Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statements on Form S-3 (No. 333-219099) and Form S-8 (Nos. 333-193907, 333-202957, 333-210111, 333-216615, 333-221373 and 333-223532) of Flexion Therapeutics, Inc. of our report dated February 28, 2019 relating to the financial statements and the effectiveness of internal control over financial reporting, which appears in this Form 10-K.