Arena Pharmaceuticals, Inc.
May 18, 2006

Arena Pharmaceuticals Announces Achievement of Phase 2 Clinical Milestone Under Cardiovascular Disease Collaboration With Merck

SAN DIEGO, May 18, 2006 /PRNewswire-FirstCall via COMTEX News Network/ -- Arena Pharmaceuticals, Inc. (Nasdaq: ARNA) announced today the initiation of a Phase 2 clinical trial of MK-0354, an Arena discovered orally administered drug candidate under development by Merck for the treatment of atherosclerosis and related disorders. The Phase 2 clinical trial triggers a $4 million milestone payment to Arena under the research collaboration and license agreement for compounds targeting a G protein-coupled receptor, or GPCR, that have the potential to regulate plasma lipid profiles, including HDL, or the "good" cholesterol, similar to the therapeutic action of niacin.

The Phase 2 clinical trial is a randomized, double-blind, placebo-controlled study that will further evaluate safety, tolerability and pharmacokinetics, as well as potential efficacy, of MK-0354 in patients with dyslipidemia.

The Phase 1 clinical trial program of MK-0354 included two randomized, double-blind, placebo-controlled studies evaluating the safety, tolerability and pharmacokinetics of MK-0354 in healthy volunteers. In both studies MK-0354 was generally well-tolerated at all doses studied.

"We are pleased with Merck's decision to advance MK-0354," said Jack Lief, President and CEO of Arena. "We look forward to the Phase 2 results and to the continued advancement of this program."

"Merck is pleased with the progress of this program to date," said Kathleen Metters, Ph.D., Senior Vice President, Basic Research, Merck Research Laboratories. "This is another example of Merck's commitment to rapidly develop novel therapies for the treatment of atherosclerosis."

About Atherosclerosis

Atherosclerosis is characterized by the collection of fatty material deposits, such as cholesterol, along artery walls. This fatty material thickens, hardens, and may eventually block the arteries, adversely affecting blood flow and increasing the risk of heart attack and stroke over time. Atherosclerosis accounts for nearly three out of every four deaths from cardiovascular disease. In 1999, U.S. community hospitals billed $26.2 billion for coronary atherosclerosis care. HDL cholesterol, commonly known as the "good" cholesterol, can help clear the fatty deposits from the walls of blood vessels and transport cholesterol to the liver for processing and removal from the body. Drugs that can influence the levels of HDL cholesterol may potentially provide clinical benefits to patients by reducing the risk of heart attack and stroke.

About Arena Pharmaceuticals

Arena is a clinical-stage biopharmaceutical company focusing on the discovery, development and commercialization of small molecule drugs in four major therapeutic areas: metabolic, central nervous system, cardiovascular and inflammatory diseases. Arena is developing a broad pipeline of compounds targeting an important class of drug targets called G protein-coupled receptors, or GPCRs, using its knowledge of GPCRs and its technologies, including CART (Constitutively Activated Receptor Technology) and Melanophore. Arena has four internally discovered, clinical-stage drug candidates for major diseases. The most advanced is lorcaserin hydrochloride, a selective 5-HT2C serotonin receptor agonist that is under investigation for the treatment of obesity and is expected to enter Phase 3 clinical development in the second half of 2006. Arena's lead drug candidate for the treatment of insomnia, APD125, is a compound with a novel mechanism of action (a selective 5-HT2A receptor inverse agonist) with an IND pending before the FDA for the initiation of a Phase 2 trial in patients with chronic insomnia. Arena also has two clinical-stage collaborations with major pharmaceutical companies: Merck & Co., Inc., began a Phase 2 clinical trial of MK-0354, an Arena discovered drug candidate for the treatment of atherosclerosis and related disorders, in the second quarter of 2006; and Ortho-McNeil, Inc., a Johnson & Johnson company, began a Phase 1 clinical trial of APD668, an Arena discovered drug candidate for the treatment of type 2 diabetes, in the first quarter of 2006.

Arena Pharmaceuticals® and Arena® are registered service marks of the company. CART is an unregistered service mark of the company. "APD" is an abbreviation for Arena Pharmaceuticals Development.

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 expected results and continued advancement of MK-0354, the tolerability, side effects and efficacy of MK-0354, the expected clinical trials of lorcaserin hydrochloride and APD125, and other statements about Arena's strategy, technologies, preclinical and internal and partnered clinical 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 FDA may not allow Arena's planned clinical trials to proceed at the time Arena expects or at all, the results of preclinical studies or clinical trials may not be predictive of future results, Arena's ability to partner lorcaserin hydrochloride, APD125 or other of its compounds or programs, the timing, success and cost of Arena's research, out-licensing endeavors and clinical trials, Arena's ability to obtain additional financing, Arena's ability to obtain and defend its patents, and the timing and receipt of payments and fees, if any, from Arena's collaborators. 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.

SOURCE Arena Pharmaceuticals, Inc.

Jack Lief, President and CEO, or David Walsey, Director, Corporate Communications, +1-858-453-7200, ext. 1315, both of Arena Pharmaceuticals; or Media Relations, Carolyn Wang of WeissComm Partners, +1-415-946-1065, for Arena Pharmaceuticals, Inc.