The results of a Canadian cohort analysis published in JAMA Psychiatry demonstrated a predominant association of cannabis use frequency and increased symptoms of psychosis.

Canada will legalize the use of cannabis in July of this year, but its potential role in the development of psychiatric disease, such as psychosis, has yet to be established. Although prospective studies have reported an association between cannabis use and later onset of psychosis, the studies failed to assess symptoms of psychosis at more than a single follow-up.

To remedy this, author Josiane Bourque, MSc, of the Department of Psychiatry at the University of Montreal, CHU Sainte-Justine Research Center in Montreal, Quebec, Canada, and colleagues followed a sample of 3720 adolescents over several years. The cohort had a mean age of 12.8 years and 49.1% were female. The sample was drawn from the developmentally informed Co-Venture cohort, which included 76% of seventh grade students in the greater Montreal area. The adolescents agreed to participate in the study and completed a confidential annual web-based survey from age 13 to 16 years. The survey included self-report of cannabis use and symptoms of psychosis. The investigators used random intercept cross-lagged panel models to test causal predominance.

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Significant positive associations were noted at every time point between cannabis use and symptoms of psychosis. The authors noted that one limit of the study was that cannabis use and symptoms of psychosis were not confirmed by a clinician; however, previous studies have shown self-report of symptoms of psychosis to be reliable, with positive predictive values of 80% to 100%.

The authors argue that the association of cannabis use with symptoms of psychosis underscores the need for targeted cannabis use prevention as legalization of the substance moves forward.


Bourque J, Afzali MH, Conrod PJ. Association of cannabis use with adolescent psychotic symptoms [published online June 6, 2018]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2018.1330