New evidence suggests stronger link between teen cannabis use and psychotic disorders

May 22, 2024 (Toronto, Canada) – A new study entitled Age-dependent association between cannabis use and risk of psychotic disorders A paper published in the journal Psychological Medicine estimated that teens who use marijuana are 11 times more likely to develop a psychotic disorder than teens who do not use marijuana. I am.

This finding suggests that the association between cannabis and psychiatric disorders may be stronger than shown in previous studies, which relied primarily on older data from a time when cannabis was less potent than it is now. suggests. For comparison, the average THC (tetrahydrocannabinol) potency of cannabis in Canada has increased from about 1 per cent in 1980 to 20 per cent in 2018.

Researchers from the Center for Addiction and Mental Health (CAMH), University of Toronto, and ICES analyzed recent population-based survey data from more than 11,000 young people in Ontario, Canada, for hospitalization and emergency department (ED) ) with records of medical service usage, such as medical visits. , outpatient visit.

This study is the first to show an age-dependent association between self-reported cannabis use and subsequent diagnosis of psychotic disorders, and adds to the growing body of research on mental health risks associated with cannabis. There is.

“We found a very strong association between cannabis use and risk of psychotic disorders in adolescence. Surprisingly, we found no evidence of an association in young adulthood. '' said lead author Dr. Andre MacDonald. He conducted this study as part of his doctoral training at ICES. CAMH Institute for Mental Health Policy and the University of Toronto. MacDonald is currently a postdoctoral researcher at McMaster University's Peter Boris Centre for Addiction Research and the Michael G. DeGroote Centre for Medical Cannabis Research. “These findings are consistent with neurodevelopmental theories that suggest teens may be particularly vulnerable to the effects of cannabis.”

Approximately 5 in 6 teens who were hospitalized or visited the emergency department for a mental disorder had previously reported marijuana use. “Although the vast majority of teens who use cannabis do not develop a psychotic disorder, these data suggest that most teens diagnosed with a psychotic disorder have a history of cannabis use,” McDonald said. “It's highly likely.”

The researchers could not completely rule out reverse causation, that is, teens with psychotic symptoms may have self-medicated with cannabis before receiving a clinical diagnosis. They also could not account for potentially important factors, such as genetics or trauma history. These limitations make it impossible to say definitively that teen cannabis use causes psychotic disorders. The authors also noted that their estimates are only approximate, suggesting that further research with larger samples is needed.

Nevertheless, this finding raises concerns about cannabis use, especially in the early years after legalization.

On March 22, 2024, the Federal Minister of Health shared: Final report of legislative review This report focuses on progress towards achieving the objectives of the Cannabis Act and identifying priority areas for improving the Act's functioning. The report included several recommendations to limit the harms of cannabis, including:

• Reinstate health warning messages related to serious cannabis-related mental health risks, including psychosis and schizophrenia.
• Support the development and implementation of evidence-based school prevention programs and other interventions to reduce the prevalence of cannabis use among youth.
• Take steps to reduce the risks associated with cannabis products containing higher amounts or concentrations of THC. and
• Taking action against producers and distributors who do not follow rules to protect young people

“The recommendations that emerge from cannabis law In light of this latest research, a legal review seems even more urgent,” said Dr Leslie Buckley, Head of Addictions at CAMH. “We are seeing firsthand the devastating and irreversible effects that cannabis use has on young people’s brains. Healthcare providers, educators, legislators, parents, and young people all need to address these issues through education, policy, and prevention strategies. play an important role in mitigating the impact of

MacDonald added: “Canadian youth are some of the highest users of cannabis in the world. Following the precautionary principle, ultimately we need to do more to prevent early cannabis use. ” he added.

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About Center for Addiction and Mental Health (CAMH)

CAMH is Canada's largest mental health and addictions teaching hospital and one of the world's leading research centers in the field. CAMH combines clinical care, research, education, policy development and health promotion to help transform the lives of people affected by mental illness and addiction. CAMH is fully affiliated with the University of Toronto and is a Pan American Health Organization/World Health Organization Collaborating Center. For more information, visit camh.ca or follow @CAMHnews on X (formerly Twitter).

About ICES

ICES is an independent, nonprofit research and analysis organization that uses population-based health information to generate knowledge on a wide range of medical issues. ICES leads cutting-edge research and analysis that evaluates health policy, delivery, and population outcomes. ICES knowledge is highly valued in Canada and abroad and is widely used by governments, hospitals, planners, and health care providers to make decisions and develop policy regarding health care delivery. For the latest news from ICES, follow us on X (formerly Twitter): @ICESOntario

Media Contact:

hayley clarke
Manager of Media Strategy, CAMH
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Misty Pratt
ICES Senior Communications Associate
[email protected]
613-882-7065