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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934
(Amendment No. )*

SOMAXON PHARMACEUTICALS, INC.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

834453 10 2

(CUSIP Number)

December 31, 2005

(Date of Event Which Requires Filing of this Statement)

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

o Rule 13d-1(b)

o Rule 13d-1(c)

þ Rule 13d-1(d)

* 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 the disclosures provided in a prior cover page.

The information required in 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 (“Act”) 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).

Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: MPM BioVentures III, L.P.

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	Delaware

		5	SOLE VOTING POWER:

NUMBER OF			197,737

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			197,737

WITH:		8	SHARED DISPOSITIVE POWER:

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	197,737

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	1.1%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	PN

Page 2 of 14


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: MPM BioVentures III-QP, L.P.

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	Delaware

		5	SOLE VOTING POWER:

NUMBER OF			2,940,712

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			2,940,712

WITH:		8	SHARED DISPOSITIVE POWER:

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	2,940,712

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	16.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	PN

Page 3 of 14


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: MPM BioVentures III Parallel Fund, LP

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	Delaware

		5	SOLE VOTING POWER:

NUMBER OF			88,832

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			88,832

WITH:		8	SHARED DISPOSITIVE POWER:

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	88,832

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	0.5%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	PN

Page 4 of 14


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: MPM BioVentures III GmbH & Co. Beteiligungs KG

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	Germany

		5	SOLE VOTING POWER:

NUMBER OF			248,504

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			248,504

WITH:		8	SHARED DISPOSITIVE POWER:

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	248,504

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	1.4%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	PN

page 5 of 14


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: MPM Asset Management Investors 2005 BVIII LLC

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	Delaware

		5	SOLE VOTING POWER:

NUMBER OF			52,089

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			52,089

WITH:		8	SHARED DISPOSITIVE POWER:

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	52,089

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	0.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	OO

Page 6 of 14


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: Ansbert Gadicke

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	United States

		5	SOLE VOTING POWER:

NUMBER OF			0

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			3,527,874*

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER:

			3,527,874*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	8,527,874*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	19.6%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	IN


*		Includes 2,940,712 by MPM BioVentures III-QP, L.P. (“BV III QP”), 197,737 by MPM BioVentures III, L.P. (“BV III”), 52,089 by MPM Asset Management Investors 2005 BVIII LLC (“BV AM LLC”), 88,832 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 248,504 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). MPM BioVentures III GP, L.P. (“BV III GP”) and MPM BioVentures III LLC (“BV III LLC”) are the direct and indirect general partners of BV III, BV III QP, BV III PF and BV III KG. The Reporting Person is a member of BV III LLC and BV AM III.

Page 7 of 14


CUSIP No.		834453 10 2


1	NAMES OF REPORTING PERSONS: Luke Evnin

	I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):
	(a) o
	(b) þ

3	SEC USE ONLY:



4	CITIZENSHIP OR PLACE OF ORGANIZATION:

	United States

		5	SOLE VOTING POWER:

NUMBER OF			0

SHARES		6	SHARED VOTING POWER:
BENEFICIALLY
OWNED BY			3,527,874*

EACH		7	SOLE DISPOSITIVE POWER:
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER:

			3,527,874*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON:

	3,527,874*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS):

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9):

	19.6%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS):

	IN


*		Includes 2,940,712 by MPM BioVentures III-QP, L.P. (“BV III QP”), 197,737 by MPM BioVentures III, L.P. (“BV III”), 52,089 by MPM Asset Management Investors 2005 BVIII LLC (“BV AM LLC”), 88,832 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 248,504 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). MPM BioVentures III GP, L.P. (“BV III GP”) and MPM BioVentures III LLC (“BV III LLC”) are the direct and indirect general partners of BV III, BV III QP, BV III PF and BV III KG. The Reporting Person is a member of BV III LLC and BV AM III.

Page 8 of 14

Item 1.

(a)

Name of Issuer

Somaxon Pharmaceuticals, Inc.

(b)

Address of Issuer’s Principal Executive Offices

12750 High Bluff Drive, Suite 310
San Diego, CA 92130

Item 2.

(a)

Name of Person Filing

MPM BioVentures III, L.P.
MPM BioVentures III-QP, L.P.
MPM BioVentures III Parallel Fund, L.P.
MPM BioVentures III GmbH & Co. Beteiligungs KG
MPM Asset Management Investors 2005 BVIII LLC
Ansbert Gadicke
Luke Evnin

(b)

Address of Principal Business Office or, if none, Residence

c/o MPM Capital L.P.
The John Hancock Tower
200 Clarendon Street, 54^th Floor
Boston, MA 02116

(c)

Citizenship

All entities were organized in Delaware, except MPM BioVentures III GmbH & Co. Beteiligungs KG which was organized in Germany. The individuals are United States citizens.

(d)

Title of Class of Securities

Common Stock

(e)

CUSIP Number

834453 10 2


Item 3.		If this statement is filed pursuant to §§240.13d-1(b), or 240.13d-2(b) or (c), check whether the person filing is a:

Not applicable

Page 9 of 14


Item 4.		Ownership

(a)

Amount Beneficially Owned:


MPM BioVentures III, L.P.	197,737
MPM BioVentures III-QP, L.P.	2,940,712
MPM BioVentures III Parallel Fund, L.P.	88,832
MPM BioVentures III GmbH & Co. Beteiligungs KG	248,504
MPM Asset Management Investors 2005 BVIII LLC	52,089
Ansbert Gadicke	3,527,874	*
Luke Evnin	3,527,874	*

Percent of Class:


MPM BioVentures III, L.P.	1.1	%
MPM BioVentures III-QP, L.P.	16.3	%
MPM BioVentures III Parallel Fund, L.P.	0.5	%
MPM BioVentures III GmbH & Co. Beteiligungs KG	1.4	%
MPM Asset Management Investors 2005 BVIII LLC	0.3	%
Ansbert Gadicke	19.6	%
Luke Evnin	19.6	%

(b)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote


MPM BioVentures III, L.P.			197,737
MPM BioVentures III-QP, L.P.			2,940,712
MPM BioVentures III Parallel Fund, L.P.			88,832
MPM BioVentures III GmbH & Co. Beteiligungs KG			248,504
MPM Asset Management Investors 2005 BVIII LLC			52,089
Ansbert Gadicke			0
Luke Evnin			0

Page 10 of 14

(ii)

Shared power to vote or to direct the vote


MPM BioVentures III, L.P.	0
MPM BioVentures III-QP, L.P.	0
MPM BioVentures III Parallel Fund, L.P.	0
MPM BioVentures III GmbH & Co. Beteiligungs KG	0
MPM Asset Management Investors 2005 BVIII LLC	0
Ansbert Gadicke	3,527,874	*
Luke Evnin	3,527,874	*

(iii)

Sole power to dispose or to direct the disposition of


MPM BioVentures III, L.P.			197,737
MPM BioVentures III-QP, L.P.			2,940,712
MPM BioVentures III Parallel Fund, L.P.			88,832
MPM BioVentures III GmbH & Co. Beteiligungs KG			248,504
MPM Asset Management Investors 2005 BVIII LLC			52,089
Ansbert Gadicke			0
Luke Evnin			0

(iv)

Shared power to dispose or to direct the disposition of


MPM BioVentures III, L.P.	0
MPM BioVentures III-QP, L.P.	0
MPM BioVentures III Parallel Fund, L.P.	0
MPM BioVentures III GmbH & Co. Beteiligungs KG	0
MPM Asset Management Investors 2005 BVIII LLC	0
Ansbert Gadicke	3,527,874	*
Luke Evnin	3,527,874	*


*		Includes 2,940,712 by MPM BioVentures III-QP, L.P. (“BV III QP”), 197,737 by MPM BioVentures III, L.P. (“BV III”), 52,089 by MPM Asset Management Investors 2005 BVIII LLC (“BV AM LLC”), 88,832 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 248,504 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). MPM BioVentures III GP, L.P. (“BV III GP”) and MPM BioVentures III LLC (“BV III LLC”) are the direct and indirect general partners of BV III, BV III QP, BV III PF and BV III KG. The Reporting Person is a member of BV III LLC and BV AM III.


Item 5.		Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following o.


Item 6.		Ownership of More than Five Percent on Behalf of Another Person

Not Applicable

Page 11 of 14


Item 7.		Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person.

Not Applicable


Item 8.		Identification and Classification of Members of the Group

Not Applicable


Item 9.		Notice of Dissolution of a Group

Not Applicable


Item 10.		Certification

Not Applicable

Page 12 of 14

SIGNATURE

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: February 9, 2006


MPM BIOVENTURES III, L.P.		MPM BIOVENTURES III-QP, L.P.

By:	MPM BioVentures III GP, L.P., its General Partner	By:	MPM BioVentures III GP, L.P., its General Partner

By:	MPM BioVentures III LLC, its General Partner	By:	MPM BioVentures III LLC, its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin

	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM BIOVENTURES III PARALLEL FUND,L.P.		MPM BIOVENTURES III GMBH & CO. BETEILIGUNGS KG

By:	MPM BioVentures III GP, L.P., its General Partner	By:	MPM BioVentures III GP, L.P., in its capacity as the Managing Limited Partner

By:	MPM BioVentures III LLC, its General Partner	By:	MPM BioVentures III LLC, its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin

	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM ASSET MANAGEMENT INVESTORS 2005 BVIII LLC

By:	/s/ Luke Evnin	By:	/s/ Ansbert Gadicke

	Name: Luke Evnin		Name: Ansbert Gadicke
	Title: Manager

By:	/s/ Luke Evnin

	Name: Luke Evnin

Attention: Intentional misstatements or omissions of fact constitute Federal criminal violations (See 18 U.S.C. 1001)

Page 13 of 14

EXHIBIT A

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of Somaxon Pharmaceuticals, Inc. and further agree that this agreement be included as an exhibit to such filing. Each party to the agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement. Each party to this agreement agrees that this joint filing agreement may be signed in counterparts.

In evidence whereof, the undersigned have caused this Agreement to be executed on their behalf this 9^th day of February, 2006.


MPM BIOVENTURES III, L.P.		MPM BIOVENTURES III-QP, L.P.

By:	MPM BioVentures III GP, L.P., its General Partner	By: MPM	BioVentures III GP, L.P., its General Partner

By:	MPM BioVentures III LLC, its General Partner	By: MPM	BioVentures III LLC, its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin

	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM BIOVENTURES III PARALLEL FUND, L.P.		MPM BIOVENTURES III GMBH & CO. BETEILIGUNGS KG

By:	MPM BioVentures III GP, L.P., its General Partner	By:	MPM BioVentures III GP, L.P., in its capacity as the Managing Limited Partner

By:	MPM BioVentures III LLC, its General Partner	By:	MPM BioVentures III LLC, its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin

	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM ASSET MANAGEMENT INVESTORS 2005 BVIII LLC

By:	/s/ Luke Evnin	By:	/s/ Ansbert Gadicke

	Name: Luke Evnin		Name: Ansbert Gadicke
	Title: Manager

By:	/s/ Luke Evnin

	Name: Luke Evnin

Page 14 of 14