The use of cannabis has increased significantly over the last few decades, most notably in young adults, with 18.4% of adolescents and 32.6% of college age students in North America reporting the use of cannabis during the past 30 days. As more states have legalized the medical and/or recreational use of marijuana, we are seeing increased usage among young adults, coupled with a steady increase in the availability of cannabis-containing products and an overall increase in the potency of these products.
We are particularly concerned about the growing use of cannabis, and the associated perception that it is a recreational drug with little risk of harm, among young adults. In terms of neurodevelopment, late adolescence and early adulthood is a particularly vulnerable time, as the brain is undergoing extensive changes, including the development of higher cognitive functioning and increases in connectivity between various regions of the brain.
Studies carried out in adults have observed that cannabis use during this vulnerable neurodevelopmental period may result in long-term changes in brain structure, function, and connectivity, manifested as deficits in cognitive performance, motivation, and emotional processing.
Other studies have indicated that cannabis use in adolescents and young adults may be associated with an increased risk of psychosis. While the etiology of psychotic disorders is not well understood and is clearly influenced by multiple genetic and environmental factors, there has been increased concern regarding the role that cannabis use may play as a potentially preventable environmental risk factor for psychosis.
The relationship between cannabis use and psychotic disorders is complicated. Does using cannabis trigger or cause psychosis? Or are those with (or at risk for) a psychotic disorder more likely to use cannabis? It has been difficult to disentangle genetic from environmental factors, and there is some research to suggest a common genetic pathway for both psychotic disorders and cannabis use. Nonetheless, we cannot ignore a growing body evidence linking cannabis use and psychosis.
Multiple studies have observed a strong dose-dependent association between cannabis use and psychotic disorder. Multiple factors may also modulate the association between cannabis use and risk for psychosis:
Frequency of Use: In youth, greater frequency of cannabis use was associated with increased risk of psychotic disorder, specifically a 50% to 200% increase in risk in those who used most heavily.
Potency of Cannabis: People who use cannabis and later develop schizophrenia present with psychotic symptoms at a significantly younger age than cannabis non-users. Youth who used cannabis with high THC levels held a 3-fold increase in risk of a psychotic disorder compared to those who never used cannabis.
Age at First Cannabis Use: Earlier age at onset of cannabis use predicted earlier onset of psychotic symptoms.
Vulnerability to Psychotic Illness: Most studies assessing vulnerability to psychotic illness following cannabis use have not taken into account additional risk factors for psychotic illness, including family history, childhood trauma, use of tobacco, and urbanicity. These factors may, together, interact to increase the risk of psychosis.
In one of the largest studies to date including 901 people presenting with their first episode of psychosis (Di Forti et al, 2019), daily cannabis use was associated with a fourfold increase in risk of psychotic illness compared to never users. For daily users of high-potency THC cannabis, the risk was nearly 5 times higher.
Given the current changes in the legal climate and shifting attitudes toward the use of cannabis, we are likely to see increasing numbers of adolescents and young adults with cannabis use disorder and other problems related to the use of cannabis. Especially concerning is the commercialization of increasingly potent THC products and new, more accessible routes of administration, including vaped and edible products. Younger people and those with genetic risk for psychosis are at increased risk of psychosis, especially with heavier use and exposure to more potent products.
Wright and colleagues urge clinicians to screen regularly for cannabis use and to help educate their patients regarding the risks associated with cannabis use. They also highlight the need for educational campaigns and prevention programs in order to better inform vulnerable groups of the risks of cannabis use. Similar to previous campaigns educating the public about the risks of using alcohol during pregnancy, the messaging should clearly communicate that cannabis is legal, but not safe, for younger users.
This article was based on a review published by Wright and colleagues (2020) in the January issue of Child and Adolescent Psychiatric Clinics of North America on Psychosis in Children and Adolescents: A Guide for Clinicians.
Read More:
Di Forti M, Quattrone D, Freeman TP, Tripoli G, et al.The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. Lancet Psychiatry. 2019 May;6(5):427-436.
Wright A, Cather C, Gilman J, Evins AE. The Changing Legal Landscape of Cannabis Use and Its Role in Youth-onset Psychosis. Child Adolesc Psychiatr Clin N Am. 2020 Jan;29(1):145-156.
Abigail Wright, PhD, is a Postdoctoral Fellow at the Center of Excellence (COE) for Psychosocial and Systemic Research at Massachusetts General Hospital.
Cori Cather, PhD is the director of the MGH Center of Excellence for Psychosocial and Systemic Research and an associate professor at Harvard Medical School.
Jodi Gilman, PhD is the Director of Neuroscience at the MGH Center for Addiction Medicine and is an assistant professor at Harvard Medical School.
Eden Evins, MD, MPH, is the Cox Family Professor of Psychiatry in the field of Addiction Medicine, Harvard Medical School and the founder and Director of the Center For Addiction Medicine at MGH.
