Exhibit 10.7  SECOND
AMENDMENT TO RESEARCH
COLLABORATION AND LICENSE AGREEMENT  This
SECOND AMENDMENT TO RESEARCH COLLABORATION AND LICENSE AGREEMENT (this Second
Amendment) dated as of February 20, 2007,
is entered into by and between Merck & Co., Inc. (MERCK) and ARENA
PHARMACEUTICALS, INC., (ARENA) and amends that certain Research Collaboration
and License Agreement between MERCK and ARENA, effective as of October 21,
2002, as subsequently amended by the First Amendment to the Research
Collaboration and License Agreement between MERCK and ARENA, dated October 20,
2004 (as so amended, the Agreement).  MERCK
and ARENA, for good and valuable consideration, the receipt and sufficiency of
which are hereby mutually acknowledged, and intending to be legally bound
hereby, agree as follows:  1DEFINITIONS
AND GENERAL TERMS  1.1           All capitalized terms used and not defined in this Second
Amendment shall have the meaning as set out in the Agreement.  1.2           The term Effective Date of this Second Amendment shall be
February 20, 2007.  1.3           Except as modified by this Second
Amendment, the terms of the Agreement shall continue in full force and effect
without modification.  1.4           Notwithstanding anything else to the
contrary in this Second Amendment, this Second Amendment shall not be effective
unless and until the transactions contemplated by the Common Stock Purchase
Agreement dated February 20, 2007, by and between MERCK and ARENA shall
have closed.  2AMENDMENTS TO THE AGREEMENT  As
of the Effective Date of this Second Amendment, the Parties amend the Agreement
as follows:  4.1           Section 2.2(e) of the Agreement is deleted in
its entiretyand replaced with the following:  (e)From the second anniversary
date of the Effective Date until February 20, 2007, ARENA shall dedicate
nineteen (19) FTEs to the Program to work directly and exclusively on the
Program, and MERCK will provide funding for that number of FTEs at the Annual
FTE Rate.  From February 21, 2007
until October 21, 2007, ARENA shall dedicate fourteen (14) FTEs to the
Program to work directly and exclusively on the Program, and MERCK will provide
funding for that number of FTEs at the Annual FTE Rate.  The JRC is entitled to modify the number of


ARENA
FTEs dedicated to the Program, if such decision is unanimous.  For clarity, Merck shall not be entitled to
unilaterally change the number of ARENA FTEs dedicated to the Program and
funded by MERCK that would result in a reduction of FTEs.  This Second Amendment may
be executed in any number of counterparts, each of which shall be an original,
but all of which together shall constitute one instrument.  [Signatures on following page]  2


IN
WITNESS WHEREOF, each of the Parties has caused this Second Amendment to be
duly executed in the name of and on its behalf, as of the Effective Date of
this Second Amendment.   ARENA  PHARMACEUTICALS, INC.
  
  
  MERCK &
  CO., INC.By:
  /s/
  Jack Lief
  
  By:
  /s/
  Judy C. LewentName:
  Jack Lief
  
  
  Name:
  Judy C. LewentTitle:
  President and CEO
  
  
  Title:
  Executive VP and CFOFebruary 20,
  2007
  
  
  February 20,
  2007Date
  
  
  Date  3