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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 or TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 ARENA PHARMACEUTICALS , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 136 Heber Avenue , Suite 204 , Park City , UT ( Address of principal executive offices ) For the transition period from to COMMISSION FILE NUMBER 000-31161 Title of each class Common Stock , par value $ 0.0001 per share Securities registered pursuant to 12 ( b ) of the Act : Trading Symbol ( s ) . ARNA Securities registered pursuant to 12 ( g ) of the Act : None No Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes > Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No 858.453.7200 ( Registrant's telephone number , including area code ) | □ 23-2908305 ( I.R.S. Employer Identification No. ) 84060 ( Zip Code ) X Name of each exchange on which registered The Nasdaq Global Select Market Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes X No No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , ” “ smaller reporting company ” and “ emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer Non - accelerated filer Accelerated filer Smaller reporting company Emerging growth company 000 If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . □ Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No X The aggregate market value of the voting and non - voting common equity held by non - affiliates of the registrant was approximately $ 3.6 billion as of June 30 , 2020 , based on the last sale price of the registrant's common stock as reported on the Nasdaq Global Select Market on such date . For purposes of this calculation , shares of the registrant's common stock held by directors and executive officers have been excluded . This number is provided only for purposes of this Annual Report on Form 10 - K and does not represent an admission that any particular person or entity is an affiliate of the registrant . As of February 18 , 2021 , there were 60,334,648 shares of the registrant's common stock outstanding . DOCUMENTS INCORPORATED BY REFERENCE Certain information required by Part III of this Annual Report on Form 10 - K is incorporated by reference from the Registrant's Definitive Proxy Statement for the Annual Meeting of Stockholders to be held in June 2021 , which will be filed with the Securities and Exchange Commission on or before April 30 , 2021 .