The following discussion and analysis of our consolidated financial condition and results of operations should be read in conjunction with our unaudited condensed consolidated financial statements and related notes included in this quarterly report on Form 10-Q (this "Quarterly Report") and the audited financial statements and notes thereto as of and for the year ended December 31, 2008 included with our annual report on Form 10-K ("Annual Report") filed with the SEC. Past operating results are not necessarily indicative of results that may occur in future periods.

This Quarterly Report contains forward-looking statements. These forward-looking statements involve a number of risks and uncertainties. Such forward-looking statements include statements about our strategies, objectives, expectations, discoveries, collaborations, clinical trials, product candidates, programs, and other statements that are not historical facts, including statements which may be preceded by the words "intends," "may," "will," "plans," "expects," "anticipates," "projects," "predicts," "estimates," "aims," "believes," "hopes," "potential" or similar words. For such statements, we claim the protection of the Private Securities Litigation Reform Act of 1995. Readers of this Quarterly Report are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date on which they are made. We undertake no obligation to update publicly or revise any forward-looking statements. Actual events or results may differ materially from our expectations. Important factors that could cause actual results to differ materially from those stated or implied by our forward-looking statements include, but are not limited to, the risk factors identified in our filings with the SEC, including this Quarterly Report.

Overview

Background

We are a biopharmaceutical company focused on the development and commercialization of small molecule drugs for the treatment of central nervous system disorders. We currently are developing a portfolio consisting of our five most advanced product candidates including pimavanserin, which is in Phase III development for Parkinson's disease psychosis in collaboration with Biovail Laboratories International SRL ("Biovail"), a subsidiary of Biovail Corporation. In addition to pimavanserin, we have a product candidate in Phase II development for chronic pain and a product candidate in Phase I development for glaucoma, each in collaboration with Allergan, Inc., as well as two programs in IND-track development. All of the product candidates in our pipeline emanate from discoveries made using our proprietary drug discovery platform.

We have incurred substantial operating losses since our inception due in large part to expenditures for our research and development activities. In August 2008, we implemented a strategic restructuring designed to focus resources primarily on our most advanced product candidates, including pimavanserin, and to provide additional financial flexibility and strength. At June 30, 2009, we had an accumulated deficit of $321.8 million. Although we have reduced our operating expenses in connection with the strategic restructuring, we expect our operating losses to continue for at least the next several years as we pursue the clinical development of our product candidates.

We maintain a website at www.acadia-pharm.com to which we regularly post copies of our press releases as well as additional information about us. Our filings with the SEC are available free of charge through our website as soon as reasonably practicable after being electronically filed with or furnished to the SEC. Interested persons can subscribe on our website to email alerts that are sent automatically when we issue press releases, file our reports with the SEC or post certain other information to our website. Information contained in our website does not constitute a part of this Quarterly Report.

Recent Developments

In May 2009, we announced the completion of enrollment in our first pivotal Phase III clinical trial of pimavanserin in patients with Parkinson's disease psychosis. Top-line results from this trial are expected to be announced in the third quarter of 2009.

In May 2009, we entered into a collaboration agreement with Biovail to co-develop and commercialize pimavanserin for neurological and psychiatric indications, including Parkinson's disease psychosis ("PDP") and Alzheimer's disease psychosis ("ADP"), in the United States and Canada. We have retained the rights to pimavanserin in the rest of the world. Under the terms of the agreement, we are entitled to receive aggregate payments, excluding royalties, of up to $395 million. These include an upfront cash payment of $30 million, up to $160 million in potential milestone payments associated with the successful completion of clinical trials, regulatory submissions and approvals of pimavanserin for PDP and ADP, up to $45 million in potential milestones should the parties pursue a third indication, and up to $160 million in potential milestones as certain sales thresholds are met. We also are entitled to receive a 15 percent royalty on annual net sales of pimavanserin up to $100 million and a 20 percent royalty on annual net sales over $100 million. In addition to product royalties, we have the option to co-promote pimavanserin in the United States. Biovail will be responsible for all future costs associated with the development, manufacturing, and commercialization of pimavanserin in all indications with the exception of specified ongoing PDP studies, which we will continue to fund.

In April 2009, we entered into an amendment to extend the research term of our March 2003 collaboration with Allergan. This collaboration originally provided for a three-year research term, which ended in March 2006. The parties previously had extended the research term through March 2009. The most recent amendment extends the research term for one additional year, through March 2010. During the extended research term, the parties will focus joint research efforts on discovery activities in ophthalmic indications.

Revenues

We have not generated any revenues from product sales to date, and we do not expect to generate revenues from product sales for at least the next several years, if at all. Our revenues to date have been generated substantially from payments under our current and past collaboration agreements. As of June 30, 2009, we had received an aggregate of $92.5 million in payments under these agreements, including upfront payments, research funding, and milestone payments. We expect our revenues for the next several years to consist primarily of payments under our current agreements with Biovail, Allergan, and Meiji Seika Kaisha, Ltd. and potential additional collaborations.

In May 2009, we entered into a collaboration agreement with Biovail, pursuant to which we received a $30 million upfront payment. Under the terms of the agreement, we are entitled to receive additional payments of up to an aggregate of $365 million upon successfully achieving development, regulatory and sales milestones. We also are entitled to receive royalties on annual net sales of pimavanserin. Our agreement with Biovail is subject to early termination upon specified events.

We currently are a party to three separate collaboration agreements with Allergan. Pursuant to our March 2003 collaboration agreement with Allergan, we had received an aggregate of $15.9 million in payments as of June 30, 2009, consisting of upfront fees, research funding and related fees. This collaboration originally provided for a three-year research term, which has been extended by the parties through March 2010. We have had a reduced level of research activities and related research funding under this collaboration during the extension. In our two other collaboration agreements with Allergan, the parties are currently pursuing the clinical development of product candidates in the areas of chronic pain and glaucoma. We are eligible to receive payments upon achievement of development and regulatory milestones, as well as royalties on product sales, if any, under each of our three collaboration agreements with Allergan. Each of our agreements with Allergan is subject to early termination upon specified events, including, in the case of one of our agreements, if we have a change in control. Upon the conclusion of the research term under each agreement, Allergan may terminate the agreement by notice.

In March 2009, we entered into a collaboration agreement with Meiji Seika, pursuant to which we received an aggregate of $2 million in license fees in April 2009. Under the agreement, we are eligible to receive up to $25 million in aggregate payments, including the $2 million in license fees already received, in addition to royalties on product sales, if any, in the Asian territory. Meiji Seika also is responsible for the first $15 million of development expenses and we will share the remaining expenses through clinical proof-of-concept, subject to possible adjustment in the event we further license the related product candidate outside of the Asian territory. Our agreement with Meiji Seika is subject to early termination upon specified events.

Research and Development Expenses

Our research and development expenses consist primarily of fees paid to external service providers, salaries and related personnel expenses, facilities and equipment expenses, and supplies and other costs. We charge all research and development expenses to operations as incurred. Our research and development activities are primarily focused on our most advanced product candidates, including pimavanserin.

Prior to our collaboration with Biovail, which we established in May 2009, we were responsible for all costs incurred in the development of pimavanserin as well as the costs associated with our other internal programs. Pursuant to this agreement, Biovail is responsible for all future costs associated with the development of pimavanserin in all indications with the exception of specified ongoing PDP studies, which will continue to be funded by ACADIA. These ongoing studies include our pivotal Phase III trials and related open-label safety extension study. Pursuant to our collaboration with Meiji Seika, which we established in March 2009, Meiji Seika is responsible for the first $15 million of development expenses for the product candidate, AM-831, and the companies will share remaining expenses through clinical proof-of-concept, subject to possible adjustment. Meiji Seika is responsible for all costs associated with the development of AM-831 in the Asian territory after proof-of-concept. We are not responsible for, nor have we incurred, development expenses related to our product candidates, including costs related to clinical trials, in our clinical programs for chronic pain and glaucoma, which we are pursuing in collaboration with Allergan.

We use our internal research and development resources, including our employees and discovery infrastructure, across several projects and many of our costs are not attributable to a specific project but are directed to broadly applicable research activities. Accordingly, we do not report our internal research and development costs on a project basis. We use external service providers to manufacture our product candidates to be used in clinical trials and for the majority of the services performed in connection with the preclinical and clinical development of our product candidates. Our external service costs for pimavanserin increased in the three and six months ended June 30, 2009 compared to the three and six months ended June 30, 2008 primarily due to increased development costs associated with our Phase III program. Our internal research and development expenses decreased significantly in the three and six months ended June 30, 2009 compared to the three and six months ended June 30, 2008 primarily due to our strategic restructuring implemented in August 2008. To the extent that external expenses are not attributable to a specific project, they are included in other external costs. The following table summarizes our research and development expenses for the three and six months ended June 30, 2009 and 2008 (in thousands):

                                          Three Months Ended       Six Months Ended
                                               June 30,                June 30,
                                           2009         2008       2009        2008
                                             (unaudited)             (unaudited)
       External costs:
       Pimavanserin                     $     8,029   $  6,668   $  16,891   $ 12,744
       ACP-1041                                  13      1,253          39      2,633
       ACP-106, AM-831 and other                348      1,000         592      1,374

       Subtotal                               8,390      8,921      17,522     16,751
       Internal costs                         3,306      6,735       6,507     13,661
       Stock-based compensation                 283        380         504        795

       Total research and development   $    11,979   $ 16,036   $  24,533   $ 31,207

1. ACP-104 was a product candidate that we were previously developing. We currently do not anticipate conducting further studies with ACP-104.

At this time, due to the risks inherent in the clinical trial process and given the stage of development of our programs, we are unable to estimate with any certainty the costs we will incur for the continued development of our product candidates for potential commercialization. Due to these same factors, we are unable to determine the anticipated completion dates for our current research and development programs. Clinical development timelines, probability of success, and development costs vary widely. While our current focus is primarily on advancing the clinical development of pimavanserin, we anticipate that we will make determinations as to which programs to pursue and how much funding to direct to each program on an ongoing basis in response to the scientific and clinical success of each product candidate, as well as an ongoing assessment of each product candidate's commercial potential and

our financial position. We cannot forecast with any degree of certainty when and to what extent we will receive cash inflows from the development or commercialization of pimavanserin pursuant to our agreement with Biovail. We also cannot forecast with any degree of certainty which product candidates will be subject to future collaborative or licensing arrangements, when such arrangements will be secured, if at all, and to what degree such arrangements would affect our development plans and capital requirements.

We expect our external research and development expenses to continue to be substantial as we pursue the development of pimavanserin and our other product candidates. The lengthy process of completing clinical trials and seeking regulatory approval for our product candidates requires the expenditure of substantial resources. Any failure by us or delay in completing clinical trials, or in obtaining regulatory approvals could cause our research and development expenses to increase and, in turn, have a material adverse effect on our results of operations.

General and Administrative Expenses

Our general and administrative expenses consist primarily of salaries and other costs for employees serving in executive, finance, business development, and business operations functions, as well as professional fees associated with legal and accounting services, and costs associated with patents and patent applications for our intellectual property.

Critical Accounting Policies and Estimates

Our discussion and analysis of our financial condition and results of operations is based on our consolidated financial statements. We have identified the accounting policies that we believe require application of management's most subjective judgments, often requiring the need to make estimates about the effect of matters that are inherently uncertain and may change in subsequent periods. Our actual results may differ substantially from these estimates under different assumptions or conditions.

Revenue Recognition

We recognize revenues in accordance with Securities and Exchange Commission Staff Accounting Bulletin No. 104, Revenue Recognition, and Emerging Issues Task Force Issue No. 00-21 ("EITF 00-21"), Revenue Arrangements with Multiple Deliverables. Our revenues are primarily related to our collaboration agreements, which may provide for various types of payments to us, including upfront payments, funding of research and development, milestone payments, and licensing fees. Our collaboration agreements also include potential payments for product royalties and commercial co-promotion, however, we have not received revenue from these two sources to date.

We consider a variety of factors in determining the appropriate method of accounting under our collaboration agreements, including whether the various elements can be separated and accounted for individually as separate units of accounting in accordance with EITF 00-21. Where there are multiple deliverables identified within a collaboration agreement that are combined into a single unit of accounting, revenues are deferred and recognized over the expected period of performance. The specific methodology for the recognition of the revenue is determined on a case-by-case basis according to the facts and circumstances applicable to each agreement.

Upfront, non-refundable payments that do not have stand-alone value are recorded as deferred revenue once received and recognized as revenues over the expected period of performance. Revenues from non-refundable license fees are recognized upon receipt of the payment if the license has stand-alone value, we do not have ongoing involvement or obligations, and the fair value of any undelivered items can be determined. Non-refundable payments for research funding are generally recognized as revenues over the period as the related research activities are performed. Payments for reimbursement of external development costs are generally recognized as revenues using a contingency-adjusted performance model over the expected period of performance.

We assess milestone payments on an individual basis and recognize revenues from non-refundable milestone payments when the earnings process is complete and the payment is reasonably assured. Non-refundable milestone payments related to arrangements under which we have continuing performance obligations are recognized as revenue upon achievement of the associated milestone, provided that (i) the milestone event is substantive and its achievability was not reasonably assured at the inception of the agreement and (ii) the amount of the milestone payment is reasonable in relation to the effort expended or the risk associated with the milestone event. Where separate milestone payments do not meet these criteria, we typically recognize revenue using a contingency-adjusted performance model over the remaining period of performance.

Accrued Expenses

We are required to estimate accrued expenses as part of our process of preparing financial statements. Examples of areas in which subjective judgments may be required include costs associated with services provided by contract organizations for preclinical development, manufacturing of clinical materials, and clinical trials. We accrue for costs incurred as the services are being provided by monitoring the status of the trials or services provided, and the invoices received from our external service providers. In the case of clinical trials, a portion of the cost normally relates to the projected cost to treat a patient in our trials and we recognize this cost over the estimated term of the study based on the number of patients enrolled in the trial on an ongoing basis, beginning with patient enrollment. As actual costs become known to us, we adjust our accruals. To date, our estimates have not differed significantly from the actual costs incurred. However, we have expanded the level of our clinical trials and related services. As a result, we anticipate that our estimated accruals for clinical services will be more material to our operations in future periods. Subsequent changes in estimates may result in a material change in our accruals, which could also materially affect our balance sheet and results of operations.

Stock-based Compensation

Effective January 1, 2006, we adopted the fair value recognition provisions of Statement of Financial Accounting Standards ("SFAS, No. 123") (revised 2004), Share-Based Payment ("SFAS No. 123(R)"), to account for employee stock options and stock issued under the employee stock purchase plan.

The value of each employee stock option and each employee stock purchase right granted is estimated on the grant date under the fair value method using the Black-Scholes option pricing model. For options granted prior to January 1, 2006, we amortize the fair value on an accelerated basis. For options granted after January 1, 2006, we amortize the fair value on a straight-line basis. All option expense is amortized over the requisite service period of the awards, which is generally the vesting period. As of June 30, 2009, total unrecognized compensation cost related to stock options and purchase rights was approximately $4.1 million, and the weighted average period over which this cost is expected to be recognized is 2.5 years.

Stock-based awards issued to non-employees other than directors are accounted for using a fair value method and are re-measured to fair value at each period end until the earlier of the date that performance by the non-employee is complete or a performance commitment has been obtained. The fair value of each award is estimated using the Black-Scholes option pricing model.

Results of Operations

Fluctuations in Operating Results

Our results of operations have fluctuated significantly from period to period in the past and are likely to continue to do so in the future. We anticipate that our quarterly and annual results of operations will be impacted for the foreseeable future by several factors, including the timing and amount of payments received pursuant to our current and potential future collaborations, and the progress and timing of expenditures related to our discovery and development efforts. Due to these fluctuations, we believe that the period-to-period comparisons of our operating results are not a good indication of our future performance.

Comparison of the Three Months Ended June 30, 2009 and 2008

Revenues

Revenues totaled $1.8 million for the three months ended June 30, 2009 compared to $177,000 for the three months ended June 30, 2008. The increase in revenues was primarily due to $1.4 million in initial revenues recognized under our collaboration with Biovail, for the period from the effective date of the agreement on May 1, 2009 through June 30, 2009. Revenues from our collaborations with Allergan totaled $265,000 for the three months ended June 30, 2009 compared to $177,000 for the three months ended June 30, 2008. Revenues from our collaboration with Meija Seika and smaller scale research agreements with other parties totaled $147,000 for the three months ended June 30, 2009.

Research and Development Expenses

Research and development expenses decreased to $12.0 million for the three months ended June 30, 2009, including $283,000 in stock-based compensation, compared to $16.0 million for the three months ended June 30, 2008, including $380,000 in stock-based compensation. The decrease in research and development expenses was primarily due to $3.5 million in decreased costs associated with our internal research and development organization and $531,000 in lower external service costs. The decrease in internal research and development costs was primarily attributable to $2.3 million in decreased salaries and related personnel costs, and decreases in laboratory supply, equipment and other costs resulting from our strategic restructuring. External service costs totaled $8.4 million, or 70 percent of our research and development expenses for the three months ended June 30, 2009, compared to $8.9 million, or 56 percent of our research and development expenses, for the comparable period in 2008. Increased development costs for pimavanserin during the three months ended June 30, 2009 were offset by lower costs incurred for ACP-104 and other programs.

General and Administrative Expenses

General and administrative expenses totaled $2.7 million for the three months ended June 30, 2009, including $333,000 in stock-based compensation, compared to $3.2 million for the three months ended June 30, 2008, including $431,000 in stock-based compensation. The decrease in general and administrative expenses was primarily due to $247,000 in decreased salaries and related personnel costs, and decreases in other administrative costs, partially offset by increased external service costs.

Interest Income

Interest income decreased to $117,000 for the three months ended June 30, 2009 from $802,000 for the three months ended June 30, 2008. The decrease in interest income during the three months ended June 30, 2009 was due to decreased yields on our investment security portfolio and lower average levels of cash and investment securities.

Comparison of the Six Months Ended June 30, 2009 and 2008

Revenues

Revenues totaled $2.2 million for the six months ended June 30, 2009 compared to $983,000 for the six months ended June 30, 2008. The increase in revenues was primarily due to $1.4 million in initial revenues recognized under our collaboration with Biovail, which commenced in May 2009, partially offset by lower revenues from our agreements with other parties. Revenues from our collaboration with Meija Seika and smaller scale research agreements with other parties totaled $252,000 for the six months ended June 30, 2009, compared to $388,000 from smaller scale research agreements for the six months ended June 30, 2008. In addition, revenues from our agreement with Sepracor, which ended in January 2008, totaled $91,000 for the six months ended June 30, 2008. Revenues from our agreements with Allergan totaled $534,000 for the six months ended June 30, 2009 compared to $504,000 for the six months ended June 30, 2008.

Research and Development Expenses

Research and development expenses decreased to $24.5 million for the six months ended June 30, 2009, including $504,000 in stock-based compensation, from $31.2 million for the six months ended June 30, 2008, including $795,000 in stock-based compensation. The decrease in research and development expenses was primarily due to $7.4 million in decreased costs associated with our internal research and development organization, partially offset by $771,000 in increased external service costs. The decrease in internal research and development costs was primarily attributable to $4.8 million in decreased salaries and related personnel costs, $1.2 million in decreased laboratory supply costs, and decreases in equipment and other costs resulting from our strategic restructuring. External service costs totaled $17.5 million, or 71 percent of . . .