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)

                           ARENA PHARMACEUTICALS INC.
           -------------------------------------------------------------
                                (Name of Issuer)

                                  COMMON STOCK
           -------------------------------------------------------------
                         (Title of Class of Securities)

                                   040047 10 2
           -------------------------------------------------------------
                                 (CUSIP Number)

                                December 31, 2001
           -------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)



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

[ ]        Rule 13d-1(b)

[ ]        Rule 13d-1(c)

[X]        Rule 13d-1(d)




/1/ The remainder of this cover page shall be filled out for a reporting
person's initial filing on this 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 (the "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).




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CUSIP NO.    040047 10 2            13G           Page    2    of    5    Pages
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--------- ----------------------------------------------------------------------
   1      NAME OF REPORTING PERSON
          S.S. or I.R.S. Identification No. Of Above Person

          Ansbert Gadicke

--------- ----------------------------------------------------------------------
   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

-------------------------------- ------ ----------------------------------------
           NUMBER OF               5    SOLE VOTING POWER
     SHARES BENEFICIALLY                2,074,792 (1)
           OWNED BY
             EACH                ------ ----------------------------------------
       REPORTING PERSON            6    SHARED VOTING POWER
             WITH                       None

                                 ------ ----------------------------------------
                                   7    SOLE DISPOSITIVE POWER
                                        2,074,792 (1)

                                 ------ ----------------------------------------
                                   8    SHARED DISPOSITIVE POWER
                                        None

--------- ----------------------------------------------------------------------
   9      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
           2,074,792 (1)

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

--------- ----------------------------------------------------------------------
   11     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
          7.52%

--------- ----------------------------------------------------------------------
   12     TYPE OF REPORTING PERSON*
          IN

--------- ----------------------------------------------------------------------
         *SEE INSTRUCTIONS BEFORE FILLING OUT!




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CUSIP NO.    040047 10 2            13G           Page    3    of    5    Pages
             -----------                              ---------  ---------
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Item 1 (a).       Name of Issuer:

       Arena Pharmaceuticals Inc.
       -------------------------------------------------------------------------

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

       6166 Nancy Ridge Drive, San Diego, CA 92121
       -------------------------------------------------------------------------

Item 2(a).        Name of Person Filing:

       Ansbert Gadicke
       -------------------------------------------------------------------------

Item 2(b).        Address of Principal Business Office or, if none, Residence:

       c/o MPM Capital L.P., 111 Huntington Avenue, 31st floor, Boston, MA 02199
       -------------------------------------------------------------------------

Item 2(c).        Citizenship:

       United States
       -------------------------------------------------------------------------

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

       Common Stock
       -------------------------------------------------------------------------

Item 2(e).        CUSIP Number:

       040047 10 2
       -------------------------------------------------------------------------

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 a:

   (a) [ ] Broker or dealer registered under Section 15 of the Exchange Act,

   (b) [ ] Bank as defined in Section 3(a)(6) of the Exchange Act,

   (c) [ ] Insurance company as defined in Section 3(a)(19) of the Exchange Act,

   (d) [ ] Investment company registered under Section 8 of the Investment
           Company Act,

   (e) [ ] An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E),

   (f) [ ] An employee benefit plan or endowment fund in accordance with
           Rule 13d-1(b)(1)(ii)(F),

   (g) [ ] A parent holding company or control person, in accordance with
           Rule 13d-1(b)(1)(ii)(G),

   (h) [ ] A savings association as defined in Section 3(b) of the Federal
           Deposit Insurance Act,

   (i) [ ] A church plan that is excluded from the definition of an investment
           company under Section 3(c)(14) of the Investment Company Act,

   (j) [ ] Group, in accordance with Rule 13d-1(b)(1)(ii)(J).




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CUSIP NO.    040047 10 2            13G           Page    4    of    5    Pages
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Item 4.  Ownership.

   (a) Amount beneficially owned:

       2,074,792 (1)
       -------------------------------------------------------------------------

   (b) Percent of class:

       7.52%
       -------------------------------------------------------------------------

   (c) Number of shares as to which such person has:

       (i)   sole power to vote or to direct the vote  2,074,792 (1)
                                                       -------------
       (ii)  shared power to vote or to direct the vote  None
                                                         ----
       (iii) sole power to dispose or to direct the disposition of 2,074,792 (1)
                                                                   -------------
       (iv)  shared power to dispose or to direct the disposition of  None
                                                                      ----

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

           Not applicable
           ---------------------------------------------------------------------

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

           Various persons have the right to receive or the power to direct the
           receipt of dividends from, or the proceeds from the sale of, the
           shares to which this statement relates. No one person's interest in
           such shares is more than five percent of the total outstanding stock
           of the Issuer.
           ---------------------------------------------------------------------

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.   Certifications.

           Not applicable
           ---------------------------------------------------------------------

(1) Includes shares held through interests in MPM Capital L.P. ("MPM Capital")
and in entities directly or indirectly controlled by it. MPM Capital is a direct
or indirect parent and or a control person of MPM Asset Management LLC and funds
managed or advised by it and the general partners of such funds. Also includes
shares held through interests in Medical Portfolio Management LLC, the general
partner of MPM Capital. Among the shares included, 1,796,035 shares are held by
BB BioVentures L.P.; 257,172 shares are held by MPM BioVentures Parallel Fund,
L.P.; and 21,585 shares are held by MPM Asset Management Investors 1998 LLC.
Each reporting person herein disclaims beneficial ownership of shares not
directly held by such reporting person.




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CUSIP NO.    040047 10 2            13G           Page    5    of    5    Pages
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                                    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.

                                                  February 13, 2002
                                           -------------------------------------
                                                         Date

                                                /s/ Ansbert Gadicke
                                           -------------------------------------
                                                       Signature

                                                    Ansbert Gadicke
                                           -------------------------------------
                                                       Name/Title