Frequent cannabis use linked to increased risk of psychosis
Studies in Europe and the USA have uncovered a clear association of frequent non-medical cannabis use, and use of high-potency (high THC) cannabis with psychotic disorders. The American study found that: “Self-reported psychotic disorders were significantly more prevalent among participants with any nonmedical cannabis use than those without (2001–2002: 1.65% compared with 0.27%; 2012–2013: 1.89% compared with 0.68%).” Also, self-reported psychotic disorder seems to be increasing over time among frequent/heavy cannabis users.
The European study, conducted in 11 sites in Europe and one in Brazil, found that: “29.5% of the patients with first-episode psychosis had used cannabis every day, compared with 6.8% of controls. After adjusting for factors such as socioeconomic status and recreational use of other drugs, they found that people who used cannabis every day were three times more likely to have a diagnosis of first-episode psychosis than those who had never used cannabis and nearly five times more likely if they used high-potency cannabis daily.”
People are becoming accustomed to thinking of marijuana as a safe substance and a kind of panacea drug, “probably good for anything you’ve got”, and these results should be sobering. Certainly, there are medical uses for cannabis, and more are being revealed by research, but cannabis-use disorder is a real thing, and, as these studies show, psychiatric effects of heavy cannabis use can be anything but benign.
It is important to keep in mind that research into the effects of marijuana use is, in some ways, still in its infancy, and we should keep monitoring the research to understand what is being learned over time. Patients should not be shy about sharing their cannabis exposure with health care practitioners, particularly in the mental health field. Psychiatrists and psychologists should remind themselves to give more attention to questioning patients about marijuana use, especially in regions where its legal status is in flux, or is opening up to more legalization.
For more information:
Di Forti et al. The Contribution of Cannabis Use to the Variation in the Incidence of Psychotic Disorder Across Europe (EU-GEI): A Multicentre Case-Control Study. The Lancet Psychiatry. March 19, 2019. DOI:https://doi.org/10.1016/S2215-0366(19)30048-3
Livne, Ofir et al. Association of Cannabis Use–Related Predictor Variables and Self-Reported Psychotic Disorders: U.S. Adults, 2001–2002 and 2012–2013. The American Journal of Psychiatry. 14 Oct 2021. https://doi.org/10.1176/appi.ajp.2021.21010073