Cannabis use in adolescence and risk of psychosis: Are there factors that moderate this relationship? A systematic review and meta-analysis.

Background: Previous research has reported increased risk for psychosis among individuals who use cannabis during adolescence. We conducted a systematic review and meta-analysis to investigate the interaction between adolescent cannabis use and other factors in moderating risk for psychosis later in life. Method: We searched four electronic databases in June 2020 for articles that assessed adolescent cannabis use, had psychosis as an outcome and analyzed for the association between adolescent cannabis use and psychosis. Analysis was done using random-effects meta-analysis and narrative synthesis. Results : A total of 63 studies were included in the narrative review and 18 studies were included in the meta-analysis. Adolescent cannabis use was found to increase risk for psychosis (RR = 1.71 (95%CI, 1.47-2.00, p  < 0.00001) and predict earlier onset of psychosis. The following factors moderate the relationship between cannabis use and the risk of psychosis: age of onset of cannabis use, frequent cannabis use, exposure to childhood trauma, concurrent use of other substances and genetic factors. Conclusion: Adolescent cannabis use is associated with an increased risk for psychosis later in life. In addition, there are factors that moderate this relationship; therefore there is a need for research to assess the interaction between these factors, adolescent cannabis use and psychosis risk.