest on the notes is payable on March 7 and September 7 of each year, beginning on September 7, 2019. The 2024 notes will mature on March 7, 2024, the 2029 notes will mature on March 7, 2029, the 2039 notes will mature on March 7, 2039 and the 2049 notes will mature on March 7, 2049.

We may redeem some or all of the notes of each series at any time at the applicable redemption price set forth in this prospectus supplement under the caption “Description of the Notes—Optional Redemption.”

The notes will be our unsecured senior debt obligations and will rank equally with all of our other unsecured senior indebtedness from time to time outstanding. The notes will be issued only in denominations of $2,000 and integral multiples of $1,000 in excess thereof. The notes will not be convertible or exchangeable.

Investing in the notes involves risks. See “Risk Factors” beginning on page S-2 of this prospectus supplement and in the documents incorporated by reference in this prospectus supplement and the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Interest on the notes will accrue from March 7, 2019. The notes will not be listed on any securities exchange or automated dealer quotation system. Currently, there is no public market for the notes.

We expect that delivery of the notes will be made to investors in book-entry form only through the facilities of The Depository Trust Company and its participants, including Clearstream Banking S.A. and Euroclear Bank S.A./N.V., on or about March 7, 2019.

Joint Book-Running Managers

Citigroup

Co-Managers

March 5, 2019

We have not, and the underwriters have not, authorized anyone to provide you with any information other than that contained or incorporated by reference in this prospectus supplement, any related free writing prospectus prepared by us or the accompanying prospectus. We take no responsibility for, and can provide no assurance as to the reliability of any other information that others may give you. If the information varies between this prospectus supplement and the accompanying prospectus, the information in this prospectus supplement supersedes the information in the accompanying prospectus. We are not making an offer of these securities in any jurisdiction where the offer or sale is not permitted. Neither the delivery of this prospectus supplement, any related free writing prospectus or the accompanying prospectus, nor any sale made hereunder and thereunder, shall under any circumstances create any implication that there has been no change in our affairs since the date of this prospectus supplement, any related free writing prospectus or the accompanying prospectus, regardless of the time of delivery of such document or any sale of the securities offered hereby and thereby, or that the information contained or incorporated by reference herein or therein is correct as of any time subsequent to the date of such information. Unless the context requires otherwise, references to the “prospectus” in this prospectus supplement and the accompanying prospectus mean both this prospectus supplement and the accompanying prospectus combined.

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TABLE OF CONTENTS

Prospectus Supplement

Prospectus

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MERCK

We are a global health care company that delivers innovative health solutions through our prescription medicines, vaccines, biologic therapies and animal health products. Our operations are principally managed on a products basis and include four operating segments, which are the Pharmaceutical, Animal Health, Healthcare Services and Alliances segments.

The Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. We sell these human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies and managed health care providers such as health maintenance organizations, pharmacy benefit managers and other institutions. Human health vaccine products consist of preventive pediatric, adolescent and adult vaccines, primarily administered at physician offices. We sell these human health vaccines primarily to physicians, wholesalers, physician distributors and government entities.

The Animal Health segment discovers, develops, manufactures and markets animal health products, including pharmaceutical and vaccine products, for the prevention, treatment and control of disease in all major livestock and companion animal species, which we sell to veterinarians, distributors and animal producers.

The Healthcare Services segment provides services and solutions that focus on engagement, health analytics and clinical services to improve the value of care delivered to patients.

The Alliances segment primarily includes results from our relationship with AstraZeneca LP related to sales of Nexium and Prilosec, which concluded in 2018.

We were incorporated in New Jersey in 1970 and maintain our principal offices in Kenilworth, New Jersey. Our address is 2000 Galloping Hill Road, Kenilworth, New Jersey 07033, and our telephone number is (908) 740-4000. Our website is located at www.merck.com. Information available on, or accessible through, our website is not incorporated into this prospectus supplement or the accompanying prospectus by reference and should not be considered a part of this prospectus supplement or the accompanying prospectus.

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RISK FACTORS

Before acquiring any of the notes, you should carefully consider the following risk factors and the risk factors and assumptions related to us identified or described in our Annual Report on Form 10-K for the year ended December 31, 2018 incorporated by reference herein, and all other information contained or incorporated by reference into this prospectus supplement and the accompanying prospectus. The occurrence of any one or more of the foregoing or following risks could materially adversely affect your investment in the notes or our business, financial condition, results of operations or prospects.

The notes are obligations exclusively of Merck and not of our subsidiaries, and payment to holders of the notes will be structurally subordinated to the liabilities of our subsidiaries.

The notes are not guaranteed by any of our subsidiaries and therefore the notes will be structurally subordinated to all existing and future secured and unsecured indebtedness and other liabilities of our subsidiaries. The indebtedness of our subsidiaries totaled $1.7 billion as of December 31, 2018, substantially all of which we have guaranteed. The notes will be structurally subordinated to our subsidiaries’ obligations with respect to that indebtedness, and our guarantee of that indebtedness will rank pari passu with the notes. In addition, our obligations under the notes will be structurally subordinated to guarantees by our subsidiaries of our indebtedness. As of December 31, 2018, certain of our subsidiaries also guaranteed $1.0 billion aggregate principal amount of our existing indebtedness. The terms of the notes and the indenture do not preclude our subsidiaries from incurring debt or other liabilities or providing guarantees that will be structurally senior to the notes.

The notes are our unsecured obligations and will be effectively junior to secured indebtedness that we may incur or issue.

The notes will be unsecured obligations. Holders of any secured debt that we may incur or issue may foreclose on the assets securing such debt, reducing the cash flow from the foreclosed property available for payment of unsecured debt, including the notes. Holders of our secured debt also would have priority over unsecured creditors in the event of our bankruptcy, liquidation or similar proceeding. In the event of our bankruptcy, liquidation or similar proceeding, holders of our secured debt would be entitled to proceed against their collateral, and the assets securing that collateral may not be available for payment of unsecured debt, including the notes. As a result, the notes will be effectively junior to any secured debt that we may incur or issue, to the extent of the value of the assets securing such debt.

Active trading markets for the notes may not develop, which could limit their market prices or your ability to sell them.

The notes are new issues of debt securities for which there currently are no trading markets. As a result, we cannot provide any assurance that any markets will develop for the notes or that you will be able to sell your notes. We have no plans to list the notes on any securities exchange or to arrange for quotation on any automated dealer quotation system. If any of the notes are traded after their initial issuance, they may trade at discounts from their initial offering prices depending on prevailing interest rates, the markets for similar securities, general economic conditions, our financial condition, performance and prospects and other factors. The underwriters have advised us that they intend to make a market in each series of notes, but they are not obligated to do so. The underwriters may discontinue any market-making in the notes at any time at their sole discretion. Accordingly, we cannot assure you that a liquid trading market will develop for the notes of any series, that you will be able to sell your notes at a particular time or that the prices you receive when you sell will be favorable. To the extent active trading markets do not develop, the liquidity and trading prices for the notes may be harmed. Accordingly, you may be required to bear the financial risk of an investment in the notes for an indefinite period of time.

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FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus and any documents we incorporate by reference herein or therein and oral statements made from time to time by us may contain so called “forward-looking statements” (within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act), all of which are based on management’s current expectations and are subject to risks and uncertainties which may cause results to differ materially from those set forth in the statements. All statements that do not relate strictly to historical or current facts are forward-looking statements. One can generally identify these forward-looking statements by their use of words such as “anticipates,” “expects,” “plans,” “will,” “estimates,” “forecasts,” “projects” and other words of similar meaning, or negative variations of any of the foregoing. Forward-looking statements include statements about our growth strategy, future financial results, new product development, pending or upcoming product approvals, product potential and development programs. One must carefully consider any such statement and should understand that many factors could cause actual results to differ materially from our forward-looking statements. These factors include assumptions and a broad variety of other known and unknown risks and uncertainties. No forward-looking statement can be guaranteed. We do not assume the obligation to update any forward-looking statement. We caution you not to place undue reliance on these forward-looking statements. Although it is not possible to predict or identify all such factors, important factors that could cause actual results to differ materially from those in the forward-looking statements include the following:

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This list should not be considered an exhaustive statement of all potential risks and uncertainties. See “Risk Factors” above as well as the risk factors described in the documents incorporated herein by reference.

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USE OF PROCEEDS

The net proceeds of the offering after giving effect to the underwriting discounts and other offering expenses are estimated to be approximately $4.92 billion. We intend to use the net proceeds of the offering for general corporate purposes, including without limitation the repayment of outstanding commercial paper borrowings and other indebtedness with upcoming maturities.

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CAPITALIZATION

The following table sets forth the consolidated capitalization of Merck and its subsidiaries at December 31, 2018 on a historical basis and as adjusted to reflect the issuance and sale of the notes.

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DESCRIPTION OF THE NOTES

The following description of the particular terms of the 2024 notes, the 2029 notes, the 2039 notes and the 2049 notes offered hereby supplements the general description of debt securities set forth in the accompanying prospectus under “Description of Debt Securities We May Offer.” References to the “notes” refer to the 2024 notes, the 2029 notes, the 2039 notes and the 2049 notes, collectively. We qualify the description of the notes by reference to the indenture as described below. The 2024 notes, the 2029 notes, the 2039 notes and the 2049 notes will each be issued as a separate series of debt securities under the indenture.

The 2024 notes will initially be limited to $750,000,000 aggregate principal amount and will mature on March 7, 2024. The 2029 notes will initially be limited to $1,750,000,000 aggregate principal amount and will mature on March 7, 2029. The 2039 notes will initially be limited to $1,000,000,000 aggregate principal amount and will mature on March 7, 2039. The 2049 notes will initially be limited to $1,500,000,000 aggregate principal amount and will mature on March 7, 2049.

The notes are unsecured and will rank equally with all our other unsecured and unsubordinated indebtedness from time to time outstanding. The notes will not be guaranteed by any of our subsidiaries and will therefore be structurally subordinated to all liabilities of our subsidiaries from time to time outstanding, including any guarantees provided by our subsidiaries. As of December 31, 2018, the indebtedness of our subsidiaries totaled $1.7 billion and certain of our subsidiaries also guaranteed $1.0 billion aggregate principal amount of our indebtedness.

We will issue the notes under the indenture, dated as of January 6, 2010 (the “base indenture”) between us and U.S. Bank Trust National Association, as trustee (the “trustee”), as supplemented with respect to each series of notes by an officers’ certificate establishing the terms thereof. In this description of the notes, the term “indenture” refers to the base indenture as supplemented separately by the officers’ certificate for each series of notes. The terms of the notes of each series include those stated in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as amended.

The notes will be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

The full defeasance and covenant defeasance provisions of the indenture described under “Description of Debt Securities We May Offer—Defeasance” in the accompanying prospectus will apply to the notes.

Interest

The notes will bear interest from March 7, 2019.

The 2024 notes will bear interest at a rate of 2.900% per annum, the 2029 notes will bear interest at a rate of 3.400% per annum, the 2039 notes will bear interest at a rate of 3.900% per annum and the 2049 notes will bear interest at a rate of 4.000% per annum. Interest on the notes will be payable semi-annually in arrears on March 7 and September 7 of each year, commencing on September 7, 2019, to the person in whose name such notes were registered at the close of business on the preceding February 20 or August 23, as the case may be. Interest on the notes will be computed on the basis of a 360-day year composed of twelve 30-day months. If any payment date for the notes is not a business day, we will make the payment on the next business day, but we will not be liable for any additional interest as a result of the delay in payment. With respect to the notes, by business day, we mean any Monday, Tuesday, Wednesday, Thursday or Friday which is not a day when banking institutions in the place of payment are authorized or obligated by law or executive order to be closed.

Optional Redemption

We may, at our option, redeem some or all of the 2024 notes, the 2029 notes, the 2039 notes or the 2049 notes prior to the applicable Par Call Date (as defined below) at any time or from time to time, at a redemption price equal to the greater of (i) 100% of the principal amount of the notes to be redeemed or (ii) the sum of the

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present values of the Remaining Scheduled Payments (as defined below) discounted to the redemption date on a semiannual basis (assuming a 360-day year consisting of twelve 30-day months) at a rate equal to the Reinvestment Rate (as defined below) plus 10 basis points with respect to the 2024 notes, the Reinvestment Rate plus 12.5 basis points with respect to the 2029 notes, the Reinvestment Rate plus 15 basis points with respect to the 2039 notes and the Reinvestment Rate plus 15 basis points with respect to the 2049 notes, plus, in each case, any interest accrued but not paid to the date of redemption.

We may redeem the 2024 notes, the 2029 notes, the 2039 notes or the 2049 notes, on or after the Par Call Date, in whole, or from time to time in part, at a redemption price equal to 100% of the principal amount of the 2024 notes, the 2029 notes, the 2039 notes or the 2049 notes, as applicable, plus any interest accrued but not paid to the date of redemption.

Notice of redemption will be provided on at least 30 days’, but no more than 60 days’, prior notice to the holders of that series of notes. The principal amount of a note remaining outstanding after a redemption in part shall be $2,000 or an integral multiple of $1,000 in excess thereof.

The term “Par Call Date” means February 7, 2024, the date that is one month prior to the maturity of the 2024 notes, December 7, 2028, the date that is three months prior to the maturity of the 2029 notes, September 7, 2038, the date that is six months prior to the maturity of the 2039 notes and September 7, 2048, the date that is six months prior to the maturity of the 2049 notes.

The “Reinvestment Rate” means, as determined on the third business day preceding the date the notice of redemption is provided, the arithmetic mean of the yields under the respective heading “Week Ending” published in the most recent Statistical Release (as defined below) under the caption “Treasury Constant Maturities” for the maturity, rounded to the nearest month, corresponding to the remaining life to the applicable Par Call Date, as of the payment date of the principal being redeemed or paid. If no maturity exactly corresponds to such remaining life to the applicable Par Call Date, yields for the two published maturities most closely corresponding to such remaining life to the applicable Par Call Date shall be calculated pursuant to the immediately preceding sentence and the Reinvestment Rate shall be interpolated or extrapolated from such yields on a straight-line basis, rounding in each of such relevant periods to the nearest month. For the purpose of calculating the Reinvestment Rate, the most recent Statistical Release published prior to the date of determination shall be used. If the format or content of the Statistical Release changes in a manner that precludes determination of the treasury yield in the above manner, then the treasury yield shall be determined in the manner that most closely approximates the above manner, as reasonably determined by us in consultation with the trustee.

“Remaining Scheduled Payments” means, with respect to each 2024 note, 2029 note, 2039 note and 2049 note to be redeemed, the remaining scheduled payments of principal and interest that would be due after the related redemption date but for the redemption if such series of notes matured on the applicable Par Call Date. If the redemption date is not an interest payment date with respect to a note, the amount of the next succeeding scheduled interest payment on the note will be reduced by the amount of interest accrued on the note to the redemption date.

“Statistical Release” means the statistical release designated “H.15 (519)” or any successor publication which is published weekly by the Federal Reserve System and which reports yields on actively traded United States government securities adjusted to constant maturities, or, if such statistical release is not published at the time of any determination, then such other reasonably comparable index which shall be designated by us.

If fewer than all of the notes of any series are to be redeemed, the trustee will select the particular notes or portions thereof for redemption from the outstanding notes not previously called, pro rata or by lot, or in such other manner as we will direct.

Unless we default in payment of the redemption price, on and after the redemption date interest will cease to accrue on the notes or portions thereof called for redemption.

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Further Issues

We may, without the consent of holders of any series of notes offered by this prospectus supplement, issue additional notes having the same ranking and the same interest rate, maturity and other terms as the notes of that series. Any additional notes of any series, together with the outstanding notes of the applicable series, will constitute a single series of notes under the indenture. No additional notes may be issued if an event of default has occurred and is continuing with respect to the applicable series of notes. Additional notes cannot be issued under the same CUSIP number unless the additional notes and original notes are fungible for U.S. federal income tax purposes.

Book-Entry System

Upon issuance, the notes of each series will be represented by one or more global notes. Each global note will be deposited with, or on behalf of, The Depository Trust Company, as depository, and registered in the name of a nominee of the depository.

Investors may elect to hold interests in the global notes held by the depository through Clearstream Banking, S.A. (“Clearstream, Luxembourg”) or Euroclear Bank S.A./N.V., as operator of the Euroclear System (the “Euroclear operator”) if they are participants of such systems, or indirectly through organizations that are participants in such systems. Clearstream, Luxembourg and the Euroclear operator will hold interests on behalf of their participants through customers’ securities accounts in Clearstream, Luxembourg’s and the Euroclear operator’s names on the books of their respective depositories, which in turn will hold such interests in customers’ securities accounts in the depositories’ names on the books of the depository. Citibank, N.A. will act as depository for Clearstream, Luxembourg, and JPMorgan Chase Bank will act as depository for the Euroclear operator (in such capacities, the “U.S. depositories.”) Because holders will acquire, hold and transfer security entitlements with respect to the notes through accounts with DTC and its participants, including Clearstream, Luxembourg, the Euroclear operator and their participants, a beneficial holder’s rights with respect to the notes will be subject to the laws (including Article 8 of the Uniform Commercial Code) and contractual provisions governing a holder’s relationship with its securities intermediary and the relationship between its securities intermediary and each other securities intermediary and between it and us, as the issuer. Except as set forth below, the global notes may be transferred, in whole and not in part, only to another nominee of the depository or to a successor of the depository or its nominee.

Ownership of beneficial interests in a global note will be limited to institutions that have accounts with the depository or its nominee or persons that may hold interests through participants. We have been advised by the depository that upon receipt of any payment of principal of, or interest on, a global note, the depository will credit, on its book-entry registration and transfer system, accounts of participants with payments in amounts proportionate to their respective beneficial interests in the principal amount of the global notes as shown on the records of the depository. Ownership of beneficial interests by participants in the global note will be evidenced only by, and the transfer of that ownership interest will be effected only through, records maintained by the depository or its nominee. Ownership of beneficial interests in the global note by persons that hold through participants will be evidenced only by, and the transfer of that ownership interest within such participant will be effected only through, records maintained by participants. The laws of some jurisdictions require that certain purchasers of securities take physical delivery of such securities in definitive form. These laws may impair the ability to transfer beneficial interests in the global note.

Payment of principal of, and interest on, any global note registered in the name of or held by the depository or its nominee will be made to the depository or its nominee, as the case may be, as the registered owner of the global note. Payments by participants to owners of beneficial interests in a global note held through the participants will be governed by standing instructions and customary practices, as is now the case with securities held for the accounts of customers registered in “street name,” and will be the sole responsibility of the participants. None of us, the trustee, the underwriters, nor any agent of ours or the trustee will have any

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responsibility or liability for any aspects of the depository’s records or any participant’s records relating to, or payments made on account of, beneficial ownership interests in a global note or for maintaining, supervising or reviewing any of the depository’s records or any participant’s records relating to the beneficial ownership interests.

No global note may be transferred except as a whole by the depository to a nominee of the depository or by a nominee of the depository to the depository or another nominee of the depository.

No global note may be exchanged in whole or in part for notes registered, and no transfer of a global note in whole or in part may be registered, in the name of any person other than the depository or any nominee of the depository unless (i) the depository has notified us that it is unwilling or unable to continue as depository for such global note or has ceased to be qualified to act as such as required by the indenture, (ii) there has occurred and is continuing an event of default with respect to the notes or (iii) we determine in our sole discretion at any time that the global note shall be so exchangeable.

Any global note that is exchangeable pursuant to the preceding sentence shall be exchangeable in whole for separate notes in registered form of any authorized denomination and of like tenor and aggregate principal amount. These notes shall be registered in the name or names of such person or persons as the depository instructs the trustee. We expect that these instructions would be based upon directions received by the depository from its participants with respect to ownership of beneficial interests in such global note.

As long as the depository, or its nominee, is the registered holder of a note, the depository or such nominee, as the case may be, will be considered the sole owner and holder of such global note for all purposes under the notes and the indenture. Except in the limited circumstances referred to above, owners of beneficial interests in a global note will not be entitled to have such global note registered in their names, will not receive or be entitled to receive physical delivery of notes in exchange therefor and will not be considered to be the owners or holders of such global note for any purpose under the notes or the indenture. Accordingly, each person owning a beneficial interest in the global note must rely on the procedures of the participant through which such person owns its interest to exercise any rights of a holder under the indenture.

The indenture provides that the depository, as a holder, may appoint agents and otherwise authorize participants to give or take any request, demand, authorization, direction, notice, consent, waiver, or other action which a holder is entitled to give or take under the indenture.

The depository has advised us as follows: the depository is a limited-purpose trust company organized under the New York Banking Law, a “banking organization” within the meaning of the New York Banking Law, a member of the Federal Reserve System, a “clearing corporation” within the meaning of the New York Uniform Commercial Code, and a “clearing agency” registered pursuant to the provisions of Section 17A of the Exchange Act. The depository was created to hold securities of its participants and to facilitate the clearance and settlement of securities transactions, such as transfers and pledges, among its participants in these securities through electronic computerized book-entry changes in accounts of the participants, thereby eliminating the need for physical movement of securities certificates. The depository’s participants include securities brokers and dealers, banks, trust companies, clearing corporations and other organizations, some of whom (and/or their representatives) own the depository. Access to the depository’s book-entry system is also available to others, such as banks, brokers, dealers and trust companies, that clear through or maintain a custodial relationship with a participant, either directly or indirectly.

Clearstream, Luxembourg advises that it is a limited liability company organized under Luxembourg law. Clearstream, Luxembourg holds securities for its participating organizations (“Clearstream, Luxembourg participants”) and facilitates the clearance and settlement of securities transactions between Clearstream, Luxembourg participants through electronic book-entry transfers between their accounts, thereby eliminating the need for physical movement of securities. Clearstream, Luxembourg provides to Clearstream, Luxembourg

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participants, among other things, services for safekeeping, administration, clearance and settlement of internationally traded securities and securities lending and borrowing. Clearstream, Luxembourg interfaces with domestic securities markets in several countries through established depository and custodial relationships. Clearstream, Luxembourg is registered as a bank in Luxembourg, and as such is subject to regulation by the Luxembourg Commission for the Supervision of the Financial Sector (Commission de Surveillance du Secteur Financier). Clearstream, Luxembourg participants are world-wide financial institutions, including underwriters, securities brokers and dealers, banks, trust companies and clearing corporations. Clearstream, Luxembourg’s U.S. customers are limited to securities brokers and dealers and banks. Indirect access to Clearstream, Luxembourg is also available to other institutions such as banks, brokers, dealers and trust companies that clear through or maintain a custodial relationship with a Clearstream, Luxembourg customer. Clearstream, Luxembourg has established an electronic bridge with the Euroclear operator to facilitate settlement of trades between Clearstream, Luxembourg and the Euroclear operator.

Distributions with respect to the notes held beneficially through Clearstream, Luxembourg will be credited to cash accounts of Clearstream, Luxembourg participants in accordance with its rules and procedures, to the extent received by the U.S. depository for Clearstream, Luxembourg.

The Euroclear operator advises that the Euroclear System was created in 1968 to hold securities for its participants (“Euroclear participants”) and to clear and settle transactions between Euroclear participants through simultaneous electronic book-entry delivery against payment, thereby eliminating the need for physical movement of certificates and any risk from lack of simultaneous transfers of securities and cash. The Euroclear System is operated by Euroclear Bank S.A./N.V. (the “Euroclear operator”) under contract with Euroclear Clearance Systems S.C., a Belgian cooperative corporation. The Euroclear operator is regulated and examined by the Belgian Banking and Finance Commission and the National Bank of Belgium. All operations are conducted by the Euroclear operator, and all Euroclear securities clearance accounts and Euroclear cash accounts are accounts with the Euroclear operator, not the cooperative. The cooperative establishes policy for Euroclear on behalf of Euroclear participants. Euroclear participants include banks, securities brokers and dealers and other professional financial intermediaries and may include the underwriters. Indirect access to Euroclear is also available to other firms that clear through or maintain a custodial relationship with a Euroclear participant, either directly or indirectly.

Securities clearance accounts and cash accounts with the Euroclear operator are governed by the Terms and Conditions Governing Use of Euroclear and the related Operating Procedures of the Euroclear System, and applicable Belgian law (collectively, the “terms and conditions.”) The terms and conditions govern transfers of securities and cash within the Euroclear System, withdrawals of securities and cash from the Euroclear System, and receipts of payments with respect to securities in the Euroclear System. All securities in the Euroclear System are held on a fungible basis without attribution of specific certificates to specific securities clearance accounts. The Euroclear operator acts under the terms and conditions only on behalf of Euroclear participants and has no record of or relationship with persons holding through Euroclear participants.

Distributions with respect to the notes held beneficially through the Euroclear System will be credited to the cash accounts of Euroclear participants in accordance with the terms and conditions, to the extent received by the U.S. depository for the Euroclear operator.

Title to book-entry interests in the notes will pass by book-entry registration of the transfer within the records of Clearstream, Luxembourg, the Euroclear operator or the depository, as the case may be, in accordance with their respective procedures. Book-entry interests in the notes may be transferred within Clearstream, Luxembourg and within the Euroclear System and between Clearstream, Luxembourg and the Euroclear System in accordance with procedures established for these purposes by Clearstream, Luxembourg and the Euroclear operator. Book-entry interests in the notes may be transferred within the depository in accordance with procedures established for this purpose by the depository. Transfers of book-entry interests in the notes among Clearstream, Luxembourg and the Euroclear operator and the depository may be effected in accordance with procedures established for this purpose by Clearstream, Luxembourg, the Euroclear operator and the depository.

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Secondary market trading between Clearstream, Luxembourg participants and/or Euroclear participants will occur in the ordinary way in accordance with the applicable rules and operating procedures of Clearstream, Luxembourg and the Euroclear System and will be settled using the procedures applicable to conventional Eurobonds in immediately available funds.

Cross-market transfers between persons holding directly or indirectly through the depository on the one hand, and directly or indirectly through Clearstream, Luxembourg participants or Euroclear participants, on the other, will be effected through the depository in accordance with the depository’s rules on behalf of the relevant European international clearing system by its U.S. depository; however, these cross-market transactions will require delivery of instructions to the relevant European international clearing system by the counterparty in the clearing system in accordance with its rules and procedures and within its established deadlines (European time). The relevant European international clearing system will, if the transaction meets its settlement requirements, deliver instructions to its U.S. depository to take action to effect final settlement on its behalf by delivering interests in the notes to or receiving interests in the notes from the depository, and making or receiving payment in accordance with normal procedures for same-day funds settlement applicable to the depository. Clearstream, Luxembourg participants and Euroclear participants may not deliver instructions directly to their respective U.S. depositories.

Because of time-zone differences, credits of interests in the notes received in Clearstream, Luxembourg or the Euroclear system as a result of a transaction with a depository participant will be made during subsequent securities settlement processing and dated the business day following the depository settlement date. Credits of interests or any transactions involving interests in the notes received in Clearstream, Luxembourg or the Euroclear System as a result of a transaction with a depository participant and settled during subsequent securities settlement processing will be reported to the relevant Clearstream, Luxembourg participants or Euroclear participants on the business day following the depository settlement date. Cash received in Clearstream, Luxembourg or the Euroclear System as a result of sales of interests in the notes by or through a Clearstream, Luxembourg customer or a Euroclear participant to a depository participant will be received with value on the depository settlement date but will be available in the relevant Clearstream, Luxembourg or Euroclear cash account only as of the business day following settlement in the depository.

Although the depository, Clearstream, Luxembourg and the Euroclear operator have agreed to the foregoing procedures in order to facilitate transfers of interests in the notes among participants of the depository, Clearstream, Luxembourg and Euroclear, they are under no obligation to perform or continue to perform the foregoing procedures and these procedures may be changed or discontinued at any time.

Governing Law

The indenture and the notes will be governed by, and construed and enforced in accordance with, the laws of the State of New York applicable to agreements made or instruments entered into and performed in New York State.

Open Market Purchases

We may at any time and from time to time purchase notes in the open market or otherwise.

The Trustee, Paying Agent and Security Registrar

U.S. Bank Trust National Association is the trustee, paying agent and security registrar with respect to the notes. U.S. Bank Trust National Association currently serves as the trustee with respect to certain of our other outstanding debt securities.

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CERTAIN U.S. FEDERAL TAX CONSEQUENCES

The following summary describes certain U.S. federal income tax consequences and, in the case of a non-U.S. Holder (as defined below), certain U.S. federal estate tax consequences, of purchasing, owning and disposing of the notes. This summary does not discuss all of the aspects of U.S. federal income and estate taxation that may be relevant to you in light of your particular investment or other circumstances. This summary applies to you only if you are a beneficial owner of a note that holds the note as a capital asset (generally, investment property), and you acquire the note for cash in this offering for a price equal to the issue price of the notes of the applicable series (i.e., the first price at which a substantial amount of the notes of the applicable series is sold for money to investors, other than to bond houses, brokers, or similar persons or organizations acting in the capacity of underwriters, placement agents or wholesalers). In addition, this summary does not address special U.S. federal income or estate tax rules that may be applicable to certain categories of beneficial owners of notes, such as:

In the case of an entity or arrangement classified as a partnership for U.S. federal tax purposes, the U.S. federal income tax treatment of a partner in the partnership generally will depend on the status of the partner, the activities of the partnership and certain determinations made at the partner level. If you are a partnership considering purchasing notes, or a partner in such a partnership, you should consult your own tax advisor regarding the U.S. federal income and estate tax consequences of purchasing, owning and disposing of the notes.

This summary is based on U.S. federal income and estate tax law, including the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), Treasury regulations, administrative rulings and judicial authorities, all as in effect or in existence as of the date of this prospectus supplement. Subsequent developments in U.S. federal income and estate tax law, including changes in law or differing interpretations, which may be applied retroactively, could have a material effect on the U.S. federal income and estate tax consequences of purchasing, owning and disposing of notes as set forth in this summary. We cannot assure you that the Internal Revenue Service (the “IRS”) will not challenge one or more of the tax consequences described in this summary, and we have not obtained, nor do we intend to obtain, any ruling from the IRS or opinion of counsel with respect to the tax consequences of the purchase, ownership or disposition of the notes. In addition, this summary does not discuss any U.S. federal tax consequences other than U.S. federal income tax consequences (and, in the case of non-U.S. Holders, U.S. federal estate tax consequences), such as gift tax consequences or the Medicare tax on certain investment income, or any U.S. state or local income or non-U.S. income or other tax consequences.

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U.S. Holders that use an accrual method of accounting for U.S. federal income tax purposes generally are required to include certain amounts in income no later than the time such amounts are reflected on certain applicable financial statements. The application of this rule may require the accrual of income earlier than would be the case under the general U.S. federal income tax rules described below, although it is not clear to what types of income this rule applies. If you are a U.S. Holder that uses an accrual method of accounting for U.S. federal income tax purposes, you should consult with your tax advisor regarding the potential applicability of this rule to your particular situation.

Before you purchase notes, you should consult your own tax advisor regarding the particular U.S. federal, state and local and non-U.S. income and other tax consequences of acquiring, owning and disposing of the notes that may be applicable to you.

U.S. Holders

The following summary applies to you only if you are a U.S. Holder (as defined below). A “U.S. Holder” is a beneficial owner of a note or notes that is for U.S. federal income tax purposes:

Payments of Stated Interest

Stated interest on your notes will be taxed as ordinary interest income. In addition:

Sale or Other Taxable Disposition of Notes

Upon the sale, redemption, retirement, exchange or other taxable disposition of the notes, you generally will recognize taxable gain or loss equal to the difference, if any, between:

Your tax basis in your notes generally will be their cost.

Your gain or loss generally will be capital gain or loss. This capital gain or loss will be long-term capital gain or loss if, at the time of the disposition, you have held the notes for more than one year. Subject to limited exceptions, your capital losses cannot be used to offset your ordinary income. If you are a non-corporate U.S. Holder, under current law your long-term capital gain generally will be subject to a preferential rate of U.S. federal income tax.

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Information Reporting and Backup Withholding

In general, information reporting requirements may apply to payments to a U.S. Holder of stated interest on the notes and the proceeds of a sale or other disposition (including a retirement or redemption) of the notes.

In general, “backup withholding” (currently at a rate of 24%) may apply:

if you are a U.S. Holder and you fail to provide a correct taxpayer identification number or otherwise comply with applicable requirements of the backup withholding rules and you do not otherwise establish an exemption.

Backup withholding is not an additional tax, and any amounts withheld under the backup withholding rules may be credited against your U.S. federal income tax liability (which may result in your being entitled to a refund of U.S. federal income tax), provided the required information is timely provided to the IRS.

Non-U.S. Holders

The following summary applies to you if you are a beneficial owner of a note or notes and you are neither a U.S. Holder (as defined above) nor an entity or arrangement classified as a partnership for U.S. federal tax purposes (a “non-U.S. Holder”).

U.S. Federal Withholding Tax

Subject to the discussions below regarding backup withholding and FATCA (as defined below), U.S. federal withholding tax will generally not apply to payments of stated interest on your notes under the “portfolio interest” exception of the Internal Revenue Code, provided that:

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The applicable Treasury regulations provide alternative methods for satisfying the foregoing certification requirement. In addition, under these Treasury regulations, special rules apply to pass-through entities and this certification requirement may also apply to beneficial owners of pass-through entities.

If you cannot satisfy the requirements of the “portfolio interest” exception described above, payments of stated interest made to you will be subject to 30% U.S. federal withholding tax unless you provide the applicable withholding agent with a properly executed (1) IRS Form W-8ECI (or other applicable form) stating that interest paid on your notes is not subject to withholding tax because it is effectively connected with your conduct of a trade or business within the United States, or (2) IRS Form W-8BEN or W-8BEN-E (or other applicable form) claiming an exemption from or reduction in this withholding tax under an applicable income tax treaty.

Any gain recognized upon a sale, exchange, retirement, redemption or other taxable disposition of a note (other than any amount representing accrued but unpaid stated interest paid by us, which is treated as described immediately above) generally will not be subject to U.S. federal withholding tax, subject to the discussions below regarding backup withholding and FATCA.

U.S. Federal Income Tax

Except for the possible application of U.S. federal withholding tax (see above) and backup withholding and FATCA (see below), you generally will not have to pay U.S. federal income tax on payments of principal of and stated interest on your notes, or on any gain realized from (or accrued stated interest treated as received in connection with) the sale, exchange, redemption, retirement or other taxable disposition of your notes unless:

If you are engaged in a trade or business within the United States, and stated interest or gain in respect of your notes is effectively connected with the conduct of your trade or business, the stated interest or gain generally will be exempt from U.S. federal withholding tax as described above and instead will be subject to U.S. federal income tax on a net basis at the regular graduated rates and in the manner applicable to a U.S. Holder (unless an applicable income tax treaty provides otherwise). In addition, if you are a non-U.S. Holder that is a corporation, you may be subject to a branch profits tax equal to 30% of your effectively connected earnings and profits for the taxable year, as adjusted for certain items, unless a lower rate applies to you under an applicable income tax treaty.

Backup Withholding and Information Reporting

Generally, the applicable withholding agent will be required to report to the IRS and to you payments of stated interest on the notes and the amount of U.S. federal income tax, if any, withheld with respect to those payments. Copies of the information returns reporting such stated interest payments and any withholding may also be made available to the tax authorities in the country in which you reside under the provisions of a treaty or agreement.

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Backup withholding will not apply to payments of stated interest made on the notes to you if you have provided to the applicable withholding agent the required certification that you are not a “United States person” within the meaning of the Internal Revenue Code as described in “—U.S. Federal Withholding Tax” above, provided that the applicable withholding agent does not have actual knowledge or reason to know that you are a United States person.

The gross proceeds from the sale, exchange, retirement, redemption or other disposition of your notes may be subject, in certain circumstances discussed below, to information reporting and backup withholding (currently at a rate of 24%). If you sell your notes outside the United States through a non-U.S. office of a non-U.S. broker and the sales proceeds are paid to you outside the United States, then the backup withholding and information reporting requirements generally will not apply to that payment. However, information reporting, but not backup withholding, will apply to a payment of sales proceeds, even if that payment is made outside the United States, if you sell your notes through a non- U.S. office of a broker that is a United States person (as defined in the Internal Revenue Code) or has certain enumerated connections with the United States, unless the broker has documentary evidence in its files that you are not a United States person and certain other conditions are met or you otherwise establish an exemption. If you receive payment of the proceeds from a sale of your notes through a U.S. office of a broker, the payment will be subject to both backup withholding and information reporting unless you provide an IRS Form W-8BEN or W-8BEN-E (or other applicable form) certifying that you are not a United States person or you otherwise establish an exemption, provided that the broker does not have actual knowledge, or reason to know, that you are a United States person or that the conditions of any other exemption are not, in fact, satisfied. You should consult your own tax advisor regarding application of the backup withholding rules in your particular circumstances and the availability of and procedure for obtaining an exemption from backup withholding.

Backup withholding is not an additional tax, and any amounts withheld under the backup withholding rules may be credited against your U.S. federal income tax liability (which may result in your being entitled to a refund of U.S. federal income tax), provided the required information is timely provided to the IRS.

U.S. Federal Estate Tax

Unless otherwise provided in an applicable estate tax or other treaty, if you are an individual and are not a U.S. citizen or a resident of the United States (as specially defined for U.S. federal estate tax purposes) at the time of your death, your notes generally will not be subject to the U.S. federal estate tax, unless, at the time of your death:

Foreign Account Tax Compliance Act

The Foreign Account Tax Compliance Act and related Treasury guidance (commonly referred to as “FATCA”) impose U.S. federal withholding tax at a rate of 30% on payments of (i) U.S.-source interest (including interest paid on the notes) and (ii) the gross proceeds from the sale or other disposition of an obligation that produces U.S.-source interest (including the sale, exchange, redemption, retirement or other taxable disposition of the notes). Under recently proposed Treasury regulations that may be relied upon pending finalization, the withholding tax on gross proceeds would be eliminated and, consequently, FATCA withholding on gross proceeds is not currently expected to apply. The withholding tax applies to a foreign entity, whether acting as a beneficial owner or as an intermediary, unless such foreign entity complies with (i) certain information reporting requirements regarding its U.S. account holders and its U.S. owners and (ii) certain

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withholding obligations regarding certain payments to its account holders and certain other persons. Accordingly, the entity through which a U.S. Holder or a non-U.S. Holder holds its notes will affect the determination of whether such withholding is required. An intergovernmental agreement between the United States and an applicable foreign country, or future Treasury regulations or other guidance, may modify these requirements. We will not pay any additional amounts to U.S. Holders or non-U.S. Holders in respect of any amounts withheld under FATCA. U.S. Holders that own their interests in a note through a foreign entity or intermediary, and non-U.S. Holders, are encouraged to consult their tax advisors regarding FATCA.

THE PRECEDING SUMMARY OF CERTAIN U.S. FEDERAL TAX CONSEQUENCES IS FOR GENERAL INFORMATION ONLY AND IS NOT TAX ADVICE. YOU SHOULD CONSULT YOUR OWN TAX ADVISOR REGARDING THE PARTICULAR U.S. FEDERAL, STATE, LOCAL AND NON U.S. TAX CONSEQUENCES OF PURCHASING, OWNING AND DISPOSING OF NOTES, INCLUDING THE CONSEQUENCES OF ANY PROPOSED CHANGES IN APPLICABLE LAWS.

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UNDERWRITING

Subject to the terms and conditions contained in an underwriting agreement, dated as of the date of this prospectus supplement, between us and the underwriters named below, for whom Goldman Sachs & Co. LLC, J.P. Morgan Securities LLC and Morgan Stanley & Co. LLC are acting as representatives, we have agreed to sell to each underwriter, and each underwriter has severally agreed to purchase from us, the principal amount of notes that appears opposite its name in the table below:

The underwriters are offering the notes subject to their acceptance of the notes from us and subject to prior sale. The underwriting agreement provides that the obligations of the several underwriters to pay for and accept delivery of the notes offered by this prospectus supplement are subject to certain conditions. The underwriters are obligated to take and pay for all of the notes offered by this prospectus supplement if any such notes are taken.

The underwriters initially propose to offer some of the notes to the public at the public offering prices that appear on the cover page of this prospectus supplement. In addition, the underwriters initially propose to offer some of the notes to certain dealers at the public offering prices less a concession not to exceed 0.210% of the principal amount, with respect to the 2024 notes, 0.300% of the principal amount, with respect to the 2029 notes, 0.450% of the principal amount, with respect to the 2039 notes and 0.450% of the principal amount, with respect to the 2049 notes. Any underwriter may allow, and any such dealer may reallow, a concession not to exceed 0.100% of the principal amount, with respect to the 2024 notes, 0.200% of the principal amount, with respect to the 2029 notes, 0.250% of the principal amount, with respect to the 2039 notes and 0.250% of the principal amount, with respect to the 2049 notes, on sales to certain other dealers. After the initial offering of the notes to the public, the representatives may change the public offering prices and concessions. The underwriters may from time to time vary the offering prices and other selling terms. The underwriters may offer and sell notes through certain of their affiliates. The offering of the notes by the underwriters is subject to receipt and acceptance and subject to the underwriters’ right to reject any order in whole or in part.

The following table shows the underwriting discounts that we will pay to the underwriters in connection with the offering of the notes:

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Expenses associated with this offering to be paid by us, other than underwriting discounts, are estimated to be approximately $5 million. The underwriters have agreed to reimburse us for certain of our expenses in connection with this offering.

We have also agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments which the underwriters may be required to make in respect of any such liabilities.

The notes are new issues of securities, and there are currently no established trading markets for the notes. We do not intend to apply for the notes to be listed on any securities exchange or automated dealer quotation system. The underwriters have advised us that they intend to make a market in the notes of each series, but they are not obligated to do so. The underwriters may discontinue any market making in the notes at any time at their sole discretion. Accordingly, we cannot assure you that liquid trading markets will develop for the notes, that you will be able to sell your notes at a particular time or that the prices you receive when you sell will be favorable.

In connection with the offering of the notes, the underwriters may engage in transactions that stabilize, maintain or otherwise affect the prices of the notes. Specifically, the underwriters may overallot in connection with the offering of the notes, creating syndicate short positions. In addition, the underwriters may bid for and purchase notes in the open market to cover syndicate short positions or to stabilize the prices of the notes. Finally, the underwriting syndicate may reclaim selling concessions allowed for distributing the notes in the offering of the notes, if the syndicate repurchases previously distributed notes in syndicate covering transactions, stabilization transactions or otherwise. Any of these activities may stabilize or maintain the market prices of the notes above independent market levels. The underwriters are not required to engage in any of these activities, and may end any of them at any time.

Other Relationships

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. From time to time in the ordinary course of their respective businesses, certain of the underwriters and their affiliates have engaged in and may in the future engage in commercial banking, derivatives and/or financial advisory, investment banking and other commercial transactions and services with us and our affiliates for which they have received or will receive customary fees and commissions. In addition, U.S. Bancorp Investments, Inc., one of the underwriters, is an affiliate of the trustee.

Substantially all of the underwriters or their affiliates are participants in our $6.0 billion, five-year credit facility maturing in June 2023. Certain of the underwriters or their affiliates are or may serve as dealers in our commercial paper program.

In addition, in the ordinary course of their business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. If any of the underwriters or their affiliates have a lending relationship with us, certain of those underwriters or their affiliates routinely hedge, and certain other of those underwriters or their affiliates may hedge, their credit exposure to us consistent with their customary risk management policies. Typically, these underwriters and their affiliates would hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities, including potentially the notes offered hereby. Any such credit default swaps or short positions could adversely affect future trading prices of the notes offered hereby. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

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Selling Restrictions

The notes may not be offered or sold, directly or indirectly, nor may this prospectus supplement or any other offering material or advertisements in connection with the offer and sale of any such notes be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus supplement comes are advised to inform themselves about and to observe any restrictions relating to the offering of the notes and the distribution of this prospectus supplement. This prospectus supplement does not constitute an offer to sell or a solicitation of an offer to buy any notes offered by this prospectus supplement in any jurisdiction in which such an offer or a solicitation is unlawful.

Notice to Prospective Investors in the European Economic Area

The notes described herein are not intended to be offered, sold or otherwise made available to and should not be offered, sold or otherwise made available to any retail investor in the European Economic Area (“EEA”). For these purposes, a retail investor means a person who is one (or more) of: (i) a retail client as defined in point (11) of Article 4(1) of Directive 2014/65/EU (as amended, “MiFID II”); or (ii) a customer within the meaning of Directive 2016/97/EU (as amended, the “Insurance Distribution Directive”), where that customer would not qualify as a professional client as defined in point (10) of Article 4(1) of MiFID II; or (iii) not a qualified investor as defined in Directive 2003/71/EC (as amended, the “Prospectus Directive”). Consequently no key information document required by Regulation (EU) No 1286/2014 (as amended, the “PRIIPs Regulation”) for offering or selling the notes or otherwise making them available to retail investors in the EEA has been prepared and therefore offering or selling the notes or otherwise making them available to any retail investor in the EEA may be unlawful under the PRIIPs Regulation. This prospectus supplement has been prepared on the basis that any offer of notes in any Member State of the EEA will be made pursuant to an exemption under the Prospectus Directive from the requirement to publish a prospectus for offers of notes. This prospectus supplement is not a prospectus for the purposes of the Prospectus Directive.

Notice to Prospective Investors in the United Kingdom

Each underwriter has represented and agreed that: (a) it has only communicated or caused to be communicated and will only communicate or cause to be communicated an invitation or inducement to engage in investment activity (within the meaning of Section 21 of the Financial Services and Markets Act 2000 (“FSMA”)) received by it in connection with the issue or sale of the notes in circumstances in which Section 21(1) of the FSMA does not apply to the issuer; and (b) it has complied and will comply with all applicable provisions of the FSMA with respect to anything done by it in relation to the notes in, from or otherwise involving the United Kingdom.

Notice to Prospective Investors in Canada

The notes may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the notes must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 (or, in the case of securities issued or guaranteed by the government of a non-Canadian jurisdiction, section 3A.4) of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the

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underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

Notice to Prospective Investors in Hong Kong

The notes may not be offered or sold in Hong Kong by means of any document other than (a) to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong and any rules made thereunder; or (b) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong or which do not constitute an offer to the public within the meaning of that Ordinance. No advertisement, invitation or document relating to the notes has been or may be issued or has been or may be in the possession of any person for the purposes of issue, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to notes which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the Securities and Futures Ordinance and any rules made under that Ordinance.

Notice to Prospective Investors in Japan

The notes have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended) and, accordingly, will not be offered or sold, directly or indirectly, in Japan, or for the benefit of any Japanese Person or to others for re-offering or resale, directly or indirectly, in Japan or to any Japanese Person, except in compliance with all applicable laws, regulations and ministerial guidelines promulgated by relevant Japanese governmental or regulatory authorities in effect at the relevant time. For the purposes of this paragraph, “Japanese Person” shall mean any person resident in Japan, including any corporation or other entity organized under the laws of Japan.

Notice to Prospective Investors in Singapore

This prospectus supplement and the accompanying prospectus have not been and will not be registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and the accompanying prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the notes may not be circulated or distributed, nor may the notes be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275 of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the notes are subscribed or purchased under Section 275 by a relevant person which is: (a) a corporation (which is not an accredited investor) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or (b) a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary is an accredited investor, shares, debentures and units of shares and debentures of that corporation or the beneficiaries’ rights and interest in that trust shall not be transferred within six months after that corporation or that trust has acquired the notes under Section 275 except: (1) to an institutional investor under Section 274 of the SFA or to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275 of the SFA; (2) where no consideration is or will be given for the transfer; or (3) the transfer is by operation of law.

Singapore SFA Product Classification—In connection with Section 309B of the SFA and the CMP Regulations 2018, the Issuer has determined, and hereby notifies all relevant persons (as defined in the CMP Regulations 2018), that the notes are “prescribed capital markets products” (as defined in the CMP Regulations 2018) and Excluded Investment Products (as defined in MAS Notice SFA 04-N12: Notice on the Sale of Investment Products and MAS Notice FAA-N16: Notice on Recommendations on Investment Products).

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INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” the information in documents that we file with them. This means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus supplement and the accompanying prospectus. The information we incorporate by reference into this prospectus supplement supersedes the information incorporated by reference in the accompanying prospectus, and information in documents that we file after the date of this prospectus supplement and before the termination of the offering to which this prospectus supplement relates will automatically update information in this prospectus supplement and the accompanying prospectus. We incorporate by reference the documents listed below and filed with the SEC as well as any future filings under Exchange Act File No. 001-06571 we will make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the termination of the offering to which this prospectus supplement relates (other than Current Reports or portions thereof furnished under Item 2.02 or Item 7.01 of Form 8-K):

We will provide, without charge, copies of any document incorporated by reference into this prospectus supplement, excluding exhibits other than those that are specifically incorporated by reference into this prospectus supplement. You can obtain a copy of any document incorporated by reference by writing or calling us at our principal executive offices as follows:

Merck & Co., Inc.

2000 Galloping Hill Road

Kenilworth, New Jersey 07033 USA

908-740-4000

Attention: Stockholder Services Department

VALIDITY OF THE NOTES

The validity of the notes will be passed upon for us by Jennifer Zachary, our Executive Vice President and General Counsel, and for the underwriters by Davis Polk & Wardwell LLP, New York, New York. In addition, Fried, Frank, Harris, Shriver & Jacobson LLP, New York, New York, has represented us in connection with various matters for this offering. As of March 5, 2019, Ms. Zachary owned, directly and indirectly, 17,316 of our restricted stock units, each representing a contingent right to receive one share of our common stock, and options to purchase 73,191 shares of our common stock.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this prospectus supplement by reference to the Annual Report on Form 10-K for the year ended December 31, 2018 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

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PROSPECTUS

Merck & Co., Inc.

Debt Securities

Merck & Co., Inc. may from time to time issue debt securities in one or more offerings pursuant to this prospectus. The accompanying prospectus supplement will specify the terms of the debt securities, including whether they are guaranteed. We urge you to read carefully this prospectus, any accompanying prospectus supplement, and any documents we incorporate by reference in this prospectus and any accompanying prospectus supplement before you make your investment decision.

Merck & Co., Inc. may sell these debt securities to or through underwriters, dealers and agents, or directly to purchasers, on a delayed or continuous basis.

This prospectus describes some of the general terms that may apply to the debt securities and the general manner in which they may be offered. The specific terms of the debt securities, including whether such debt securities will be guaranteed, and the specific manner in which they may be offered, including the names of any underwriters or agents, will be described in a supplement to this prospectus.

Investing in our debt securities involves risks. You should carefully consider all of the information set forth in this prospectus, including under “Risk Factors” on page 2 of this prospectus, and in any prospectus supplement or documents we incorporate by reference in this prospectus or any prospectus supplement before deciding to invest in any of our debt securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is March 29, 2018.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the Commission, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended, or the Securities Act, utilizing a “shelf” registration process. Under this shelf process, we may, from time to time, sell any combination of the debt securities described in this prospectus in one or more offerings. No limit exists on the aggregate amount of debt securities we may sell pursuant to the registration statement.

This prospectus provides you with a general description of the debt securities we may offer. Certain portions of the registration statement and the exhibits thereto have been omitted pursuant to the rules and regulations of the Commission. Reference is hereby made to such omitted portions for further information with respect to us and the debt securities offered hereby. A copy of the registration statement may be inspected or obtained from us at the telephone number and address set forth in “Incorporation of Certain Documents by Reference” below. Each time we sell debt securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering, including the specific amounts, prices and terms of the debt securities offered, and whether they will be guaranteed by any of our subsidiaries. Any prospectus supplement may also add, update or change information contained in this prospectus. You should read this prospectus, any prospectus supplement to this prospectus, any documents that we incorporate by reference in this prospectus and any prospectus supplement and the additional information described below under “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference” before making an investment decision. You should rely only on the information contained or incorporated by reference in this prospectus and any prospectus supplement, which may add, update or change information contained in this prospectus. We have not authorized any other person to provide you with additional or different information. If anyone provides you with additional, different or inconsistent information, you should not rely on it. We are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted.

Neither the delivery of this prospectus nor any sales hereunder shall under any circumstances create any implication that there has been no change in the affairs of Merck since the date hereof. You should not assume that the information in this prospectus, any accompanying prospectus supplement or any documents we incorporate by reference in this prospectus and any prospectus supplement is accurate as of any date other than the date on the front of those documents or on other dates which are specified in those documents. Our business, financial condition, results of operations and prospects may have changed since that date.

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MERCK

We are a global health care company that delivers innovative health solutions through our prescription medicines, vaccines, biologic therapies and animal health products. Our operations are principally managed on a products basis and include four operating segments, which are the Pharmaceutical, Animal Health, Healthcare Services and Alliances segments. The Pharmaceutical segment is the only reportable segment.

The Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. We sell these human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies and managed health care providers such as health maintenance organizations, pharmacy benefit managers and other institutions. Vaccine products consist of preventive pediatric, adolescent and adult vaccines, primarily administered at physician offices. We sell these human health vaccines primarily to physicians, wholesalers, physician distributors and government entities.

We also have an Animal Health segment that discovers, develops, manufactures and markets animal health products, including vaccines, which we sell to veterinarians, distributors and animal producers. Our Healthcare Services segment provides services and solutions that focus on engagement, health analytics and clinical services to improve the value of care delivered to patients.

We were incorporated in the State of New Jersey and maintain our principal offices in Kenilworth, New Jersey. Our address is 2000 Galloping Hill Road, Kenilworth, New Jersey 07033, and our telephone number is (908) 740-4000. Our website is located at www.merck.com. Information available on, or accessible through, our website is not incorporated into this prospectus by reference and should not be considered a part of this prospectus.

RISK FACTORS

Before deciding to invest in Merck’s debt securities, you should carefully consider the risk factors and forward-looking statements described in Item 1A of our most recent Annual Report on Form 10-K for the year ended December 31, 2017 (which is incorporated by reference herein). In addition, you should carefully consider information in any accompanying prospectus supplement or any documents we incorporate by reference in this prospectus and any accompanying prospectus supplement, before deciding to invest in Merck’s debt securities. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also impair our business operations.

FORWARD-LOOKING STATEMENTS

This prospectus, any prospectus supplement and any documents we incorporate by reference herein or therein and oral statements made from time to time by us may contain so called “forward-looking statements” (within the meaning of Section 27A of the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act), all of which are based on management’s current expectations and are subject to risks and uncertainties which may cause results to differ materially from those set forth in the statements. One can identify these forward-looking statements by their use of words such as “anticipates,” “expects,” “plans,” “will,” “estimates,” “forecasts,” “projects” and other words of similar meaning, or negative variations of any of the foregoing. One can also identify them by the fact that they do not relate strictly to historical or current facts. These statements are likely to address our growth strategy, financial results, product development, product approvals, product potential and development programs. One must carefully consider any such statement and should understand that many factors could cause actual results to differ materially from our forward-looking statements. These factors include inaccurate assumptions and a broad variety of other risks and uncertainties,

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including some that are known and some that are not known. No forward-looking statement can be guaranteed and actual future results may vary materially. We do not assume the obligation to update any forward-looking statement. We caution you not to place undue reliance on these forward-looking lstatements. One should carefully evaluate such statements in light of factors, including risk factors, described under “Risk Factors” above and in the documents incorporated herein by reference in which we discuss in more detail various important factors that could cause actual results to differ from expected or historic results. One should understand that it is not possible to predict or identify all such factors. Consequently, one should not consider any such list to be a complete statement of all potential risks or uncertainties.

RATIOS OF EARNINGS TO FIXED CHARGES

Our consolidated ratios of earnings to fixed charges for each of the fiscal years ended December 31, 2013 through 2017 are as follows:

For purposes of computing these ratios, “earnings” consist of income before taxes, one-third of rents (deemed by us to be representative of the interest factor inherent in rents), interest expense, interest capitalized, net of amortization and equity (income) loss from affiliates, net of distributions. “Fixed charges” consist of one-third of rents, interest expense and dividends on preferred stock. Interest expense does not include interest related to uncertain tax positions.

USE OF PROCEEDS

Unless otherwise indicated in the accompanying prospectus supplement, we will use the net proceeds from the sale of the debt securities for general corporate purposes, including the reduction of short-term debt. We may temporarily invest funds that we do not immediately need for these purposes in short-term marketable securities.

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DESCRIPTION OF DEBT SECURITIES WE MAY OFFER

General

In this description “we,” “our” and “us” refer to Merck & Co., Inc., but not to any of Merck & Co., Inc.’s subsidiaries. “You” means direct holders and not street name or other indirect holders of debt securities. Indirect holders should read the information under the caption “Legal Ownership and Book-Entry Issuance.”

The debt securities are not secured by any of our property or assets. Accordingly, your ownership of debt securities means you are one of our unsecured creditors. The debt securities are not subordinated to any of our other debt obligations and therefore they rank equally with all our other unsecured and unsubordinated indebtedness.

As required by federal law for all bonds and notes that are publicly offered, a document called the indenture governs the debt securities. The indenture is a contract, dated as of January 6, 2010, which we may amend in the future, between us and U.S. Bank Trust National Association, which acts as trustee. The trustee has two main roles. First, the trustee can enforce your rights against us if we default. There are some limitations on the extent to which the trustee acts on your behalf, described under “—Defaults and Remedies—Events of Default—Remedies if an Event of Default Occurs.” Second, the trustee performs administrative duties for us, such as sending you interest payments, registering transfers of your debt securities to a new buyer if you sell and sending you notices.

The indenture and its associated documents contain the full legal text of the matters described in this section. New York law governs the indenture and will govern the debt securities. The indenture is an exhibit to our registration statement of which this prospectus forms a part. See “Where You Can Find More Information” for information on how to obtain a copy.

We may issue as many distinct series of debt securities under the indenture as we wish. A series of debt securities may be guaranteed by one or more of our subsidiaries. There is no limit on the amount of debt securities we may issue under the indenture and the provisions of the indenture allow us to issue debt securities with terms different from those previously issued under the indenture. Also, we may “reopen” a previous issue of a series of debt securities and issue additional debt securities of that series. We may issue debt securities in amounts that exceed the total amount specified on the cover of your prospectus supplement at any time without your consent and without notifying you.

This section summarizes all the material terms of the debt securities that are common to all series unless otherwise indicated in the prospectus supplement relating to a particular series. Because this section is a summary, it does not describe every aspect of the debt securities and is subject to and qualified in its entirety by reference to all the provisions of the indenture, including definitions of some of the terms used in the indenture. We describe the meaning for only some of the important terms. We also include references in parentheses to some sections of the indenture. Whenever we refer to particular sections or defined terms of the indenture in this prospectus or in the prospectus supplement, we incorporate by reference those sections or defined terms here or in the prospectus supplement.

We may issue the debt securities as original issue discount securities, which we would offer and sell at a substantial discount below their stated principal amount. (section 101) A prospectus supplement relating to original issue discount securities will describe federal income tax consequences and other special considerations applicable to them. We may also issue the debt securities as indexed securities or securities denominated in foreign currencies, currency units or composite currencies, as described in more detail in a prospectus supplement relating to any of these types of debt securities. A prospectus supplement relating to indexed debt securities or foreign currency debt securities will also describe any additional tax consequences or other special considerations applicable to these types of debt securities.

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In addition, we will describe the material specific financial, legal and other terms particular to debt securities of each series in a prospectus supplement relating to debt securities of that series. A prospectus supplement relating to debt securities of a series will describe the following terms of the debt securities:

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We will attach the prospectus supplement relating to the debt securities of the series to the front of this prospectus.

We may issue debt securities other than the debt securities described in this prospectus. There is no requirement that we issue any other debt securities under the indenture described herein. Thus, we may issue any other debt securities under other indentures or documentation, containing provisions different from those included in the indenture or applicable to one or more issues of the debt securities described in this prospectus.

Without limiting the foregoing, we and the trustee may enter into one or more supplemental indentures with one or more of our subsidiaries providing for a full and unconditional guarantee by such subsidiaries of the payment of principal of, premium, if any, and interest on and “additional amounts” with respect to these debt securities when due, whether at maturity or otherwise. The debt securities described herein will be effectively subordinated to any secured debt we or our subsidiaries incur to the extent of the value of such security. The debt securities will also be structurally subordinated to all indebtedness of our subsidiaries which are not guarantors of the debt securities.

Overview of Remainder of this Description

The remainder of this description summarizes:

Additional Mechanics

Form, Exchange and Registration of Transfer

We will issue the debt securities:

You may have your debt securities broken into more debt securities of smaller denominations of not less than $2,000 or combined into fewer debt securities of larger denominations, as long as the total principal amount is not changed. (section 305) This is called an exchange.

You may exchange or register a transfer of debt securities at the office of the trustee. The trustee acts as our agent for registering debt securities in the names of holders and registering transfers of debt securities. We may change

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this appointment to another entity or perform it ourselves. The entity performing the role of maintaining the list of registered direct holders is called the security registrar. It will also register transfers. (section 305) You may also replace lost, stolen or mutilated debt securities at that office. (section 306) The trustee’s agent may require an indemnity before replacing any debt securities.

You will not be required to pay a service charge to register a transfer of debt securities or to exchange debt securities, but you may be required to pay for any tax or other governmental charge associated with the transfer or exchange. The security registrar will make the registration of transfer or exchange only if it is satisfied with your proof of ownership. (section 305)

If we have designated additional trustees, they are named in the prospectus supplement. We may cancel the designation of any particular trustee. We may also approve a change in the office through which any trustee acts. (section 1002)

If the debt securities are redeemable and we redeem less than all of the debt securities of a particular series, we may block the issuance of, registration of transfer or exchange of debt securities during the period beginning 15 days before the day we mail the notice of redemption and ending on the day of that mailing, in order to freeze the list of holders to prepare the mailing. We may also refuse to register transfers or exchanges of debt securities selected for redemption, except that we will continue to permit transfers and exchanges of the unredeemed portion of any debt security being partially redeemed. (section 305)

The rules for exchange described above apply to exchange of debt securities for other debt securities of the same series and tenor.

Payment and Paying Agents

We will pay interest to you on each date interest is due if you are a direct holder listed in the trustee’s records at the close of business on a particular day in advance of each due date for interest, even if you no longer own the debt security on the interest due date. That particular day is called the regular record date and is stated in the prospectus supplement. (section 307) Holders buying and selling debt securities must work out between them how to compensate for the fact that we will pay all the interest for an interest period to the one who is the registered holder on the regular record date.

Unless otherwise stated in the prospectus supplement, we will pay interest, principal and any other money due on the debt securities at the corporate trust office of the trustee in New York City. (section 1002) That office is currently located at 100 Wall Street, 16th floor, New York, New York 10005. You must make arrangements to have your payments picked up at or wired from that office. We may also choose to pay interest by mailing checks.

Street name and other indirect holders should consult their banks or brokers for information on how they will receive payments.

We may also arrange for additional payment offices, and may cancel or change these offices, including our use of the trustee’s corporate trust office. These offices are called paying agents. We may also choose to act as our own paying agent. We must notify you of changes in the paying agents for any particular debt securities of the series. (section 1002)

Notices

We and the trustee will send notices regarding the debt securities only to direct holders, using their addresses as listed in the trustee’s records. (section 106)

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All paying agents must return to us upon our request all money paid by us that remains unclaimed two years after the amount is due to direct holders. After that two-year period, you may look only to us for payment and not to the trustee, any other paying agent or anyone else. (section 1003)

Special Situations

Mergers and Similar Events

We may consolidate or merge with another company or firm. We may also convey, transfer or lease all of our properties and assets substantially as an entirety to another firm, or buy or lease substantially all of the assets of another firm. However, we may not take any of these actions unless the following conditions, among others, are met:

If the conditions described above are satisfied with respect to any series of debt securities, we will not need to obtain the approval of the holders of those debt securities in order to merge or consolidate or to sell our assets. Also, these conditions will apply only if we wish to merge or consolidate with another entity or convey, transfer or lease all of our properties and assets substantially as an entirety. We will not need to satisfy these conditions if we enter into other types of transactions, including any transaction in which we acquire the stock or assets of another entity, any transaction that involves a change of control but in which we do not merge or consolidate and any transaction in which we convey, transfer or lease less than all of our properties and assets substantially as an entirety. It is possible that these other types of transactions may result in a reduction in our credit rating, may reduce our operating results or may impair our financial condition. However, you will have no approval right with respect to any transaction of this type.

Modification and Waiver

There are three types of changes we can make to the indenture and the debt securities.

Changes Requiring Your Approval. First, there are changes that cannot be made to your debt securities without your specific approval. Following is a list of those types of changes:

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Changes Requiring a Majority Vote. The second type of change to the indenture and the debt securities is the kind that requires a vote in favor by direct holders owning not less than a majority of the principal amount of the debt securities of the particular series affected. (section 902) Most changes fall into this category, such as if we wish to obtain a waiver of all or part of the restrictive covenants described below, or a waiver of a past default. However, we cannot obtain a waiver of a payment default or any other aspect of the indenture or the debt securities listed in the first category above under “—Changes Requiring Your Approval” unless we obtain your individual consent to the waiver. (section 513)

Changes Not Requiring Approval. The third type of change does not require any vote by holders of debt securities. This type is limited to the addition or release of a guarantee, corrections and clarifications and other changes that would not adversely affect holders of the debt securities. (section 901)

Further Details Concerning Voting. When taking a vote, we will use the following rules to decide how much principal amount to attribute to a debt security:

Debt securities will not be considered outstanding and therefore will not carry voting rights if we have deposited or set aside in trust for you money for their payment or redemption. Debt securities will also not be eligible to vote if they have been fully defeased as described under “—Defeasance—Full Defeasance.” (section 1302)

We may set any day as a record date for the purpose of determining the direct holders of outstanding debt securities that are entitled to vote or take other action under the indenture. (section 104) In some circumstances, the trustee may set a record date for action by direct holders.

Street name and other indirect holders should consult their banks or brokers for information on how approval may be granted or denied if we seek to change the indenture or the debt securities or request a waiver.

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Restrictive Covenants

In the following description of restrictive covenants, we use several specialized terms without explaining the meaning when we use the terms. We define these terms, which appear in bold, italicized type without quotation marks the first time they appear, in “—Definitions Relating to our Restrictive Covenants” at the end of this subsection.

Restrictions on Secured Debt. Some of our property may be subject to a mortgage or other legal mechanism that gives our lenders preferential rights in that property over other lenders, including you and the other direct holders of the debt securities, or over our general creditors if we fail to pay them back. These preferential rights are called liens. Debt which is protected by these preferential rights is called secured debt. In the indenture, we promise that neither we nor our domestic subsidiaries will incur any new secured debt that is secured by a lien on any of our or our domestic subsidiaries’ principal domestic manufacturing properties, or on any shares of stock of any of our domestic subsidiaries that own or lease a principal domestic manufacturing property, unless we grant an equivalent or higher-ranking lien on the same property to you and the other direct holders of the debt securities.

We do not need to comply with this restriction if the amount of all debt that would be secured by liens on principal domestic manufacturing properties, including the new debt, the debt securities which we would so secure as described in the previous sentence, and all attributable debt that results from a sale and leaseback transaction involving principal domestic manufacturing properties, is less than 10% of our consolidated net tangible assets.

This restriction on secured debt does not apply to debt secured by certain types of liens, and we can disregard this secured debt when we calculate the limits imposed by this restriction. These types of liens are:

We and our subsidiaries may have as much unsecured debt as we may choose. (section 1006)

Restrictions on Sales and Leasebacks. We promise that neither we nor any of our domestic subsidiaries will enter into any sale and leaseback transaction involving a principal domestic manufacturing property, unless we comply with this restrictive covenant. A sale and leaseback transaction generally is an arrangement between us or a

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domestic subsidiary and a bank, insurance company or other lender or investor where we or the domestic subsidiary sell a property to a lender or investor more than 120 days after the acquisition of the property or the completion of construction of the property and the beginning of its full operation and we lease the property back from the lender.

We can comply with this restrictive covenant in either of two ways:

This restriction on sales and leasebacks does not apply to any sale and leaseback transaction that is between us and one of our domestic subsidiaries or between domestic subsidiaries, or that involves a lease for a period of three years or less. (section 1007)

Definitions Relating to our Restrictive Covenants. Following are summaries of the meanings of the terms that are important in understanding the restrictive covenants previously described:

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Defeasance

The following discussion of full defeasance and covenant defeasance will be applicable to your debt securities only if we choose to have those provisions apply to securities of that series. If we do so choose, we will state that in the prospectus supplement. (section 1301)

Full Defeasance. If there is a change in federal tax law, as described below, we can legally release ourselves from any payment or other obligations on the debt securities of a series if we put in place other arrangements for you to be repaid. This is called full defeasance. In order to achieve full defeasance, we must do the following, among other things:

If we ever did accomplish full defeasance, as described above, you would have to rely solely on the trust deposit for repayment on the debt securities. You could not look to us for repayment in the unlikely event of any shortfall. (sections 1302 and 1304)

Covenant Defeasance. Under current federal tax law, we can make the same type of deposit described above and be released from some of the restrictive covenants in the debt securities. This is called covenant defeasance. In that event, you would lose the protection of those restrictive covenants but would gain the protection of having money and securities set aside in trust to repay the debt securities. In order to achieve covenant defeasance of the debt securities of a series, we must do the following:

If we accomplish covenant defeasance, the following provisions of the indenture and the debt securities would no longer apply:

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If we accomplish covenant defeasance, you can still look to us for repayment of the debt securities if there were a shortfall in the trust deposit. In fact, if one of the remaining events of default occurred, such as our bankruptcy, and the debt securities become immediately due and payable, there may be such a shortfall in the trust deposit. (sections 1303 and 1304)

Default and Remedies—Events of Default

You will have special rights if an event of default occurs and is not cured, as described later in this subsection.

What Is an Event of Default?

The term event of default with respect to your series of debt securities means any of the following:

Remedies if an Event of Default Occurs.

If an event of default has occurred and has not been cured, the trustee or the direct holders of at least 25% in principal amount of the outstanding debt securities of the affected series may declare the entire principal amount of all the debt securities of that series to be due and immediately payable. This is called a declaration of acceleration. The direct holders of at least a majority in principal amount of the debt securities of the affected series may cancel a declaration of acceleration of maturity. (section 502)

Except in cases of default, where the trustee has some special duties, the trustee is not required to take any action under the indenture at the request of any holders unless the direct holders offer the trustee reasonable protection, called an indemnity, against expenses and liability. (section 603) If reasonable indemnity is provided, the direct holders of a majority in principal amount of the outstanding debt securities of the relevant series may direct the time, method and place of conducting any lawsuit or other formal legal action seeking any remedy available to the trustee. These majority direct holders may also direct the trustee in performing any other action under the indenture. (section 512)

Before you bypass the trustee and bring your own lawsuit or other formal legal action or take other steps to enforce your rights or protect your interests relating to the debt securities, the following must occur:

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However, you are entitled at any time to bring a lawsuit for the payment of money due on your debt security on or after its due date. (section 508)

Street name and other indirect holders should consult their banks or brokers for information on how to give notice or direction to or make a request of the trustee and to make or cancel a declaration of acceleration.

We will furnish to the trustee every year a written statement of our principal executive, financial or accounting officer certifying that to the best of such signer’s knowledge we are in compliance with the indenture and the debt securities, or else specifying any default. (section 1004)

Our Relationship with the Trustee

U.S. Bank Trust National Association is the trustee under the indenture. The trustee performs services for us in the ordinary course of business.

LEGAL OWNERSHIP AND BOOK-ENTRY ISSUANCE

Street Name and Other Indirect Holders

We generally will not recognize investors who hold debt securities in accounts at banks or brokers as legal holders of debt securities. Holding in that way is called holding in street name. Instead, we would recognize only the bank or broker, or the financial institution the bank or broker uses to hold its debt securities. These intermediary banks, brokers and other financial institutions pass along principal, interest and other payments on the debt securities, either because they agree to do so in their customer agreements or because they are legally required to. If you hold debt securities in street name, you should check with your own institution to find out:

Direct Holders

Our obligations, as well as the obligations of the trustee and those of any third parties employed by us or the trustee, run only to persons or entities who are the direct holders of debt securities, i.e., those who are registered as holders of debt securities. As noted above, we do not have obligations to you if you hold in street name or

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through other indirect means, either because you choose to hold debt securities in that manner or because we issued the debt securities in the form of global securities as described below. For example, once we make payment to the registered holder, we have no further responsibility for the payment even if that registered holder is legally required to pass the payment along to you as a street name customer but does not do so.

Global Securities

What is a Global Security? A global security is a special type of indirectly held security, as described above under “—Street Name and Other Indirect Holders.” If we choose to issue debt securities in the form of global securities only, the ultimate beneficial owners can only be indirect holders. We do this by requiring that the global security be registered in the name of a financial institution or clearing system, or their nominee, that we select and by requiring that the debt securities included in the global security not be transferred to the name of any other direct holder unless the special circumstances described below occur. The financial institution that acts as the sole direct holder of the global security is called the depository. The Depository Trust Company, New York, New York, known as DTC, may be a depository for one or more series of debt securities. For information regarding DTC, see “—Considerations Relating to DTC.”

Any person wishing to own a debt security included in a global security must do so indirectly by virtue of an account with a broker, bank or other financial institution that in turn has an account with the depository. The prospectus supplement indicates whether we will issue your debt securities only in the form of global securities.

Special Investor Considerations for Global Securities. The account rules of your financial institution and the rules of the depository, as well as general laws relating to securities transfers, will govern your rights as an indirect holder of a global security. We will not recognize you as a registered holder of debt securities and instead will deal only with the depository that holds the global security.

You should be aware that if debt securities are issued only in the form of global securities:

Special Situations When a Global Security will be Terminated. In a few special situations described below, the trustee will terminate the global security and will exchange interests in it for separate certificates representing

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debt securities. After that exchange, the choice of whether to hold debt securities directly or in street name will be up to you. You must consult your own bank or broker to find out how to have your interests in the debt securities transferred to your own name, so that you will be a direct holder. We previously described the rights of street name investors and direct holders in the debt securities in the subsections entitled “—Street Name and Other Indirect Holders” and “—Direct Holders.”

The special situations for termination of a global security are:

The prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular debt securities of the series covered by the prospectus supplement. When a global security terminates, the depository, and not we or the trustee, is responsible for deciding the names of the institutions that will be the initial direct holders. (sections 204 and 305)

Considerations Relating to DTC. DTC has informed us that it is a limited-purpose trust company organized under the New York Banking Law, a “banking organization” within the meaning of the New York Banking Law, a member of the Federal Reserve System, a “clearing corporation” within the meaning of the New York Uniform Commercial Code and a “clearing agency” registered pursuant to the provisions of Section 17A of the Exchange Act. DTC holds securities that DTC participants deposit with DTC. DTC also facilitates the post-trade settlement among DTC participants of securities transactions, such as transfers and pledges in deposited securities through electronic computerized book-entry changes in DTC participants’ accounts, thereby eliminating the need for physical movement of certificates. DTC participants include securities brokers and dealers, banks, trust companies and clearing corporations, and certain other organizations. Indirect access to the DTC system also is available to others such as banks, brokers, dealers, trust companies and clearing corporations that clear through or maintain a custodial relationship with a participant, either directly or indirectly. DTC is a wholly owned subsidiary of The Depository Trust & Clearing Corporation, or DTCC. DTCC is the holding company for DTC, National Securities Clearing Corporation and Fixed Income Clearing Corporation, all of which are registered clearing agencies. DTCC is owned by the users of its regulated subsidiaries. The rules applicable to DTC and DTC participants are on file with the Commission.

Purchases of securities within the DTC system must be made by or through DTC participants, which will receive a credit for the securities on DTC’s records. The ownership interest of each actual purchaser of the notes, which we refer to as the “beneficial owner,” is in turn to be recorded on the DTC participants’ records. Beneficial owners will not receive written confirmation from DTC of their purchase, but beneficial owners are expected to receive written confirmations providing details of the transactions, as well as periodic statements of their holdings from the direct or indirect DTC participant through which the beneficial owner entered into the transaction. Transfers of ownership interests in the global notes will be effected only through entries made on the books of DTC participants acting on behalf of beneficial owners. Beneficial owners will not receive certificates representing their ownership interests in the global notes, except in the event that use of the book-entry system for the notes is discontinued.

To facilitate subsequent transfers, all global securities deposited by direct participants with DTC will be registered in the name of DTC’s partnership nominee, Cede & Co., or such other name as may be requested by an authorized representative of DTC. The deposit of securities with DTC and their registration in the name of Cede & Co. or such other nominee will not change the beneficial ownership of the securities. DTC has no

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knowledge of the actual beneficial owners of the securities. DTC’s records reflect only the identity of the direct participants to whose accounts the securities are credited, which may or may not be the beneficial owners. The participants are responsible for keeping account of their holdings on behalf of their customers.

Conveyance of notices and other communications by DTC to direct participants, by direct participants to indirect participants, and by direct Participants and indirect participants to beneficial owners will be governed by arrangements among them, subject to any statutory or regulatory requirements as may be in effect from time to time.

Redemption notices will be sent to DTC. If less than all of the securities of a particular series are being redeemed, DTC’s practice is to determine by lot the amount of the interest of each direct participant in the securities of such series to be redeemed.

In instances in which a vote is required, generally, neither DTC nor Cede & Co. will itself consent or vote with respect to the securities. Under its usual procedures DTC would mail an omnibus proxy to us as soon as possible after the record date. The omnibus proxy assigns Cede & Co.’s consenting or voting rights to those direct participants to whose accounts such securities are credited on the record date (identified in a listing attached to the omnibus proxy).

Redemption proceeds, distributions and payments on the securities will be made by the trustee to Cede & Co., as nominee of DTC. DTC’s practice is to credit direct participants’ accounts upon DTC’s receipt of funds and corresponding detail information from us on the payment date in accordance with their respective holdings shown on DTC records. Payments by participants to beneficial owners will be governed by standing instructions and customary practices and will be the responsibility of such participants and not of DTC, the trustee or us, subject to any statutory or regulatory requirements as may be in effect from time to time. Payment of redemption proceeds, distributions and dividend payments to Cede & Co. (or such other nominee as may be requested by an authorized representative of DTC) is the responsibility of us or the trustee, disbursement of such payments to direct participants will be the responsibility of DTC, and disbursement of such payments to the beneficial owners will be the responsibility of DTC, and disbursements of such payment to the beneficial owners will be the responsibility of direct and indirect participants.

The information in this section concerning DTC and DTC’s book-entry system has been obtained from sources that we believe to be accurate, but we assume no responsibility for the accuracy thereof. We do not have any responsibility for the performance by DTC or its participants of their respective obligations as described herein or under the rules and procedures governing their respective operations.

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PLAN OF DISTRIBUTION

We may sell debt securities:

The debt securities we distribute by any of these methods may be sold to the public, in one or more transactions, either:

We may sell debt securities from time to time to one or more underwriters, who would purchase the securities as principal for resale to the public, either on a firm-commitment or best-efforts basis. If we sell debt securities to underwriters, we may execute an underwriting agreement with them at the time of sale and will name them in the applicable prospectus supplement. In connection with those sales, underwriters may be deemed to have received compensation from us in the form of underwriting discounts or commissions and may also receive commissions from purchasers of the debt securities for whom they may act as agents. Underwriters may resell the debt securities to or through dealers, and those dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from purchasers for whom they may act as agents. The prospectus supplement will include any required information about underwriting compensation we pay to underwriters, and any discounts, concessions or commissions underwriters allow to participating dealers, in connection with an offering of debt securities.

We may solicit offers to purchase debt securities directly from the public from time to time. We may also designate agents from time to time to solicit offers to purchase debt securities from the public on our behalf. If required, the prospectus supplement relating to any particular offering of debt securities will name any agents designated to solicit offers, and will include information about any commissions we may pay the agents, in that offering. Agents may be deemed to be “underwriters” as that term is defined in the Securities Act.

From time to time, we may sell debt securities to one or more dealers acting as principals. The dealers, who may be deemed to be “underwriters” as that term is defined in the Securities Act, may then resell those debt securities to the public.

Any underwriter or agent involved in the offer and sale of any debt securities will be named in the prospectus supplement.

Underwriters, agents and dealers may be entitled, under agreements with us, to indemnification against certain civil liabilities, including liabilities under the Securities Act.

Each series of debt securities will be a new issue, and there will be no established trading market for any debt security prior to its original issue date. We may, but are not required to, list a particular series of debt securities on a securities exchange or quotation system. Any underwriters to whom we sell debt securities for public offering may make a market in those debt securities. However, no such underwriter that makes a market will be obligated to do so, and any of them may stop doing so at any time without notice. No assurance can be given as to the liquidity or trading market for any of the debt securities.

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Unless otherwise indicated in your prospectus supplement or confirmation of sale, the purchase price of the debt securities will be required to be paid in immediately available funds in New York City.

In connection with an offering, the underwriters may purchase and sell debt securities in the open market. These transactions may include short sales, stabilizing transactions and purchases to cover positions created by short sales. Short sales involve the sale by the underwriters of a greater number of debt securities than they are required to purchase in an offering. Stabilizing transactions consist of certain bids or purchases made for the purpose of preventing or retarding a decline in the market price of the debt securities while an offering is in progress.

The underwriters may also impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the underwriters have repurchased debt securities sold by or for the account of that underwriter in stabilizing or short-covering transactions.

These activities by the underwriters may stabilize, maintain or otherwise affect the market price of the debt securities. As a result, the price of the debt securities may be higher than the price that otherwise might exist in the open market. If these activities are commenced, they may be discontinued by the underwriters at any time. These transactions may be effected on an exchange or automated quotation system, if the debt securities are listed on that exchange or admitted for trading on that automated quotation system, or in the over-the-counter market or otherwise.

Underwriters, dealers and agents may engage in transactions with or perform services for us in the ordinary course of their businesses.

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VALIDITY OF DEBT SECURITIES

Unless otherwise specified in a prospectus supplement, Michael J. Holston, our Executive Vice President and General Counsel, will pass upon the validity of the debt securities for us. As of March 29, 2018, Mr. Holston owned, directly or indirectly, 69,786.227 shares of our common stock, zero shares of restricted stock and options to purchase 344,458 additional shares of our common stock, of which 109,422 were then exercisable.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2017 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND MORE INFORMATION

We are a reporting company under the Exchange Act and file annual, quarterly and current reports, proxy statements and other information with the Commission. You may read and copy any materials filed with the Commission at the Commission’s Public Reference Room at 100 F Street, N.E., Washington, DC 20549. You may obtain information on the operation of the Public Reference Room by calling the Commission at 1-800-SEC-0330. Also, the Commission maintains a website that contains reports, proxy and information statements, and other information regarding issuers, including us, that file electronically with the Commission. The public can obtain any documents that we file electronically with the Commission at the Commission’s website, http://www.sec.gov, or through the New York Stock Exchange, 20 Broad Street, New York, New York 10005, on which our common stock is listed. In addition, you may request copies of these filings at no cost by writing or telephoning us at the following address: Corporate Secretary, Merck & Co., Inc., 2000 Galloping Hill Road, Kenilworth, NJ 07033, (908) 740-4000; or on our website.

We have filed with the Commission a registration statement on Form S-3 relating to the securities covered by this prospectus. This prospectus is a part of the registration statement and does not contain all the information in the registration statement. Whenever a reference is made in this prospectus or any prospectus supplement to a contract or other document filed or incorporated by reference as an exhibit to our registration statement, the reference is only a summary. For a copy of the contract or other document, you should refer to the exhibits that are a part of the registration statement or incorporated by reference into the registration statement by the filing of a Current Report on Form 8-K or otherwise. You may review a copy of the registration statement and the documents we incorporate by reference at the Commission’s Public Reference Room in Washington, D.C., as well as through the Commission’s website as listed above.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The following documents, filed with the Commission (File No. 001-06571) pursuant to the Exchange Act are incorporated by reference in this prospectus: (a) our Annual Report on Form 10-K for the fiscal year ended December 31, 2017; (b) our Proxy Statement on Schedule 14A filed with the Commission on April 10, 2017, to the extent specifically incorporated by reference into Part III of our Annual Report on Form 10-K for the fiscal year ended December 31, 2016; and (c) our Current Reports on Form 8-K filed on January 26, 2018 and February 26, 2018.

Also, all documents filed by us with the Commission under File No. 001-06571 pursuant to Sections 13(a), 13(c), 14, or 15(d) of the Exchange Act (not including Current Reports or portions thereof furnished under Item 2.02 or

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Item 7.01 under Form 8-K) after the date of this prospectus and prior to termination of the relevant offering shall be deemed to be incorporated by reference herein and to be a part hereof from the date of such filing. Any statement contained in a document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes hereof to the extent that a statement contained herein or in any other subsequently filed document that also is, or is deemed to be, incorporated by reference herein modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

We will provide, without charge, copies of any document incorporated by reference into this prospectus, excluding exhibits other than those that are specifically incorporated by reference in this prospectus. You can obtain a copy of any document incorporated by reference by writing or calling us at our principal executive offices as follows:

Merck & Co., Inc.

2000 Galloping Hill Road

Kenilworth, NJ 07033 USA

908-740-1825

Attention: Office of the Secretary

Information on our website is not part of this prospectus, and you should not rely on that information in making your investment decision unless that information is also in this prospectus or has been expressly incorporated by reference into this prospectus.

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$5,000,000,000

Merck & Co., Inc.

$750,000,000 2.900% Notes due 2024

$1,750,000,000 3.400% Notes due 2029

$1,000,000,000 3.900% Notes due 2039

$1,500,000,000 4.000% Notes due 2049

Joint Book-Running Managers

Goldman Sachs & Co. LLC

J.P. Morgan

Morgan Stanley

Citigroup

Co-Managers

Credit Suisse

Mizuho Securities

BBVA

HSBC

Santander

SMBC Nikko

US Bancorp

Wells Fargo Securities

Academy Securities

Blaylock Van, LLC

March 5, 2019