Investigators at the Rudolf Magnus Institute of Neuroscience assessed brain function in "frequent but relatively moderate" cannabis users in the domains of working memory and selective attention using functional magnetic resonance imagining (fMRI).

"No evidence was found for long-term deficits in working memory and selective attention in frequent cannabis users after one week of abstinence" compared to non-using healthy controls, authors concluded. "Furthermore, cannabis users did not differ from controls in terms of overall patterns of brain activity in the regions involved in these cognitive functions."

Previous trials on cannabis use and cognition have reached similar conclusions. An October 2004 study published in the journal Psychological Medicine examining the potential long-term residual effects of cannabis on cognition in monozygotic male twins reported "an absence of marked long-term residual effects of marijuana use on cognitive abilities."

A 2003 meta-analysis published in the Journal of the International Neuropsychological Society also "failed to reveal a substantial, systematic effect of long-term, regular cannabis consumption on the neurocognitive functioning of users who were not acutely intoxicated," and a 2002 clinical trial published in the Canadian Medical Association Journal determined, "Marijuana does not have a long-term negative impact on global intelligence."

For more information, please contact Paul Armentano, NORML Senior Policy Analyst, at (202) 483-5500. Full text of the study, "Long-term effects of frequent cannabis use on working memory and attention: an fMRI study," will appear in the journal Psychopharmacology. A summary of clinical studies assessing the impact of cannabis on cognition is available online at: http://www.norml.org/index.cfm?Group_ID=6812