ACP-104, Major Metabolite of Clozapine, Partially Activates Dopamine D2 and
                                 D3 Receptors

    SAN DIEGO, Sept. 22 /PRNewswire-FirstCall/ -- ACADIA Pharmaceuticals Inc.
(Nasdaq: ACAD), a biopharmaceutical company utilizing innovative technology to
fuel drug discovery and clinical development of novel treatments for central
nervous system disorders, today announced publication of research in the
Journal of Pharmacology and Experimental Therapeutics (JPET) that shows that
ACP-104, the major metabolite of clozapine, is a partial agonist that causes
weak activation of dopamine D2 and D3 receptors, whereas clozapine and most
other antipsychotic drugs block these receptors.  ACADIA believes that these
partial agonist properties of ACP-104 may lead to less motoric side effects
than seen with most other antipsychotic drugs.  ACADIA is developing ACP-104
as a novel therapy for schizophrenia, with the added potential benefit of
improving cognition.
    "By combining D2 and D3 dopamine partial agonism, M1 muscarinic agonism,
and 5-HT2A inverse agonism in a single molecule, ACP-104 uniquely addresses
the three most promising target mechanisms for treating psychosis," said Mark
R. Brann, Ph.D., ACADIA's President and Chief Scientific Officer.  "We believe
that ACP-104 represents a new and potential breakthrough approach in
schizophrenia therapy."
    The JPET article (August 31, 2005, e-pub) describes the research conducted
by ACADIA scientists of 41 marketed and experimental antipsychotic drugs and
their ability to alter the activities of dopamine D2, D3, and D4 receptors.
Using ACADIA's proprietary R-SAT(R) technology platform, the scientists
developed assays that detect subtle changes in the activities of these
receptors.  Among the 41 drugs, only two of them, ACP-104 and aripiprazole
(marketed as ABILIFY(R)), were partial agonists causing weak activation of
dopamine D2 and D3 receptors.  Most antipsychotic drugs were shown to block
these dopamine receptors.  Prior research has shown that blockade of the
dopamine receptors may cause undesirable motoric side effects, including
Parkinson-like symptoms and tardive dyskinesia.
    "Precisely balancing dopaminergic tone with an antipsychotic drug being a
partial dopamine agonist is a very exciting concept that I have championed for
many years," said Arvid Carlsson, M.D., Ph.D., Professor Emeritus of
Pharmacology at the University of Goteborg, Sweden, and winner of the 2000
Nobel Prize for Medicine.  "I find it most intriguing that ACP-104, the major
metabolite of the first atypical antipsychotic drug, clozapine, has this
property."

    About ACP-104
    ACP-104 is a small molecule drug candidate that ACADIA has discovered and
is developing as a novel, stand-alone therapy for schizophrenia.  It combines
an atypical antipsychotic efficacy profile with the added potential benefit of
improving cognition, one of the major challenges in treating schizophrenia
today.  ACP-104, or N-desmethylclozapine, is the major metabolite of
clozapine, and has a unique ability to stimulate M1 muscarinic receptors.  The
M1 muscarinic receptors are widely known to play an important role in
cognition.  ACADIA is currently conducting initial Phase II studies to
evaluate safety, tolerability, and preliminary efficacy of ACP-104 in patients
with schizophrenia.

    About Schizophrenia
    Schizophrenia is a debilitating mental illness characterized by
disturbances such as hallucinations and delusions as well as a range of
negative symptoms, including cognitive disturbances and social withdrawal.
Cognitive disturbances often prevent patients with schizophrenia from
readjusting to society and can require patients to be under medical care for
their entire lives.  Despite the availability of current antipsychotic drugs
with worldwide sales of approximately $14 billion, cognitive disturbances are
poorly addressed by existing therapies and represent a large unmet medical
need in the treatment of schizophrenia.

    About ACADIA Pharmaceuticals
    ACADIA Pharmaceuticals is a biopharmaceutical company utilizing innovative
technology to fuel drug discovery and clinical development of novel treatments
for CNS disorders.  ACADIA currently has four drug programs in clinical
development as well as a portfolio of preclinical and discovery assets
directed at large unmet medical needs, including schizophrenia, Parkinson's
disease, neuropathic pain, and glaucoma.  Using its proprietary drug discovery
platform, ACADIA has discovered all of the drug candidates in its product
pipeline.  ACADIA's corporate headquarters is located in San Diego, California
and it maintains research and development operations in both San Diego and
Malmo, Sweden.

    Forward-Looking Statements
    Statements in this press release that are not strictly historical in
nature are forward-looking statements.  These statements include but are not
limited to statements related to the progress and timing of ACADIA's drug
discovery and development programs and related trials, the safety and efficacy
of ACADIA's drug candidates, and the benefits to be derived from ACADIA's
technology and drug candidates, in each case, including ACP-104.  These
statements are only predictions based on current information and expectations
and involve a number of risks and uncertainties.  Actual events or results may
differ materially from those projected in any of such statements due to
various factors, including the risks and uncertainties inherent in drug
discovery, development and commercialization.  For a discussion of these and
other factors, please refer to ACADIA's annual report on Form 10-K for the
year ended December 31, 2004 filed with the United States Securities and
Exchange Commission as well as other subsequent filings with the Securities
and Exchange Commission.  You are cautioned not to place undue reliance on
these forward-looking statements, which speak only as of the date hereof.
This caution is made under the safe harbor provisions of the Private
Securities Litigation Reform Act of 1995.  All forward-looking statements are
qualified in their entirety by this cautionary statement and ACADIA undertakes
no obligation to revise or update this press release to reflect events or
circumstances after the date hereof.

     Contacts:
     ACADIA Pharmaceuticals Inc.
     Lisa Barthelemy, Director, Investor Relations
     (858) 558-2871

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