The relative contributions of ecstasy and cannabis to cognitive impairment

Rationale: (+/-)-3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy'), a com monly used recreational drug, has typically been found to be related to poo r cognitive function in humans. However, cannabis consumption may not have been adequately controlled for in these studies. Objective: The present stu dy was designed to further elucidate the relation between MDMA and cannabis in cognitive impairment. Methods: Subjects who had used neither MDMA nor c annabis (controls; n=31), cannabis but not MDMA (cannabis users; n=18) and both MDMA and cannabis (MDMA/cannabis users; n=11) were compared on a batte ry of neuropsychological tests. Results: The cannabis and MDMA/cannabis gro ups did not differ on any of the tests, whereas the combined cannabis and M DMA/cannabis groups performed more poorly than controls on tests of memory, learning, word fluency, speed of processing and manual dexterity. Further, apart from speed of processing where higher MDMA consumption predicted slo wer processing, covariate analysis revealed that the deficits were more clo sely related to cannabis than MDMA usage. Conclusion: The results suggest t hat cannabis is an important confound in studies of MDMA-related cognitive impairment, and that previously reported cognitive impairment in MDMA users may have been caused by coincident cannabis use.