Semple DM, Ebmeier KP, Glabus MF, O'Carroll RE, Johnstone EC (1999) Br J Psychiatry 175: 63-6

read the entire study here

the subjects
Ten male users between 18 - 35 with an average lifetime consumption of 672 Ecstasy pills and a minimum of 50, abstinent from E for an average of 18 days.

Matched to 10 control subjects, of the same age, sex, education, and drug use (tobacco, alcohol, cannabis and amphetamines) bar ecstasy.

the tests
Several standard memory tests but mainly - and importantly - brain imagining, to measure serotonin transporter binding, i.e. how effectively the serotonin system was working in their brains.

the results
Increasing lifetime exposure to Ecstasy was clearly linked with decreasing memory performance. Serotonin transporter binding was significantly lower in Ecstasy users in several brain areas, meaning the serotonin system was impaired.

The time of abstinence from Ecstasy did appear to improve serotonin transporter levels, implying that neurotoxicity may be temporary and recover with time.