Contribution of cannabis and MDMA ("ecstasy") to cognitive changes in long-term polydrug users

RATIONALE: Establishing whether cognitive changes follow long-term use of MDMA ("ecstasy") in humans has been difficult because of possible confounds with other drug use, particularly cannabis. Convincing evidence may be only obtained using experimental designs that account for such confounds. OBJECTIVE: In the present study, cognitive/behavioural measures were used to investigate whether long-term MDMA use or long-term cannabis use is responsible for the changes sometimes observed in recreational MDMA users. METHOD: Tests of attention and memory were administered to subjects who used both MDMA and cannabis, cannabis only, or neither drug. RESULTS: The main finding was that cannabis users, whether or not they also used MDMA, showed significantly impaired memory function on word free-recall and on immediate and delayed story recall compared to non-users. CONCLUSIONS: The findings highlight the importance of controlling for other drug use (particularly cannabis) when investigating persistent effects of MDMA in humans