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Review
. 2016 Sep;42(5):1262-9.
doi: 10.1093/schbul/sbw003. Epub 2016 Feb 15.

Meta-analysis of the Association Between the Level of Cannabis Use and Risk of Psychosis

Arianna Marconi  1 , Marta Di Forti  1 , Cathryn M Lewis  2 , Robin M Murray  1 , Evangelos Vassos  3
Affiliations
Review

Meta-analysis of the Association Between the Level of Cannabis Use and Risk of Psychosis

Arianna Marconi et al. Schizophr Bull. 2016 Sep.

Abstract

Cannabis use has been reported to induce long-lasting psychotic disorders and a dose-response relationship has been observed. We performed a systematic review of studies that investigate the association between the degree of cannabis consumption and psychosis and a meta-analysis to quantify the magnitude of effect. Published studies were identified through search of electronic databases, supplemented by manual searches of bibliographies. Studies were considered if they provided data on cannabis consumption prior to the onset of psychosis using a dose criterion (frequency/amount used) and reported psychosis-related outcomes. We performed random effects meta-analysis of individual data points generated with a simulation method from the summary data of the original studies. From 571 references, 18 studies fulfilled inclusion criteria for the systematic review and 10 were inserted in the meta-analysis, enrolling a total of 66 816 individuals. Higher levels of cannabis use were associated with increased risk for psychosis in all the included studies. A logistic regression model gave an OR of 3.90 (95% CI 2.84 to 5.34) for the risk of schizophrenia and other psychosis-related outcomes among the heaviest cannabis users compared to the nonusers. Current evidence shows that high levels of cannabis use increase the risk of psychotic outcomes and confirms a dose-response relationship between the level of use and the risk for psychosis. Although a causal link cannot be unequivocally established, there is sufficient evidence to justify harm reduction prevention programs.

Keywords: dose response; drug use; psychotic disorders; schizophrenia; systematic review.

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Figures

Fig. 1.
Fig. 1.
Flow diagram of study selection process.
Fig. 2.
Fig. 2.
Estimated risk ratio of psychosis by level of cannabis use in original studies.
Fig. 3.
Fig. 3.
Forest plots including subgroup analyses of the odds ratio of psychosis in the most severe cannabis users. (A) Divided by study design (cohort and cross-sectional). (B) Divided by outcome measure (diagnosis of psychotic disorder and presence of psychotic symptoms).
See this image and copyright information in PMC

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