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The cumulative use of cannabis over several decades is not associated with a significantly elevated risk of either psychiatric disorders, cognitive decline, or other adverse psychosocial outcomes, according to longitudinal data published in the Journal of Psychopathology and Clinical Science.

Investigators affiliated with the University of Minnesota and the University of Colorado assessed the long-term impact of cannabis use on psychiatric and psychosocial outcomes in a sample of more than 4,000 adult twins. Subjects were assessed from 1994 to 2021. 

“This study suggests that lifetime exposure to cannabis has few persistent effects on mental health and other psychosocial outcomes,” researchers reported. “We did not identify within-pair differences in cognitive ability. … Cannabis consumption did not predict within-pair differences in psychoticism.”

Researchers cautioned that heavy cannabis use could elevate the risk of so-called ‘cannabis use disorder,’ tobacco use, and experimentation with other controlled substances.

The study’s authors concluded: “Broadly speaking, our results do not support a causal relationship between lifetime average cannabis frequency and most of the substance use, psychiatric, and psychosocial outcomes assessed here. Rather, genetic and familial confounding most likely explain the relationships between cannabis use and the negative outcomes associated with it. … The lack of within-pair effects, or small effects for those existing within-pair differences, in our primary outcome suggest that cumulative cannabis use does not have large, or lasting effects on many psychosocial outcomes.”

Full text of the study, “Limited psychological and social effects of lifetime cannabis use frequency: Evidence from a 30-year community study of 4,078 twins,” appears in the Journal of Psychopathology and Clinical Science.

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