Marijuana Clearly Linked to Schizophrenia

According to a pair of studies published in JAMA Network Open, there is a clear link between marijuana use and an increased risk of schizophrenia, with the proportion of new schizophrenia cases linked to "cannabis use disorder" (CUD) nearly tripling since the country's legalization of marijuana.

The study, which analyzed data from over 13.5 million Ontario residents between 2006 and 2022, found that the number of new schizophrenia cases associated with cannabis use disorder increased from 4% to 10% after legalization.

According to a report in U.S. News & World Report:

"When they analyzed Ontario health records from 106,994 people diagnosed with CUD during a hospital or emergency room visit between 2006 and 2021, researchers found:

-3.5% of people with CUD died within five years of treatment, compared to 0.6% of a similar group of people without CUD.

-CUD patients still had a 2.8 times higher risk of death than the general population even after other risk factors like mental illness, heart disease, cancer and other substance use were considered.

-Young adults aged 25 to 44 faced the highest risk of premature death.

The article goes on to report:

The same team also looked at how Canada's 2018 legalization of cannabis affected rates of psychosis and schizophrenia.

Researchers looked at three periods: 2006-2015 (before cannabis legalization); 2015-2018 (amid widening use of medical and non-medical cannabis); and 2018-2022 (after legalization).

While the overall rate of schizophrenia remained stable, researchers found:

-The percentage of cases linked to CUD jumped from 3.7% to 10.3% after legalization.

-The rate of psychosis (without schizophrenia) nearly doubled.

-Young adults aged 19 to 24 were most affected.

“This is a period of the life span when the brain is still developing and still vulnerable to the effects of cannabis,” Jodi Gilman, an associate professor of psychiatry at Harvard Medical School who wrote a commentary about the study, told The Times. Psychosis and schizophrenia are also known to develop in young adulthood, Gilman added, “so you have a double hit.”

Experts warn that today's marijuana is far more potent that what previous generations used."

https://www.usnews.com/news/health-news/articles/2025-02-07/study-links-heavy-cannabis-use-to-higher-death-risk-psychosis