Exposure to cannabis increases the risk for psychoses ranging from transient psychotic states to chronic recurrent psychosis. Greater dose and earlier age of exposure raise the risk. For some psychosis outcomes, evidence supports some causality criteria, but reverse causality and confounders cannot be ruled out. Cannabis is neither necessary nor sufficient to cause psychosis; it is likely one of multiple causal components. In those with established psychosis, cannabis negatively affects the illness course and expression. Emerging evidence suggests alterations in the endocannabinoid system in psychotic disorders. Delaying or eliminating cannabis exposure could potentially reduce psychosis rates, especially in high-risk individuals.
From 2006 to 2016, the incidence rate of cannabis-induced psychosis in Denmark rose from 2.8 to 6.1 per 100,000 person years. A corresponding increase occurred in dual diagnoses of schizophrenia with cannabis use disorder, while alcohol-induced psychosis decreased. Other substance-induced psychoses showed no clear trend. The rise in cannabis-induced psychosis parallels increases in both cannabis use and the THC content of cannabis, and changes in diagnostic practice do not appear to account for the increase.