Cannabis and Psychosis: A Review of the Risk Factors Involved

Cannabis use is associated with the onset of psychotic symptoms, but whether the link is causal remains controversial. This systematic review of 1653 studies identified six risk factors that increase the likelihood of psychosis among cannabis users, ranked by importance: dose-response relationship (quantity, frequency, and duration of use), early age of first use, genetic susceptibility, childhood trauma, cigarette smoking, and urban environment. In contrast, cannabidiol (CBD) is associated with fewer psychotic symptoms and appears to have antipsychotic properties. The authors conclude that further research is needed to establish a clear causal relationship and to determine how much each risk factor contributes to the onset and persistence of psychosis.

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Abstract

Abundant literature suggests the hypothesis that cannabis use leads to the onset of psychotic symptoms. However, the nature of the association and the causal link remain controversial. This review aims to identify the risk factors involved in the etiopathogenesis of psychosis or psychotic features. Our electronic search found 1653 studies published until March 1st 2020. Longitudinal studies and literature reviews were selected if they addressed specifically the issues of the cannabis/psychosis relationship and the eventual risk factors involved. Our systematic review identified six potential risk factors involved in the association. They are, in decreasing importance, the dose-response relationship (quantity, frequency and duration of cannabis use), the early age of cannabis consumption, genetic susceptibility, childhood trauma, cigarette smoking and urban environment. In contrast, a significant inverse relationship exists between cannabidiol (CBD) and psychosis: cannabidiol is associated with less psychotic symptoms and manifests antipsychotic properties. Further studies are needed to establish a clear causal relationship between cannabis and psychosis and to identify the qualitative and quantitative contribution of specific risk factors on its onset and sustainability.