X0306 4 2021-01-27 0 0001419600 Flexion Therapeutics Inc FLXN 0001806204 Layman Melissa C/O FLEXION THERAPEUTICS, INC. 10 MALL ROAD, SUITE 301 BURLINGTON MA 01803 0 1 0 0 Chief Commercial Officer Common Stock 2021-01-27 4 A 0 30000 0.00 A 91000 D Common Stock 2021-01-28 4 S 0 2624 12.55 D 88376 D On April 1, 2020, the Reporting Person was granted 30,000 restricted stock units. The vesting of the shares under the restricted stock unit award was to be based on the achievement of a specified amount of 2020 revenues from ZILRETTA product sales established at the time of the Compensation Committee's approval of the restricted stock unit award. On January 27, 2021, the Compensation Committee certified the achievement of a specified amount of 2020 revenues from ZILRETTA product sales resulting in the commencement of vesting of 30,000 shares. The Reporting Person previously reported the restricted stock units in Table II of Form 4. Sale of shares to cover income tax withholding obligations associated with the vesting of a restricted stock unit award granted to the Reporting Person on April 1, 2020. /s/ Mark S. Levine, Attorney-in-Fact 2021-01-29