High-potency marijuana increases risk of psychosis in teenagers

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The new study Age-dependent associations between cannabis use and risk of psychosisr A study published in the journal Psychology and Medicine estimated that teens who use marijuana are 11 times more likely to develop a mental disorder than teens who don't use marijuana.

The findings suggest that the link between cannabis and psychiatric disorders may be stronger than previous studies have shown, which relied heavily on older data from a time when cannabis was less potent than it is today. For reference, the average potency of cannabis THC in Canada has increased from about 1 percent in 1980 to 20 percent in 2018.

Researchers from the Centre for Addiction and Mental Health (CAMH), University of Toronto, and ICES linked data from a recent population-based survey of more than 11,000 young people in Ontario, Canada, with health service utilization records, including hospitalizations, emergency department (ED) visits, and outpatient visits.

This study is the first to demonstrate an age-dependent association between self-reported cannabis use and subsequent diagnosis of a psychiatric disorder and contributes to the growing body of research on cannabis-related mental health risks.

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

Among teens who are hospitalized or visit the emergency department for a psychiatric disorder, roughly five in six report having previously used cannabis. McDonald points out that “while the majority of young people who use cannabis do not develop a psychiatric disorder, these data suggest that most young people diagnosed with a psychiatric disorder are likely to have a history of cannabis use.”

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

However, the findings raise growing concerns about cannabis use, especially in the early days after legalization.

On 22 March 2024, the Federal Minister for Health Final report of the Legislative Review The report focused on identifying progress towards achieving the objectives of the Cannabis Act and priority areas for improving the functioning of the Act. The report included several recommendations to limit the harms of cannabis, including:

• Reinstate health warning messages about the serious mental health risks associated with cannabis, including psychosis and schizophrenia.
• Support the development and implementation of evidence-based school prevention programs and other interventions to reduce the prevalence of youth cannabis use.
• Take steps to reduce the risks associated with cannabis products with high THC content.
• Take action against producers and distributors who do not comply with rules to protect young people

” Cannabis Law “In light of this latest research, the need for legislative review seems even more urgent,” said Dr Leslie Buckley, head of CAMH's addictions unit. “We are seeing first-hand the devastating and irreversible impacts that cannabis use has on young people's brains. Healthcare professionals, educators, lawmakers, parents and young people all have a critical role to play in mitigating these impacts through education, policy and prevention strategies.”

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

reference: McDonald AJ, Kurdyak P, Rehm J, Roerecke M, Bondy SJ. Age-dependent associations between cannabis use and risk of psychiatric disorders. Psychomed2024:1-11. doi: 10.1017/S0033291724000990

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