There have been over 100 scientific studies examining the effects and side-effects of Ecstasy. Fifteen in particular have studied the effects of MDMA on human memory performance.
However, not all studies are equally well-designed, especially when attempting to measure something as insubstantial and as fluctuating as memory performance. So many factors can influence the results - age, sex, education, intelligence, mood, lifestyle, fitness, sleeping pattern, diet, alcohol, drug use, even time of day.
The best studies attempt to filter out these factors by carefully matching the Ecstasy-users with their non-Ecstasy-using 'controls'. A majority of Ecstasy studies, for example, have failed to factor out cannabis use, which has a significant effect itself on memory performance. Others have used to few subjects, or have only studied heavy users.
Of the major studies carried out to date (April 2001) on the effects of Ecstasy on memory performance, only two - Gouzoulis-Mayfrank and Semple - are worth examining closely.