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Canada’s legalization of cannabis has been linked to an increase in schizophrenia cases, according to new research published in JAMA Network Open.
A Concerning Trend
A study analyzing electronic medical records of over 13.5 million residents of Ontario found that the number of new schizophrenia cases associated with cannabis use disorder (CUD) nearly tripled after cannabis was legalized for both medical and recreational use.
Dr. Daniel Myran of the Ottawa Hospital Research Institute, a lead investigator of the study, noted, “There has been a lot of research on the association between cannabis use and schizophrenia, and one of the main concerns about cannabis legalization is whether it might result in increases in cases of schizophrenia.”
The study tracked three policy periods: before legalization (2006-2015), after medical cannabis legalization (2015-2018), and after nonmedical cannabis legalization (2018-2022). The findings showed that while 3.7% of schizophrenia cases were linked to CUD before legalization, this number rose to 10.3% after legalization, with young men aged 19-24 being most affected. Additionally, hospital visits due to CUD surged by 270% following legalization.
Public Health Implications
Myran emphasized that high-potency cannabis and increased regular use pose significant public health challenges. He cautioned that, despite growing social acceptance of cannabis, risks remain, particularly for younger individuals. “Just because cannabis is now legal and the social norms are changing doesn’t mean that there is no risk, particularly in younger people,” Myran said, drawing parallels with alcohol and tobacco, which are legal but still carry serious health risks.
The study does not conclude whether heavy cannabis use directly causes schizophrenia, but it reinforces previous findings that frequent cannabis use can accelerate schizophrenia onset and worsen symptoms in predisposed individuals.
A Global Concern
Dr. Jodi Gilman from Massachusetts General Hospital and Harvard Medical School, in an invited commentary, highlighted the importance of long-term epidemiological studies in evaluating the mental health impact of cannabis legalization.
“As legalization of cannabis becomes more widespread, a natural experiment of population exposure to commercial cannabis markets is occurring,” Gilman wrote, stressing the need for studies that consider long-term effects, potency levels, and vulnerable subpopulations.
The Need for Continued Research
The study was funded by the Canadian Institutes of Health Research and ICES, with support from the Ontario Ministry of Health. The researchers acknowledge that further studies are required to fully understand the long-term mental health implications of cannabis legalization.
Disclaimer:
This article is for informational purposes only and does not constitute medical or legal advice. The findings discussed are based on the cited research and should not be interpreted as definitive proof of causation. Readers are encouraged to consult healthcare professionals for personalized medical guidance.
