QuickLinks -- Click here to rapidly navigate through this document

SECURITIES AND EXCHANGE COMMISSION
Washington, DC 20549



SCHEDULE 13G
(Rule 13d-102)

        INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
TO RULES 13d-1(b) (c) AND (d) AND AMENDMENTS THERETO FILED
PURSUANT TO 13d-2(b)
(Amendment No.    )1

Insmed Incorporated
(Name of Issuer)

Common Stock
(Title of Class of Securities)

457669 20 8
(CUSIP Number)

September 19, 2002
(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:


1        The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).





CUSIP NO. 457669 20 8
  13G  
Page 2 of 9 Pages

1 NAME OF REPORTING PERSON:
Biotechnology Value Fund, L.P.
   

 

I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):

 

 

2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*    
      (a) ý
      (b) o

3 SEC USE ONLY    

 

 

 

 

4 CITIZENSHIP OR PLACE OF ORGANIZATION    

 

Delaware

 

 

    5   SOLE VOTING POWER
NUMBER OF       0
SHARES  
BENEFICIALLY   6   SHARED VOTING POWER
OWNED       630,070
BY  
EACH   7   SOLE DISPOSITIVE POWER
REPORTING       0
PERSON  
WITH   8   SHARED DISPOSITIVE POWER
        630,070

9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON    

 

630,070

 

 

10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*    

 

 

 

o

11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9    

 

1.9%

 

 

12 TYPE OF REPORTING PERSON*    

 

PN

 

 


* SEE INSTRUCTIONS BEFORE FILLING OUT!

 

 

 

 


CUSIP NO. 457669 20 8
  13G  
Page 3 of 9 Pages

1 NAME OF REPORTING PERSON:
Biotechnology Value Fund II, L.P.
   

 

I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):

 

 

2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*    
      (a) ý
      (b) o

3 SEC USE ONLY    

 

 

 

 

4 CITIZENSHIP OR PLACE OF ORGANIZATION    

 

Delaware

 

 

    5   SOLE VOTING POWER
NUMBER OF       0
SHARES  
BENEFICIALLY   6   SHARED VOTING POWER
OWNED       426,500
BY  
EACH   7   SOLE DISPOSITIVE POWER
REPORTING       0
PERSON  
WITH   8   SHARED DISPOSITIVE POWER
        426,500

9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON    

 

426,500

 

 

10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*    

 

 

 

o

11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9    

 

1.3%

 

 

12 TYPE OF REPORTING PERSON*    

 

PN

 

 


* SEE INSTRUCTIONS BEFORE FILLING OUT!

 

 

 

 


CUSIP NO. 457669 20 8
  13G  
Page 4 of 9 Pages

1 NAME OF REPORTING PERSON:
BVF Investments, L.L.C.
   

 

I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):

 

 

2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*    
      (a) ý
      (b) o

3 SEC USE ONLY    

 

 

 

 

4 CITIZENSHIP OR PLACE OF ORGANIZATION    

 

Delaware

 

 

    5   SOLE VOTING POWER
NUMBER OF       0
SHARES  
BENEFICIALLY   6   SHARED VOTING POWER
OWNED       994,500
BY  
EACH   7   SOLE DISPOSITIVE POWER
REPORTING       0
PERSON  
WITH   8   SHARED DISPOSITIVE POWER
        994,500

9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON    

 

994,500

 

 

10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*    

 

 

 

o

11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9    

 

3.0%

 

 

12 TYPE OF REPORTING PERSON*    

 

OO

 

 


* SEE INSTRUCTIONS BEFORE FILLING OUT!

 

 

 

 


CUSIP NO. 457669 20 8
  13G  
Page 5 of 9 Pages

1 NAME OF REPORTING PERSON:
BVF Partners L.P.
   

 

I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):

 

 

2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*    
      (a) ý
      (b) o

3 SEC USE ONLY    

 

 

 

 

4 CITIZENSHIP OR PLACE OF ORGANIZATION    

 

Delaware

 

 

    5   SOLE VOTING POWER
NUMBER OF       0
SHARES  
BENEFICIALLY   6   SHARED VOTING POWER
OWNED       2,138,070
BY  
EACH   7   SOLE DISPOSITIVE POWER
REPORTING       0
PERSON  
WITH   8   SHARED DISPOSITIVE POWER
        2,138,070

9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON    

 

2,138,070

 

 

10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*    

 

 

 

o

11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9    

 

6.5%

 

 

12 TYPE OF REPORTING PERSON*    

 

PN

 

 


* SEE INSTRUCTIONS BEFORE FILLING OUT!

 

 

 

 


CUSIP NO. 457669 20 8
  13G  
Page 6 of 9 Pages

1 NAME OF REPORTING PERSON:
BVF Inc.
   

 

I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):

 

 

2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*    
      (a) ý
      (b) o

3 SEC USE ONLY    

 

 

 

 

4 CITIZENSHIP OR PLACE OF ORGANIZATION    

 

Delaware

 

 

    5   SOLE VOTING POWER
NUMBER OF       0
SHARES  
BENEFICIALLY   6   SHARED VOTING POWER
OWNED       2,138,070
BY  
EACH   7   SOLE DISPOSITIVE POWER
REPORTING       0
PERSON  
WITH   8   SHARED DISPOSITIVE POWER
        2,138,070

9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON    

 

2,138,070

 

 

10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*    

 

 

 

o

11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9    

 

6.5%

 

 

12 TYPE OF REPORTING PERSON*    

 

IA, CO

 

 


* SEE INSTRUCTIONS BEFORE FILLING OUT!

 

 

 

 


CUSIP NO. 457669 20 8
  13G  
Page 7 of 9 Pages


ITEM 1(a). NAME OF ISSUER:


ITEM 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES:


ITEM 2(a). NAME OF PERSON FILING:


ITEM 2(b). ADDRESS OF PRINCIPAL BUSINESS OFFICE:


ITEM 2(c). CITIZENSHIP:

BVF:   a Delaware limited partnership
BVF2:   a Delaware limited partnership
Investments:   a Delaware limited liability company
Partners:   a Delaware limited partnership
BVF Inc.:   a Delaware corporation


ITEM 2(d). TITLE OF CLASS OF SECURITIES:


ITEM 2(e). CUSIP Number:



CUSIP NO. 457669 20 8
  13G  
Page 8 of 9 Pages


ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO RULE 13d-1(b), or 13d-2(b) or (c) CHECK WHETHER
                THE PERSON FILING IS: One of the following


ITEM 4. OWNERSHIP:


ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS:


ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON:


ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
                SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY:


ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF A GROUP:


ITEM 9. NOTICE OF DISSOLUTION OF GROUP:



CUSIP NO. 457669 20 8
  13G  
Page 9 of 9 Pages


ITEM 10. CERTIFICATION

        By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

        After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated:  September 27, 2002          
           
    BIOTECHNOLOGY VALUE FUND, L.P.
           
    By: BVF Partners L.P., its general partner
           
      By: BVF Inc., its general partner
           
        By: /s/  MARK N. LAMPERT      
Mark N. Lampert
President
           
    BIOTECHNOLOGY VALUE FUND II, L.P.
           
    By: BVF Partners L.P., its general partner
           
      By: BVF Inc., its general partner
           
        By: /s/  MARK N. LAMPERT      
Mark N. Lampert
President
           
    BVF INVESTMENTS, L.L.C.
           
    By: BVF Partners L.P., its manager
           
      By: BVF Inc., its general partner
           
        By: /s/  MARK N. LAMPERT      
Mark N. Lampert
President
           
    BVF PARTNERS L.P.
           
    By: BVF Inc., its general partner
           
      By: /s/  MARK N. LAMPERT      
Mark N. Lampert
President
           
    BVF INC.
           
    By: /s/  MARK N. LAMPERT      
Mark N. Lampert
President



QuickLinks

SCHEDULE 13G
ITEM 1(a). NAME OF ISSUER
ITEM 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES
ITEM 2(a). NAME OF PERSON FILING
ITEM 2(b). ADDRESS OF PRINCIPAL BUSINESS OFFICE
ITEM 2(c). CITIZENSHIP
ITEM 2(d). TITLE OF CLASS OF SECURITIES
ITEM 2(e). CUSIP Number
ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO RULE 13d-1(b), or 13d-2(b) or (c) CHECK WHETHER THE PERSON FILING IS: One of the following
ITEM 4. OWNERSHIP
ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS
ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON
ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY
ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF A GROUP
ITEM 9. NOTICE OF DISSOLUTION OF GROUP
ITEM 10. CERTIFICATION