AMENDMENT NO. 1 TO ARENA PHARMACEUTICALS, INC. AMENDED AND RESTATED SEVERANCE BENEFIT PLAN

Exhibit 10.1

AMENDMENT NO. 1 TO

ARENA PHARMACEUTICALS, INC.

AMENDED AND RESTATED SEVERANCE BENEFIT PLAN

The Arena Pharmaceuticals, Inc., Amended and Restated Severance Benefit Plan, originally effective on January 20, 2006, and amended and restated on December 30, 2008 (as amended, the “Plan ”), is hereby further amended as of February 10, 2012, by this Amendment No. 1 as follows:

Exhibit A of the Plan is deleted and replaced with Exhibit A to this Amendment No. 1.

To record the adoption of this Amendment No. 1, Arena Pharmaceuticals, Inc., has caused its duly authorized officer to execute the same this 13th day of February 2012.

EXHIBIT A