Chronic cognitive impairment in users of 'ecstasy' and cannabis.

MDMA use is commonly accompanied by use of other substances, most notably cannabis. Both MDMA and cannabis have probable effects on cognition. This paper reviews research into long-term effects on cognition which are likely to represent neurotoxicity. Research is hampered by numerous confounds and methodological difficulties. With recent cannabis use there is both an acute and a residual effect on cognition, making it important to have a significant abstinence period from cannabis when studying effects of MDMA in recreational users of both substances. It would appear that MDMA does indeed have subtle long-term effects on complex memory and executive functions that are independent of cannabis and may remain with abstention. This is consistent with evidence of disruption of the serotonin system in animal and human studies. Chronic effects on cognition due to cannabis are less consistently demonstrated, but more sensitive tests including electrophysiological measures have revealed long-term deficits in attention.