UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                  SCHEDULE 13G

                   Under the Securities Exchange Act of 1934
                               (Amendment No. 1)*

                            ADVANCED MAGNETICS, INC.
--------------------------------------------------------------------------------
                                (Name of Issuer)

                    Common Stock, $0.01 Par Value Per Share
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                   00753P103
                                   ---------
                                 (CUSIP Number)

                                December 31, 2006
                                -----------------
                      (Date of Event which Requires Filing
                               of this Statement)



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

                  [ ]      Rule 13d-1(b)
                  [X]      Rule 13d-1(c)
                  [ ]      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 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 ("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).


                                  Page 1 of 8





--------------------------------                              ------------------
CUSIP No. 00753P103                       13G                 Page 2 of 8 Pages
--------------------------------                              ------------------

---------- ---------------------------------------------------------------------
1          NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           CR Intrinsic Investors, LLC
---------- ---------------------------------------------------------------------
2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                  (a) [ ]
                                                                  (b) [X]
---------- ---------------------------------------------------------------------
3          SEC USE ONLY
---------- ---------------------------------------------------------------------
4          CITIZENSHIP OR PLACE OF ORGANIZATION

           Delaware
-------------------- ------ ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0
                     ------ ----------------------------------------------------
NUMBER OF SHARES         6  SHARED VOTING POWER
BENEFICIALLY OWNED
BY EACH REPORTING           0 (see Item 4)
PERSON WITH          ------ ----------------------------------------------------
                     7      SOLE DISPOSITIVE POWER

                            0
                     ------ ----------------------------------------------------
                     8      SHARED DISPOSITIVE POWER

                            0 (see Item 4)
---------- ---------------------------------------------------------------------
9          AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           0  (see Item 4)
---------- ---------------------------------------------------------------------
10         CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

           [ ]
---------- ---------------------------------------------------------------------
11         PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           0%  (see Item 4)
---------- ---------------------------------------------------------------------
12         TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 2 of 8


--------------------------------                              ------------------
CUSIP No. 00753P103                       13G                 Page 3 of 8 Pages
--------------------------------                              ------------------

---------- ---------------------------------------------------------------------
1          NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Sigma Capital Management, LLC
---------- ---------------------------------------------------------------------
2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                  (a) [ ]
                                                                  (b) [X]
---------- ---------------------------------------------------------------------
3          SEC USE ONLY
---------- ---------------------------------------------------------------------
4          CITIZENSHIP OR PLACE OF ORGANIZATION

           Delaware
-------------------- ------ ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0
                     ------ ----------------------------------------------------
NUMBER OF SHARES         6  SHARED VOTING POWER
BENEFICIALLY OWNED
BY EACH REPORTING           0 (see Item 4)
PERSON WITH          ------ ----------------------------------------------------
                     7      SOLE DISPOSITIVE POWER

                            0
                     ------ ----------------------------------------------------
                     8      SHARED DISPOSITIVE POWER

                            0 (see Item 4)
---------- ---------------------------------------------------------------------
9          AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           0  (see Item 4)
---------- ---------------------------------------------------------------------
10         CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

           [ ]
---------- ---------------------------------------------------------------------
11         PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           0%  (see Item 4)
---------- ---------------------------------------------------------------------
12         TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 3 of 8


--------------------------------                              ------------------
CUSIP No. 00753P103                       13G                 Page 4 of 8 Pages
--------------------------------                              ------------------

---------- ---------------------------------------------------------------------
1          NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Steven A. Cohen
---------- ---------------------------------------------------------------------
2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                  (a) [ ]
                                                                  (b) [X]
---------- ---------------------------------------------------------------------
3          SEC USE ONLY
---------- ---------------------------------------------------------------------
4          CITIZENSHIP OR PLACE OF ORGANIZATION

           United States
-------------------- ------ ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0
                     ------ ----------------------------------------------------
NUMBER OF SHARES         6  SHARED VOTING POWER
BENEFICIALLY OWNED
BY EACH REPORTING           0 (see Item 4)
PERSON WITH          ------ ----------------------------------------------------
                     7      SOLE DISPOSITIVE POWER

                            0
                     ------ ----------------------------------------------------
                     8      SHARED DISPOSITIVE POWER

                            0 (see Item 4)
---------- ---------------------------------------------------------------------
9          AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           0  (see Item 4)
---------- ---------------------------------------------------------------------
10         CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

           [ ]
---------- ---------------------------------------------------------------------
11         PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           0%  (see Item 4)
---------- ---------------------------------------------------------------------
12         TYPE OF REPORTING PERSON*

           IN
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 4 of 8




Item 1(a)           Name of Issuer:
                    --------------

                    Advanced Magnetics, Inc.

Item 1(b)           Address of Issuer's Principal Executive Offices:
                    -----------------------------------------------

                    125 Cambridge Park Drive-6th Floor
                    Cambridge, MA  02140

Items 2(a)          Name of Person Filing:
                    ---------------------

                    This statement is filed by: (i) CR Intrinsic Investors, LLC
                    ("CR Intrinsic Investors") with respect to shares of common
                    stock, par value $0.01 per share ("Shares"), of the Issuer
                    beneficially owned by CR Intrinsic Investments, LLC ("CR
                    Intrinsic Investments"); (ii) Sigma Capital Management, LLC
                    ("Sigma Management") with respect to Shares beneficially
                    owned by Sigma Capital Associates, LLC ("Sigma Capital
                    Associates") and (iii) Steven A. Cohen with respect to
                    Shares beneficially owned by CR Intrinsic Investors, CR
                    Intrinsic Investments, Sigma Management and Sigma Capital
                    Associates.

                    CR Intrinsic Investors, Sigma Management and Steven A. Cohen
                    have entered into a Joint Filing Agreement, a copy of which
                    is filed with this Schedule 13G as Exhibit 99.1, pursuant to
                    which they have agreed to file this Schedule 13G jointly in
                    accordance with the provisions of Rule 13d-1(k) of the
                    Securities Exchange Act of 1934, as amended.

Item 2(b)           Address of Principal Business Office:
                    ------------------------------------

                    The address of the principal business office of (i) CR
                    Intrinsic Investors and Mr. Cohen is 72 Cummings Point Road,
                    Stamford, Connecticut 06902 and (ii) Sigma Management is 540
                    Madison Avenue, New York, New York 10022.

Item 2(c)           Citizenship:
                    -----------

                    CR Intrinsic Investors and Sigma Management are Delaware
                    limited liability companies. Mr. Cohen is a United States
                    citizen.

Item 2(d)           Title of Class of Securities:
                    ----------------------------

                    Common Stock, par value $0.01 per share

                                  Page 5 of 8


Item 2(e)           CUSIP Number:
                    ------------

                    00753P103

Item 3              Not Applicable

Item 4              Ownership:
                    ---------

                    The percentages used herein are calculated based upon the
                    Shares issued and outstanding as of November 15, 2006 as
                    reported on the Issuer's annual report on Form 10-K filed
                    with the Securities and Exchange Commission by the Issuer
                    for the fiscal year ended September 30, 2006.

                    As of the close of business on December 31, 2006:

                    1. CR Intrinsic Investors, LLC
                    (a)    Amount beneficially owned: -0-
                    (b)    Percent of class: 0%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii)   Shared power to vote or direct the vote: -0-
                    (iii)  Sole power to dispose or direct the disposition: -0-
                    (iv)   Shared power to dispose or direct the disposition:
                           -0-

                    2. Sigma Capital Management, LLC
                    (a)    Amount beneficially owned: -0-
                    (b)    Percent of class: 0%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii)   Shared power to vote or direct the vote: -0-
                    (iii)  Sole power to dispose or direct the disposition: -0-
                    (iv)   Shared power to dispose or direct the disposition:
                           -0-

                    3. Steven A. Cohen
                    (a)    Amount beneficially owned: -0-
                    (b)    Percent of class: 0%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii)   Shared power to vote or direct the vote: -0-
                    (iii)  Sole power to dispose or direct the disposition: -0-
                    (iv)   Shared power to dispose or direct the disposition:
                           -0-

                    Mr. Cohen controls each of CR Intrinsic Investors and Sigma
                    Management. Each of CR Intrinsic Investors, Sigma Management
                    and Mr. Cohen disclaim beneficial ownership of any of the
                    securities covered by this statement.

                                  Page 6 of 8


 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.  [X]

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

                    Not Applicable

Item 7              Identification and Classification of the
                    ----------------------------------------
                    Subsidiary Which Acquired the Security Being
                    --------------------------------------------
                    Reported on By the Parent Holding Company:
                    -----------------------------------------

                    Not Applicable

Item 8              Identification and Classification of Members
                    ---------------------------------------------
                    of the Group:
                    ------------

                    Not Applicable

Item 9              Notice of Dissolution of Group:
                    ------------------------------

                    Not Applicable

Item 10             Certification:
                    -------------

     By signing below the signatory certifies that, to the best of his 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.

                                  Page 7 of 8



                                    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 14, 2007


CR INTRINSIC INVESTORS, LLC


By:  /s/ Peter Nussbaum
    -----------------------------------------
Name:  Peter Nussbaum
Title: Authorized Person


SIGMA CAPITAL MANAGEMENT, LLC


By:  /s/ Peter Nussbaum
    -----------------------------------------
Name:  Peter Nussbaum
Title: Authorized Person


STEVEN A. COHEN


By:  /s/ Peter Nussbaum
    -----------------------------------------
Name:  Peter Nussbaum
Title: Authorized Person

                                  Page 8 of 8