SAN DIEGO, CA, and WOODCLIFF LAKE, NJ, September [26], 2011 - Arena Pharmaceuticals, Inc. (NASDAQ: ARNA) and Eisai Inc. announced today that new data analyses from the lorcaserin Phase 3 clinical trial program will be presented in poster sessions at Obesity 2011, the 29th Annual Scientific Meeting of The Obesity Society in Orlando, Florida. The posters highlighted below will be displayed in the Cypress Ballroom of the Orlando World Center Marriott on October 3, 2011, from 9:30 a.m. to 1:45 p.m. Eastern Time (ET) and from 3:15 p.m. to 6:30 p.m. ET. Authors will be available at the posters on October 3, 2011, from 12:30 p.m. to 1:30 p.m. ET.

- Effects of Lorcaserin, a Selective Serotonin 2C Agonist, on Cardiac Valvular Regurgitation in Obese and Overweight Patients During Exposures up to Two Years
Author: Neil J. Weissman, M.D., President of MedStar Health Research Institute and Professor of Medicine, Georgetown University
Poster number: 601-P

- Lorcaserin Reduced Weight and Improved Glycemic Control Across Patient Subgroups in Patients with Type 2 Diabetes
Author: Brian L. Raether, Arena's Senior Clinical Project Manager, Clinical Operations
Poster number: 603-P

- Safety and Efficacy of Lorcaserin: Comparison of Diabetic and Non-Diabetic Patient Populations
Author: Scott C. Stubbe, Arena's Associate Director, Clinical Operations
Poster number: 604-P

About Lorcaserin

Lorcaserin is an investigational drug candidate intended for weight management, including weight loss and maintenance of weight loss, in patients who are obese (BMI ≥30) or patients who are overweight (BMI ≥27) and have at least one weight-related co-morbid condition. Lorcaserin is a new chemical entity that is believed to act as a selective serotonin 2C receptor agonist. The serotonin 2C receptor is expressed in the brain, including the hypothalamus, an area believed to be involved in the control of appetite and metabolism. Arena has patents that cover lorcaserin in the United States and other jurisdictions that in most cases are capable of continuing into 2023 without taking into account any patent term extensions or other exclusivity Arena might obtain.

Arena submitted a New Drug Application (NDA) for lorcaserin to the FDA in December 2009, and the FDA issued a Complete Response Letter (CRL) in October 2010. Arena's wholly owned subsidiary, Arena Pharmaceuticals GmbH, has granted Eisai Inc. exclusive rights to market and distribute lorcaserin in the United States subject to FDA approval of the lorcaserin NDA.

Lorcaserin Phase 3 Clinical Trial Program Overview

The lorcaserin Phase 3 clinical trial program consists of three double-blind, randomized, placebo-controlled trials - BLOOM (Behavioral modification and Lorcaserin for Overweight and Obesity Management), BLOSSOM (Behavioral modification and LOrcaserin Second Study for Obesity Management) and BLOOM-DM (Behavioral modification and Lorcaserin for Overweight and Obesity Management in Diabetes Mellitus) - that together enrolled approximately 7,800 patients. BLOOM and BLOSSOM evaluated lorcaserin versus placebo in obese patients or overweight patients with at least one weight-related co-morbid condition. BLOOM evaluated 3,182 patients over a two-year treatment period, and BLOSSOM evaluated 4,008 patients over a one-year treatment period. BLOOM-DM evaluated 604 obese and overweight patients with type 2 diabetes over a one-year treatment period. The trials included a standardized program of moderate diet and exercise guidance.

About Arena Pharmaceuticals

Arena is a clinical-stage biopharmaceutical company focused on discovering, developing and commercializing oral drugs that target G protein-coupled receptors, an important class of validated drug targets, in four major therapeutic areas: cardiovascular, central nervous system, inflammatory and metabolic diseases.

Arena Pharmaceuticals^® and Arena^® are registered service marks of the company.

About Eisai Inc.

Eisai Inc. was established in 1995 and is ranked among the top-25 US pharmaceutical companies (based on retail sales). The company began marketing its first product in the United States in 1997 and has rapidly grown to become a fully integrated pharmaceutical business. Eisai's areas of commercial focus include neurology, gastrointestinal disorders and oncology/critical care. The company serves as the US pharmaceutical operation of Eisai Co., Ltd., a research-based human health care (hhc) company that discovers, develops and markets products throughout the world.

Eisai has a global product creation organization that includes US-based R&D facilities in Massachusetts, New Jersey, North Carolina and Pennsylvania as well as manufacturing facilities in Maryland and North Carolina. The company's areas of R&D focus include neuroscience; oncology; vascular, inflammatory and immunological reaction; and antibody-based programs. For more information about Eisai, please visit www.eisai.com/us.

Forward-Looking Statements

Certain statements in this press release are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include statements about the advancement, therapeutic indication and use, safety, efficacy, tolerability, mechanism of action and potential of lorcaserin; the response to the CRL for the lorcaserin NDA, potential approval of lorcaserin and related plans and activities; the Eisai collaboration and potential activities thereunder; lorcaserin's patent coverage; and Arena's focus, goals, strategy, research and development programs, and ability to develop compounds and commercialize drugs. For such statements, Arena claims the protection of the Private Securities Litigation Reform Act of 1995. Actual events or results may differ materially from Arena's expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, but are not limited to, the following: the timing of regulatory review and approval is uncertain; the risk that data and other information related to Arena's research and development programs may not meet safety or efficacy requirements or otherwise be sufficient for regulatory approval; Arena's response to the CRL for the lorcaserin NDA or submission of a Marketing Authorization Application for regulatory approval of lorcaserin may not be submitted when anticipated, if at all; the FDA may request other information prior to or after Arena submits such response or approval of the lorcaserin NDA; unexpected or unfavorable new data; risks related to commercializing new products; Arena's ability to obtain and defend its patents; the timing, success and cost of Arena's research and development programs; results of clinical trials and other studies are subject to different interpretations and may not be predictive of future results; clinical trials and other studies may not proceed at the time or in the manner expected or at all; Arena's ability to obtain adequate funds; risks related to relying on collaborative agreements; the timing and receipt of payments and fees, if any, from collaborators; and satisfactory resolution of pending and any future litigation or other disagreements with others. Additional factors that could cause actual results to differ materially from those stated or implied by Arena's forward-looking statements are disclosed in Arena's filings with the Securities and Exchange Commission. These forward-looking statements represent Arena's judgment as of the time of this release. Arena disclaims any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.