FOURTH AMENDMENT TO COLLABORATIVE RESEARCH, DEVELOPMENT AND LICENSE AGREEMENTS

Exhibit 10.2

***Text Omitted and Filed Separately

with the Securities and Exchange Commission.

Confidential Treatment Requested

Under 17 C.F.R. Sections 200.80(b)(4)

and 240.24b-2.

FOURTH AMENDMENT TO

COLLABORATIVE RESEARCH, DEVELOPMENT

AND LICENSE AGREEMENTS

T HIS F OURTH A MENDMENT TO C OLLABORATIVE R ESEARCH , D EVELOPMENT AND L ICENSE A GREEMENTS (the “Fourth Amendment” ) is entered into as of April 22, 2009 (the “Fourth Amendment Effective Date” ) by and between ACADIA P HARMACEUTICALS I NC . , a Delaware corporation ( “ACADIA” ) with offices at 3911 Sorrento Valley Blvd., San Diego, CA 92121, and A LLERGAN S ALES , LLC , a Delaware limited liability company ( “Allergan” ) with offices at 2525 Dupont Drive, Irvine, CA 92612, and A LLERGAN , I NC ., a Delaware corporation, solely as guarantor of the performance under this Agreement by Allergan.

R ECITALS

W HEREAS , the parties previously entered into that certain Collaborative Research, Development and License Agreement, dated September 24, 1997 (as amended by the First Amendment, the Second Amendment and the Third Amendment described below, the “1997 Agreement” ), pursuant to which the parties conducted collaborative research regarding, among other things, receptor selective compounds with the goal of establishing drug discovery programs related to such receptor selective compounds;

W HEREAS , the parties previously entered into that certain Collaborative Research, Development and License Agreement, dated July 26, 1999 (the “1999 Agreement” ), pursuant to which the parties conducted collaborative research regarding […***…] muscarinic compounds for the treatment or prevention of ocular disease;

W HEREAS , the 1997 Agreement was first amended on March 27, 2003 (the “ First Amendment” ) to continue the collaboration under the 1997 Agreement with respect to alpha adrenergic receptors and on the same date the parties entered into a new Collaborative Research, Development and License Agreement (the “2003 Agreement” ) regarding ACADIA’s chemical-genomics assets;

W HEREAS , the 1997 Agreement and the 2003 Agreement were amended on February 28, 2006 (the “Second Amendment” ) to continue the collaboration under the 1997 Agreement and the 2003 Agreement with respect to alpha adrenergic receptors and to continue to collaborate on other receptor selective compounds included in ACADIA’s chemical-genomics assets;

W HEREAS , the 1997 Agreement and the 2003 Agreement were amended on March 3, 2008 (the “Third Amendment” ) to continue the collaboration under the 1997 Agreement and the 2003 Agreement with respect to alpha adrenergic receptors and to continue to collaborate on muscarinic compounds for eye-care applications;

W HEREAS , the periods for research to be done pursuant to the 1997 Agreement and the 2003 Agreement (together, the “ Agreements ”) will expire on March 27, 2009;

W HEREAS , the parties wish to expand their collaboration on […***…] muscarinic selective compounds for eye-care indications on the terms set forth below; and

W HEREAS , the parties may wish to collaborate on muscarinic selective compounds for eye care indications or on other selective compounds included in ACADIA’s chemical-genomics assets pursuant to the 2003 Agreement and on the terms set forth below.

N OW T HEREFORE , in consideration of the foregoing and the covenants and premises contained in this Fourth Amendment, the parties hereby agree as follows:

1. Alpha Adrenergic Research Program. The parties’ research under the Agreements on alpha adrenergic receptors (the “Alpha Adrenergic Research Program” ) shall cease. The Joint Research Committee shall no longer manage or otherwise concern itself with matters relating to research on alpha adrenergic receptors. The Research Term of the Agreements with respect to the Alpha Adrenergic Research Program expired as of March 27, 2009. Allergan shall retain all of its current exclusive licenses under Section 5.1 of the 1997 Agreement to the ACADIA Technology in the Allergan Field as to alpha adrenergic receptors. For as long as Allergan is continuing to use commercially reasonable efforts to pursue research, development, marketing and/or sale of an Allergan Development Candidate or Allergan Product that is biologically active against an alpha adrenergic receptor, ACADIA shall not, by itself or in collaboration with a third party, use the ACADIA Technology or the Collaboration Technology in the Allergan Field to research compounds, whose primary biological activity is against an alpha adrenergic receptor. (Capitalized terms used in this paragraph that are not defined have the meaning given to them in the 1997 Agreement).

2. […***…] Expansion Program. The parties have agreed on a pool of ten (10) compounds from ACADIA’s library of […***…] muscarinic selective compounds from which Allergan may chose a backup compound (the “ […***…] Expansion Program” ). The current ten (10) compounds are listed on Exhibit A hereto (the “Back-up Pool” ). The Research Term of the Agreements with respect to the […***…] Expansion Program shall be extended to cover the period beginning March 28, 2009 and ending March 27, 2010 (the “Additional Extension Period” ). During the Additional Extension Period, ACADIA will provide information on compounds included in the Back-up Pool for continued evaluation by the parties. Further, if directed by the JRC (as defined below), ACADIA shall engage in the synthesis and evaluation of additional […***…] muscarinic selective compounds. Allergan may remove and add compounds to the Back-up Pool from (a) ACADIA’s existing […***…] muscarinic selective compounds (i.e., those identified prior to the Additional Extension Period), upon mutual agreement of the parties, or (b) from new compounds synthesized at the direction of the JRC, so long as the total number of compounds in the Back-up Pool does not exceed ten (10) at any given time. Allergan may select one compound from the Back-up Pool to be treated as a Collaboration Lead Compound (as defined in the 1999 Agreement and in addition to the compound based on […***…], which has been advanced by the parties pursuant to the 1999 Agreement) pursuant to the terms of the 1999 Agreement. Allergan shall use reasonable efforts to select a compound from the Back-up Pool to be treated as

a second Collaboration Lead Compound prior to the end of the Additional Extension Period. Allergan’s right to so select a compound shall expire at the end of the Additional Extension Period. Upon selecting a compound from the Back-up Pool to be treated as a Collaboration Lead Compound, Allergan shall be entitled to select another compound to add to the Back-up Pool from (a) ACADIA&rsqu