Study Links Rising Schizophrenia Cases to Increased Cannabis Use in Ontario

A recent study has revealed a significant increase in schizophrenia cases linked to cannabis use in Ontario, Canada. Researchers examined over 13.5 million medical records from 2006 to 2022, highlighting a near tripling of such cases as cannabis availability expanded. The findings, published in the journal JAMA Network Open, underscore the potential mental health risks associated with cannabis consumption, particularly following its legalization for recreational use in Canada in 2018

The research indicates that the proportion of new schizophrenia cases in Ontario associated with cannabis use rose from 3.7% before legalization to 10.3% after. This study adds to a growing body of evidence suggesting a connection between heavy cannabis use and mental health disorders such as schizophrenia and psychosis. Daniel Myran, the study's lead author and a researcher at the University of Ottawa, emphasized the increase in schizophrenia diagnoses among individuals previously treated for cannabis use disorders

The study's findings are particularly pronounced among young men aged 19 to 24, with nearly 19% of new schizophrenia cases in this group linked to cannabis use disorder. Myran highlighted the vulnerability of young adults to the neurological effects of cannabis, which can exacerbate the risk of developing psychosis. This aligns with previous international research, including a Danish study published in 2021, which reported similar trends in cannabis-related schizophrenia cases

Experts like Marta Di Forti from King’s College London have praised the Canadian study for its robust methodology and extensive sample size. Di Forti noted the manifestation of psychosis in heavy cannabis users, often characterized by paranoia and social withdrawal. While acknowledging the therapeutic potential of cannabis, she stressed the importance of providing mental health support for those affected by its adverse effects

Despite its significant findings, the study acknowledges limitations, such as the absence of data on genetic and environmental factors that could influence schizophrenia development. Additionally, the research focused only on individuals treated for cannabis use disorders in medical settings, potentially underestimating the broader impact. Jodi Gilman from Harvard Medical School emphasized the need for continued research and public health strategies to mitigate these risks