Neuropsychological performance in long-term cannabis users

Background: Although cannabis is the most widely used illicit drug in the U nited States, its long-term cognitive effects remain inadequately studied. Methods: We recruited individuals aged 30 to 55 years in 3 groups: (1) 63 c urrent heavy users who had smoked cannabis at least 5000 times in their liv es and who were smoking daily at study entry; (2) 45 former heavy users who had also smoked at least 5000 times but fewer than 12 times in the last 3 months and (3) 72 control subjects who had smoked no more than 50 times in their lives. Subjects underwent a 28-day washout from cannabis use, monitor ed by observed urine samples. On days 0, 1, 7, and 28, we administered a ne uropsychological test battery to assess general intellectual function, abst raction ability, sustained attention, verbal fluency, and ability to learn and recall new verbal and visuospatial information. Test results were analy zed by repeated- measures regression analysis, adjusting for potentially co nfounding variables. Results: At days 0, 1. and 7, current heavy users scored significantly belo w control subjects on recall of word lists, and this deficit was associated with users' urinary 11-nor-9-carboxy-Delta9-tetrahydrocannabinol concentra tions at study entry. By day 28, however, there were virtually no significa nt differences among the groups on any of the test results, and no signific ant associations between cumulative lifetime cannabis use and test scores. Conclusion: Some cognitive deficits appear detectable at least 7 days after heavy cannabis use but appear reversible and related to recent cannabis ex posure rather than irreversible and related to cumulative lifetime use.