Studies have indicated that individuals who have used MDMA may have decreased performance in memory tests compared to nonusers. These studies are presently controversial because they involved people who used a variety of other drugs. Furthermore, it is difficult to rule out possible pre-existing differences between research subjects and controls.

Source

E. Gouzoulis-Mayfrank; J. Daumann; F. Tuchtenhagen; S. Pelz; S. Becker; H.J. Kunert; B. Fimm; H. Sass; Impaired cognitive performance in drug free users of recreational ecstasy (MDMA), Journal Neurol Neurosurg Psychiatry Vol 68, June 2000, 719-725; K.I. Bolla; U.D.; McCann; G.A. Ricaurte; Memory impairment in abstinent MDMA ('Ecstasy') users, Neurology Vol 51, Dec 1998, 1532-1537.