The current study was conducted to test the association between persistent cannabis use and neuropsychological decline. In addition, the study sought to determine whether decline is concentrated among adolescent-onset cannabis users. Participants were members of the Dunedin Study, a prospective study of a birth cohort of 1,037 individuals followed from birth (1972/1973) to age 38 years. Cannabis use was ascertained in interviews at ages 18, 21, 26, 32, and 38 years. Neuropsychological testing was conducted at age 13 years, before initiation of cannabis use, and again at age 38 years, after a pattern of persistent cannabis use had developed. Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. More cognitive problems were also reported for persistent cannabis users. Impairment was concentrated among adolescentonset cannabis users with more persistent use being associated with greater decline. Furthermore, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. The authors concluded that cannabis might have neurotoxic effects on the adolescent brain and that these results highlight the importance of prevention and policy efforts targeting adolescents. Proc Natl Acad Sci U S A. 2012 Aug 27. PMID: 22927402
