The following discussion and analysis of our consolidated financial condition and results of operations should be read in conjunction with our consolidated financial statements and related notes included elsewhere in this report. Past operating results are not necessarily indicative of results that may occur in future periods. This discussion contains forward-looking statements, which involve a number of risks and uncertainties. Such forward-looking statements include statements about our strategies, objectives, expectations, discoveries, collaborations, clinical trials, proprietary and external programs, and other statements that are not historical facts, including statements which may be preceded by the words "believes," "expects," "hopes," "may," "will," "plans," "intends," "estimates," "could," "should," "would," "continue," "seeks," "aims," "projects," "predicts," "pro forma," "anticipates," "potential" or similar words. For forward-looking statements, we claim the protection of the Private Securities Litigation Reform Act of 1995. Readers of this 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 or revise publicly any forward-looking statements. Forward-looking statements are not guarantees of performance. Actual results or events may differ materially from those anticipated in our forward-looking statements as a result of various factors, including those set forth under the section captioned "Risk Factors" elsewhere in this report. Information in the following discussion for a yearly period means for the year ended December 31 of the indicated year.

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 four most advanced product candidates including pimavanserin, which is in Phase III development for the treatment of Parkinson's disease psychosis. We also have reported positive results with pimavanserin in a Phase II trial as a co-therapy in schizophrenia and in a proof-of-concept clinical study for sleep maintenance insomnia. We have retained worldwide commercialization rights to pimavanserin. In addition, we have a product candidate in Phase II for chronic pain and a product candidate in Phase I for glaucoma, each in collaboration with Allergan, Inc., and ACP-106 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. In connection with the restructuring, we reduced our total workforce by about 50 percent and have reduced our internal operating expenses significantly. At December 31, 2008, we had an accumulated deficit of $294.1 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.

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 research and milestone payments under our collaboration agreements. We have established three separate collaboration agreements with Allergan. We also entered into agreements with Sepracor and The Stanley Medical Research Institute, or SMRI, the terms of which ended in January 2008 and May 2007, respectively, as well as smaller scale research and license agreements with other parties. As of December 31, 2008, we had received an aggregate of $59.5 million in payments under these agreements, including research funding and related fees and upfront and milestone payments. We expect our revenues for the next several years to consist primarily of payments under our current agreements with Allergan and any additional collaborations, including any upfront payments upon execution of new agreements, research funding throughout the research term of our agreements with these parties, and milestone payments contingent upon achievement of agreed-upon objectives.

Pursuant to our March 2003 collaboration agreement with Allergan, we had received an aggregate of $15.4 million in payments as of December 31, 2008, 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 2009. We have had a reduced level of research activities and related research funding under this collaboration during the extension. We are also a party to two other collaboration agreements with Allergan, under which we are currently pursuing the clinical development of product candidates in the areas of chronic pain and glaucoma. We are eligible to receive milestone payments and 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 by the collaborator upon specified events, including if we breach the agreement or, 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.

Pursuant to a three-year collaboration agreement with Sepracor, the term of which ended in January 2008, we received $6.7 million in research funding. In connection with this agreement, Sepracor also purchased an aggregate of $20 million of our common stock. Pursuant to a development agreement with SMRI, the term of which ended in May 2007, we received an aggregate of $5.0 million in funding to support the development of a product candidate. Each of the Sepracor and SMRI agreements has ended and will provide no future funding to us.

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. We are responsible for all costs incurred in the development of pimavanserin as well as the costs associated with our other internal programs. We are not responsible for, nor have we incurred, development expenses, 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 significantly in 2008 relative to previous years primarily due to increased clinical development costs associated

with our Phase III program. 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 years ended December 31, 2008, 2007 and 2006 (in thousands):

                                                   Years Ended December 31,
                                                  2008        2007       2006
         Costs of external service providers:
         Pimavanserin                           $  27,189   $ 10,932   $ 18,930
         ACP-1041                                   2,658     16,480      3,722
         ACP-106 and other                          2,251      1,604      1,529

         Subtotal                                  32,098     29,016     24,181
         Internal costs                            23,327     26,205     23,351
         Stock-based compensation                   1,325      2,721      1,866

         Total research and development         $  56,750   $ 57,942   $ 49,398

1. ACP-104 was a product candidate that we were developing as a treatment for patients with schizophrenia. 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 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. As a result, we cannot be certain when and to what extent we will receive cash inflows from the commercialization of our product candidates.

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. While our significant accounting policies are described in more detail in the notes to consolidated financial statements included in this report, we believe that the following accounting policies require the application of significant judgments and estimates.

Revenue Recognition

We recognize revenues in accordance with Securities and Exchange Commission Staff Accounting Bulletin No. 104, Revenue Recognition. Arrangements with multiple elements are accounted for in accordance with Emerging Issues Task Force Issue No. 00-21, or EITF 00-21, Revenue Arrangements With Multiple Deliverables. We analyze our multiple element arrangements to determine whether the elements can be separated and accounted for individually as separate units of accounting in accordance with EITF 00-21. Our revenues are primarily related to our collaboration agreements, and such agreements may provide for various types of payments to us, including upfront payments, research funding and related fees during the term of the agreement, milestone payments based on the achievement of established development objectives, licensing fees, and royalties on future product sales.

Upfront, non-refundable payments under collaboration agreements are recorded as deferred revenue once received and recognized ratably over the term of the agreement. Non-refundable payments for research funding are generally recognized as revenues over the period as the related research activities are performed. Revenues from non-refundable milestones are recognized 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 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 triggering event. 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.

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, or SFAS, No. 123 (revised 2004), Share-Based Payment, or 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 December 31, 2008, total unrecognized compensation cost related to stock options and purchase rights was approximately $5.7 million, and the weighted average period over which this cost is expected to be recognized is 2.7 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 Years Ended December 31, 2008 and 2007

Revenues

Revenues totaled $1.6 million in 2008 compared to $7.6 million in 2007. The decrease in revenues was primarily due to the completion of our agreements with Sepracor and SMRI, as well as lower revenues from our collaborations with Allergan and smaller scale research and license agreements with other parties. Revenues from our agreement with Sepracor totaled $91,000 in 2008 compared to $3.4 million in 2007. Revenues from our agreement with SMRI, which ended in May 2007, totaled $1.0 million in 2007. Revenues from our collaborations with Allergan totaled $1.0 million in 2008 compared to $1.6 million in 2007. Revenues from other research and license agreements totaled $487,000 in 2008 compared to $1.6 million in 2007.

Research and Development Expenses

Research and development expenses totaled $56.8 million in 2008, including $1.3 million in stock-based compensation, compared to $57.9 million in 2007, including $2.7 million in stock-based compensation. The decrease in research and development expenses was primarily due to $2.9 million in decreased costs associated with our internal research and development organization and lower stock-based compensation, offset by $3.1 million in increased external service costs. The decrease in internal research and development costs was primarily attributable to $1.2 million in decreased salaries and related personnel costs, $1.1 million in decreased laboratory supply costs, and decreases in equipment and other costs. The decrease in salaries and related personnel costs was net of a $1.7 million charge recorded during the third quarter of 2008 in connection with workforce reductions from our strategic restructuring. External service costs totaled $32.1 million, or 57 percent of our research and development expenses in 2008, compared to $29.0 million, or 50 percent of our research and development expenses in 2007. The increase in external expenses was largely attributable to increased clinical development costs for pimavanserin offset, in part, by reduced costs for ACP-104.

General and Administrative Expenses

General and administrative expenses totaled $11.8 million in 2008, including $1.7 million in stock-based compensation, compared to $12.3 million in 2007, including $1.6 million in stock-based compensation. The decrease in general and administrative expenses was primarily due to decreased professional fees and other administrative costs, partially offset by increased salaries and related personnel costs. The increases in salaries and related personnel costs were primarily attributable to a charge of $454,000 recorded during the third quarter of 2008 in connection with workforce reductions from our strategic restructuring.

Interest Income

Interest income decreased to $2.9 million in 2008 from $6.5 million in 2007. The decrease in interest income was due to lower average levels of cash and investment securities and decreased yields on our investment security portfolio during 2008.

Comparison of the Years Ended December 31, 2007 and 2006

Revenues

Revenues totaled $7.6 million in 2007 compared to $8.1 million in 2006, and were comprised of revenues from our collaborations with Sepracor and Allergan as well as our agreements with SMRI and other parties. The decrease in revenues was primarily due to lower research funding from our collaborations with Allergan and Sepracor, and completion of our agreement with SMRI, partially offset by increased revenues from smaller scale research and license agreements with other parties. Revenues from our collaborations with Allergan totaled $1.6 million in 2007 compared to $2.2 million in 2006. Revenues from our collaboration with Sepracor totaled $3.4 million in 2007 compared to $3.8 million in 2006. Revenues from our agreement with SMRI, which ended in May 2007, totaled $1.0 million in 2007 compared to $2.0 million in 2006.

Research and Development Expenses

Research and development expenses totaled $57.9 million in 2007, including $2.7 million in stock-based compensation, compared to $49.4 million in 2006, including $1.9 million in stock-based compensation, primarily due to increased clinical development activity associated with our proprietary clinical programs. The increase in research and development expenses was primarily due to $4.8 million in increased fees paid to external service providers, $3.3 million in increased salaries and related personnel costs, and $855,000 in increased stock-based compensation, partially offset by a net reduction in other expenses. External service costs totaled $29.0 million, or 50 percent of our research and development expenses in 2007, compared to $24.2 million, or 49 percent of our research and development expenses in 2006.

General and Administrative Expenses

General and administrative expenses totaled $12.3 million in 2007, including $1.6 million in stock-based compensation, compared to $11.3 million in 2006, including $1.5 million in stock-based compensation. The increase in general and administrative expenses was primarily due to $552,000 in increased salaries and related personnel costs and increases in other administrative costs, offset in part by decreases in professional fees associated with accounting and legal services.

Gain From Settlement of Litigation

In 2006, we recorded a gain of $3.6 million associated with an agreement we entered into to fully settle a civil action inclusive of all fees and costs.

Interest Income

Interest income increased to $6.5 million in 2007 from $4.2 million in 2006. The increase in interest income was primarily due to higher average levels of cash and investment securities resulting from sales of our common stock.

Liquidity and Capital Resources

Since inception, we have funded our operations primarily through sales of our equity securities, payments received under our collaboration agreements, debt financings, and interest income. As of December 31, 2008, we had received $324.8 million in net proceeds from sales of our equity securities, including $6.9 million in debt we had retired through the issuance of our common stock, $59.5 million in payments from collaboration agreements, $22.4 million in debt financing, and $21.6 million in interest income.

At December 31, 2008, we had approximately $60.1 million in cash, cash equivalents and investment securities compared to $126.9 million at December 31, 2007. We have invested a substantial portion of our available cash in a money market fund wholly-backed by U.S. Treasury collateral and in investment securities consisting of high quality, marketable debt instruments of corporations, financial institutions, and government sponsored enterprises. We have adopted an investment policy and established guidelines relating to credit quality, diversification and maturities of our investments to preserve principal and maintain liquidity. All investment securities have a credit rating of at least AA or A1+/P1 as determined by Moody's Investors Service and/or Standard & Poor's. We do not have any direct investments in auction-rate securities or securities that are collateralized by assets that include mortgages or subprime debt. Our investment portfolio has not been adversely impacted by the disruption in the credit markets. However, if there is continued and expanded disruption in the credit markets, there can be no assurance that our investment portfolio will not be adversely affected in the future.

We have consumed substantial amounts of capital since our inception. In August 2008, we implemented a strategic restructuring designed to focus resources on our most advanced product candidates and provide additional financial flexibility and strength. In connection with the restructuring, we reduced our total workforce by about 50 percent. Our internal operating expenses, including personnel and related costs, were reduced significantly following the restructuring and we anticipate that the cash used in our operating activities during 2009 will be below its 2008 level.

We believe that our existing cash resources and the anticipated payments from our collaborations will be sufficient to fund our cash requirements into the first half of 2010. In August 2008, we entered into a Committed Equity Financing Facility, or CEFF, designed to provide us with added financial strength and flexibility. The CEFF provides us with access, at our discretion, to up to $60 million of capital during a three-year period through the sale of newly-issued shares of our common stock. We may access capital under the CEFF in tranches of up to a maximum of between 2.0 and 3.5 percent of our market capitalization at the time of the draw down of each tranche, subject to certain conditions, including a minimum share price threshold of $1.50. The funds that can be raised under the CEFF, if available, will depend on the then-current price of our common stock and the number of shares actually sold, which may not exceed an aggregate of approximately 7 million shares. The shares would be sold at discounts ranging from 6 percent to 12 percent, depending on the average market price of our common stock during the applicable pricing period.

We will require significant additional financing in the future to fund our operations. Our future capital requirements will depend on, and could increase significantly as a result of, many factors, including:

. . .