Cannabis use is increasingly normalized, and psychosis is a major adverse health outcome. This review identifies risk factors for cannabis-related psychosis: genetic predisposition, mental health and substance use histories, early age of first use, high frequency of use, high THC potency, mode of use, and co-use of other substances. The protective effects of CBD are uncertain. Continuous cannabis use may worsen psychosis treatment and medication effects. Combinations of risk factors further amplify the odds of adverse psychosis outcomes. Reducing these risk factors, short of abstinence, may decrease the risk of psychosis and protect cannabis users' health.
Cannabis legalization and commercialization are increasing worldwide, with rising tetrahydrocannabinol potency linked to greater risks of dependence and psychosis. Dependence risk has risen from 9% to near 30% as potency increased. Daily use of high-potency cannabis raises psychosis risk up to 9-fold, comparable to the lung cancer risk from smoking 30 cigarettes daily. Evidence from prospective studies shows a causal relationship between cannabis use and later schizophrenia-like psychosis, not explained by confounding factors or reverse causation. Adolescents and those with a family history of psychosis are especially vulnerable. The cannabis industry's marketing and lobbying echo tactics used by the tobacco industry to downplay health harms.