<PAGE>


                                                                   EXHIBIT 10.2

CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                     AGREEMENT

     THIS AGREEMENT (the "Agreement") is made this 8th day of January, 1998, 
by and between CoCensys, Inc., a Delaware corporation ("CoCensys"), located 
at 201 Technology Drive, Irvine, California 92618, and Warner-Lambert 
Company, a Delaware corporation ("Warner"), located at 201 Tabor Road, Morris 
Plains, New Jersey 07950.

                                      RECITALS
                                          
     a.   The parties entered into that certain amended and restated 
Research, Development and Marketing Collaboration Agreement dated October 13, 
1997, (the "Collaboration Agreement"), pursuant to which the parties 
determined to collaborate in efforts to develop and discover NMDA receptor 
sub-type selective antagonists and AMPA-type glutamate receptor antagonists.

     b.   The parties have determined that a collaboration in the area of 
AMPA antagonists would not be beneficial to the parties at this point in time 
and desire to amend the Collaboration Agreement to terminate the AMPA 
collaboration and add certain key man provisions.

     NOW, THEREFORE, in consideration of the foregoing premises and the 
mutual promises, covenants and conditions contained herein, CoCensys and 
Warner hereby agree as follows:

     All capitalized terms used herein shall have the meanings given to them 
in the Collaboration Agreement.

     1.   The Collaboration Agreement is hereby amended to add the following as
a new Section 14.6:
     
     "14.6 Key Personnel. CoCensys shall use its best efforts to ensure that [*]
     oversees the Research Program on behalf of CoCensys and that [*] devotes no
     less than [*] of his time in also overseeing [*] and CoCensys' efforts
     relating to the Research Program.  In the event that on or before the end 
     of the term of the Research Program, (A) [*] (i) is physically and mentally
     capable of overseeing CoCensys' work under the Research Plan but (ii) for 
     any reason fails to oversee such work, or (B) [*] (y) is physically and 
     mentally capable of devoting [*] of his time to overseeing CoCensys' work 
     under the research plan but (z) for any reason fails to

                                       1

* Confidential treatment requested
<PAGE>



 
     devote such time to such work, then in the case of either (A) or (B), 
     CoCensys shall immediately notify Warner thereof and CoCensys will have 
     up to [*] after such failure by either [*] to hire a replacement for [*],
     as the case may be (the "Search Period"). By notice delivered to 
     CoCensys during the [*] period after the end of the Search Period, 
     Warner may voluntarily terminate the Term of the Research Program, 
     effective [*] after the end of the Search Period, if in its reasonable 
     scientific opinion or for other reasonable commercial concerns relating 
     to the conduct of the Research Program it does not approve of the 
     replacement for [*] hired by CoCensys, then the Term of the Research 
     Program shall end [*] following the end of the Search Period.  
     Termination of the Research Program pursuant to the previous sentence 
     shall be deemed an ordinary termination of the Term of the Research 
     Program under the first sentence of Section 2.4 and shall not be deemed 
     early termination upon the election of a party under the second sentence 
     of Section 2.4 or termination for breach under Section 14.1.  Warner 
     will be required to make any research funding payments that are required 
     under Section 2.2 that come due on or before the effective date of such 
     termination, and CoCensys will continue to be obligated to perform its 
     duties under the Research Program during the Term of the Research 
     Program.  Warner agrees that during the Term of the Research Program it 
     shall not solicit for employment or employ [*], or otherwise interfere 
     with the employment by CoCensys of [*] with the intent of ending such 
     employment."

     2.   The parties shall in good faith negotiate an amendment to the 
Collaboration Agreement pursuant to which that portion of the Research 
Program devoted to AMPA antagonists will be terminated.  As of the date of 
this Agreement, the parties shall no longer be obligated to perform any work 
under the Research Program or exchange any further research results related 
to AMPA antagonists.

     3.   Section 2.2 of the Collaboration Agreement shall be amended to 
provide that commencing [*], CoCensys shall only be obligated to provide a 
minimum of [*]Scientific FTEs, to be funded by Warner at a rate of [*] per 
Scientific FTE per calendar year.  Section 2.2 shall further be amended to 
provide that in the event Warner determines that the number of Scientific 
FTEs for [*] must be increased, up to a maximum of [*], Warner shall notify 
CoCensys by [*], and CoCensys shall be obligated to provide such FTEs, to be 
funded by Warner, at the reimbursement rates set forth above.  Under all 
circumstances, Warner shall be obligated to fund a minimum of [*] Scientific 
FTEs commencing [*].

     4.   CoCensys hereby agrees that on January 9, 1999, CoCensys shall 
issue to Warner such number of shares of common stock of CoCensys which shall 
equal $1,000,000.00 divided by the "Average Trading Price".  The "Average 
Trading Price" shall be the average of the closing prices of CoCensys common 
stock (as reported in THE WALL STREET JOURNAL, western edition) for the 
thirty (30) "Trading Days" prior to January 9, 1999.  The term "Trading Day" 
shall mean any day on which shares of CoCensys' common stock have been traded 
on a national securities exchange, the NASDAQ stock market or otherwise, as 
reported in THE WALL STREET JOURNAL, western edition.  Subject to 
circumstances beyond CoCensys' reasonable control, CoCensys shall cause such 
shares to

                                       2

* Confidential treatment requested
<PAGE>

be immediately tradable on any securities exchange on which CoCensys' shares 
are then traded (whether by registration or exemption).

     5.   The parties further agree that they shall execute such other 
documents and instruments as may be necessary to effectuate the transactions 
contemplated herein.

     6.   Except as otherwise set forth herein or as subsequently agreed to 
by the parties in the good faith negotiations discussed herein, the terms of 
the amended and restated Research, Development and Marketing Collaboration 
Agreement shall remain unchanged and in full force and effect.

     IN WITNESS WHEREOF, the parties have hereunto set their hands as of the 
date further set forth above.

COCENSYS, INC.                         WARNER-LAMBERT COMPANY


By: /s/ F. Richard Nichol, Ph.D.       By:  /s/ Prof. Ronald M. Cresswell, Ph.D.
    -----------------------------         --------------------------------------
Title:    President and CEO            Title: Vice President and Chairman,
      ---------------------------             Parke-Davis Pharmaceutical 
                                              Research, Warner-Lambert Company
                                              ----------------------------------

                                       3
* Confidential treatment requested