Arena Pharmaceuticals (ARNA) 10-K 2005 FY Annual report

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statements on Form S-3 (Nos. 333-122435, 333-115670,
333-112542, 333-129519 and 333-131310) and Form S-8 (Nos. 333-45330, 333-45332, 333-62894 and 333-86350) of Arena Pharmaceuticals, Inc. and in the related Prospectuses of our reports dated February 13, 2006, with respect the consolidated financial statements of Arena Pharmaceuticals, Inc.,  Arena Pharmaceuticals, Inc. management’s assessment of the effectiveness of internal control over financial reporting, and the effectiveness of internal control over financial reporting of Arena Pharmaceuticals, Inc. included in the Annual Report (Form 10-K) for the year ended December 31, 2005.

	/s/ ERNST & YOUNG LLP
San Diego, California
March 2, 2006