The Pharmaceutical Journal
Vol 268 No 7190 p385-391
23 March 2002

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Journal of the American Medical Association (jama.ama-assn.org)

Cannabis use can cause lasting memory problems

Memory problems experienced by long-term, heavy users of cannabis persist beyond the period of intoxication, researchers from the United States and Australia confirm.

They conducted a retrospective study among 102 users of cannabis and compared neuropsychological test results with those for 33 non-users. Subjects who used cannabis were defined as either long-term users (mean 23.9 years of use) or shorter-term users (mean 10.2 years of use).

The researchers found that long-term cannabis users performed less well on tests of memory and attention than shorter-term users and non-users. "The fact that the frequency of use was near daily among long- and shorter-term users suggests that the duration of cannabis use is a more salient contributor to the development of cognitive impairment than quantity or frequency of use," say the researchers.

They add that impairment develops gradually but may only be clinically significant after one to two decades of cannabis use. "The risk to most [users of medicinal cannabis] is likely to be small," they conclude (JAMA 2002;287:1123).