Cannabis, psychosis, and violence: case reports and comprehensive evidence review

Cannabis use, especially high-potency products with THC concentrations above 10%, has been linked to rising psychosis cases from 1995 to 2010. Psychosis has multiple causes including genetics, childhood adversity, and drug use. This perspective argues that cannabis-associated violence deserves more attention, presenting high-profile media cases where THC was the only substance involved or cannabis use preceded psychosis and violence. Toxicology often fails to test for THC. The evolving evidence on cannabis, psychosis, and violence should inform medical screening, law enforcement, and policy.

Study at a glance

Abstract

Cannabis is one of the most widely used psychoactive substances, with higher use rates in countries that have implemented policies to legalize medical or recreational use. Following the development of cannabis products with concentrations well above 10% THC (high potency, delta-9 tetrahydrocannabinol), the number of psychosis cases has also increased. Cannabis-attributable psychosis cases increased from 1995 to 2010, and speculates that increased cannabis potency might have contributed. Psychosis is a complex disorder regarding its etiology, with multiple factors well documented and accepted, including genetic predisposition, adverse childhood events, and recreational drug use. Cannabis is a potential contributing factor to psychosis or subsequent violence, but toxicology in such cases often does not include THC. Here we provide a perspective to argue that greater attention should be put toward cannabis-associated violence. We present several high-profile cases of violence reported in main-stream media, where the only substance involved is tetrahydrocannabinol (THC) or the involvement of cannabis was noted in the person’s history. Some of these cases have well-documented cannabis use preceding the onset of psychosis and violence, yet toxicology was not done or did not include THC. The scientific evidence regarding the relationship between cannabis, psychosis, and violence continues to evolve and should be part of medical screening, law-enforcement concerns, and policymaking.