<PAGE>

                                                                    Exhibit 10.2

               AMENDMENT TO THE EXCLUSIVE PATENT LICENSE AGREEMENT
               BETWEEN IRISYS RESEARCH & DEVELOPMENT, LLC AND THE
                 CENTER FOR NEUROLOGIC STUDY DATED APRIL 2, 1997

      This Amendment, dated April 11, 2000, is entered into by IriSys Research &
Development, LLC (Licensee), and the Center for Neurologic Study (Licensor).

                                    RECITALS

      WHEREAS, IriSys Research & Development, LLC (IriSys) and the Center for
Neurologic Study (CNS) entered into an Exclusive Patent License Agreement, dated
April 2, 1997, whereby Licensor granted IriSys the exclusive license and rights
to the "LICENSED PATENTS" as defined in that agreement and;

      WHEREAS, IriSys desires to sublicense its exclusive license and rights to
the "Licensed Patents" to a third-party entity and;

      WHEREAS, such third-party entity will desire a worldwide sublicense to the
"Licensed Patents" before committing substantial financial resources to develop
and commercialize the "Licensed Patents" and;

      WHEREAS, the underlying Exclusive Patent License Agreement between IriSys
and Licensor contains certain provisions which require amendment to provide a
prospective third-party entity with sufficient confidence to commit the
financial resources necessary to develop and commercialize the "Licensed
Patents".

      NOW, THEREFORE, IriSys and Licensor, hereby amend the Exclusive Patent
License Agreement dated April 2, 1997 pursuant to Paragraph 13.8 of that
Agreement as follows:

      1.    Paragraph 2.1 shall substitute "World" for the United States.

      2.    Paragraph 2.2 shall eliminate the word "partial" from the term
"partial consideration" and eliminate from (b) "that have not expired at the
time of the receipt of such Net Revenues."

      3.    Paragraph 4 shall add the following: Notwithstanding the above,
Licensor agrees that IriSys may share any proprietary information relating to
this Agreement or the Licensed Patents with any prospective third-party licensee
of the "Licensed Patents" providing such third party agrees in writing to be
bound by the disclosure restrictions of this paragraph. The disclosure
restrictions of this paragraph shall not apply to proprietary

<PAGE>

information which is reasonably required to obtain funding or governmental
approval for the development and commercialization of the "Licensed Patents."

      4.    Paragraph 5 will be revised to replace the first three sentences as
follows: Licensee or its sublicensees retains the sole right and discretion to
file and prosecute any foreign or US patent applications and maintain patents
relating to the Licensed Patents or any improvements made by Licensor. Licensee
or its sublicensees will provide any status reports or other information
relating to patents or patent applications that Licensor requests in writing.
Unless agreed otherwise in writing, in advance, Licensor will not file, apply
for or prosecute any foreign patents corresponding to the Licensed Patents.
Furthermore, Licensor agrees that any improvements to the technology expressly
claimed by the Licensed Patents shall be included in the exclusive license
granted to IriSys under this Agreement although ownership of such improvements
shall remain with the Licensor.

      5.    Paragraph 6.1 shall add the following: In the event there is a
dispute regarding the amount of payment due, such dispute shall be resolved in
accordance with Paragraph 13.9 and the exclusive license granted by this
Agreement shall not be terminated pending resolution of the dispute. The
foregoing sentence shall apply, however, only provided IriSys has actually been
paid by its sublicensee or has otherwise received the sums in dispute; and only
provided the dispute is between IriSys and Licensor. In addition, if IriSys has
actually been paid by its sublicensee or has otherwise received the sums in
dispute, IriSys shall forthwith place the disputed sums in escrow, at a place
acceptable to Licensor, pending resolution of the dispute.

      6.    Paragraph 6.3 shall eliminate the following sentence: "In the event
of any expiration or termination of this Agreement, the rights and licenses
granted Licensee under this Agreement will terminate but all other provisions of
this Agreement will continue in accordance with their terms."

      In lieu of the above sentence the following provision is hereby added: In
the event there is a dispute regarding any breach of this Agreement, material or
otherwise, including but not limited to expiration or termination disputes, such
dispute shall be resolved in accordance with Paragraph 13.9 of this Agreement
and the exclusive license and rights granted Licensee under this Agreement shall
continue in full force and effect pending final resolution of such dispute.

      7.    Paragraph 6.4 shall read: Notwithstanding any other provision of
this Agreement, Licensee shall be considered to have committed an event of
default, and Licensor shall have the right to declare that this Agreement and
the license granted hereunder are terminated (which declaration of termination
shall not be effective until there is a resolution of any disputes on the
subject of termination pursuant to arbitration in accordance with Paragraph
13.9).

                                       2
<PAGE>

      8.    Paragraph 6.4.1 shall read: Licensee warrants, represents, and
covenants that it will undertake all reasonable efforts to obtain from its
Sublicensee a development plan that requires the Sublicensee's commercially
reasonable efforts to expeditiously develop and commercialize the Licensed
Products. Further, Licensee will use commercially reasonable efforts to monitor
the implementation and progress of the development plan to attempt to obtain
maximum commercial advantage and timely payment of any sums due Licensor.
Licensee will, from time to time and as appropriate, provide the Licensor with
updates on both the Sublicensee's development plan and the progress made against
that plan.

      9.    Paragraph 6.4.2 is hereby eliminated in its entirety.

      10.    Paragraph 6.5 will be added as follows: Survival of Sublicenses. In
the event of termination of this Agreement, no subsisting sublicense granted
therefore by Licensee pursuant to this Agreement will thereupon terminate,
unless such effect is desired by the sublicensee, but will instead become a
direct license as between Licensor and the party sublicensed. Licensee will
include this survival provision in substantial form and legal effect, in any
sublicense agreement between itself and any sublicensee.

      11.    Paragraph 8 shall add the following: Notwithstanding the above,
Licensor agrees that IriSys may sublicense the "Licensed Patents" and any
incidental rights thereto, to a third-party sublicensee by giving ten (10) days
prior written notice before signing the sublicense agreement. In the event there
is a material dispute arising out of this Agreement such sublicensee shall have
standing as a real party in interest to participate in any arbitration commenced
under Paragraph 13.9 of this Agreement. Any party initiating arbitration under
this Agreement shall give the same notice to the sublicensee as required of a
third party to this Agreement. Notwithstanding the foregoing, before the
sublicensee is permitted to participate in any arbitration, the sublicensee
shall agree in writing to be bound by the terms of Paragraph 13.9 of this
Agreement; and also to be bound by the arbitrators' decision in all respects.

      12.    Paragraph 13.1 shall insert the phrase: "as amended herein" between
the words "Agreement" and "Licensee."

      13.    13.3 shall be revised as follows: Licensee shall indemnify and hold
harmless Licensor and their employees and officers and their respective
successors, heirs and assigns, from any action, claim or liability, including,
without limitation, liability for death, personal injury, or property damages
arising directly or indirectly from Licensee's possession, distribution or other
use of Licensed Products under this Agreement and/or from Licensee's publication
or distribution of test reports, data and other information relating to Licensed
Products.

      14.    Paragraph 14 entitled Additional Amended Provisions shall be added
to the Agreement as follows:

                                       3
<PAGE>

            14.1  As of the Effective Date of this Amendment, the parties agree
that there is no dispute between them pertaining to the "Licensed Patents".

            14.2  Schedule A of the Agreement shall be expanded to include all
Licensor patents, foreign or United States, which directly relate to the subject
matter contained in each of the five (5) Licensed Patents including, without
limitation, United States Patent 5,863,927 issued January 26, 1999 entitled,
"Dextromethorphan and an Oxidase Inhibitor for Treating Intractable Conditions"
and United States Patent Application Number 09/471,060, filed December 22, 1999,
entitled, "Dextromethorphan and Oxidase Inhibitor for Weaning Patients from
Narcotics and Anti-Depressants."

            14.3  All provisions of the Patent License Agreement between the
parties dated April 2, 1997 not in conflict with this Amendment shall remain in
full force and effect.

            14.4  Should any conflict arise regarding the interpretation of any
provision of the April 2, 1997 Agreement and any provision of this Agreement,
this Amendment provision shall supersede the Agreement provision.

      The parties herein, by subscribing to this Amendment hereby signify their
consent to this Amendment.

                                             IRISYS RESEARCH & DEVELOPMENT, LLC
                                             (LICENSEE)

                                             By: Gina M. Stack
                                                 _______________________________

                                             Date: April 11, 2000
                                                  ______________________________

                                             THE CENTER FOR NEUROLOGIC STUDY
                                             (LICENSOR)

                                             By: Richard A. Smith
                                                ________________________________

                                             Date: April 11, 2000
                                                  ______________________________

                                       4