Arena Pharmaceuticals Offering 14,414,370 Shares Of Common Stock

As disclosed previously in our Current Report on Form 8-K filed on November 8, 2011, we entered into a Common Stock Purchase Agreement, or Purchase Agreement, with Azimuth Opportunity, L.P., or Azimuth, pursuant to which we may, from time to time and subject to the terms and limitations set forth in the Purchase Agreement, sell Azimuth shares of our common stock. On March 9, 2012, we expect to settle with Azimuth on the purchase of 14,414,370 shares of our common stock under the Purchase Agreement at an aggregate purchase price of $25.0 million. We will receive estimated net proceeds from the sale of these shares of approximately $24.7 million after deducting our estimated offering expenses. In connection with this sale of our common stock, we are filing, as Exhibit 5.1 hereto, an opinion of our counsel, Cooley LLP. The foregoing description is qualified in its entirety by reference to the Purchase Agreement, which was filed as an exhibit to our Current Report on Form 8-K filed on November 8, 2011, and is incorporated herein by reference.