Heavy weed use may be far more dangerous than people realise, according to a pair of studies published in JAMA Network Open.

People diagnosed with cannabis use disorder (CUD) may face nearly triple the risk of death over five years compared to those without the disorder, according to a large study published Feb. 6.

The study, conducted in Ontario, Canada, found that people treated for CUD in hospitals or emergency rooms were 10 times more likely to die by suicide than those in the general population.

They were also significantly more likely to die from trauma, drug poisoning and lung cancer, researchers found.

A separate study—published Feb. 4—linked rising cases of psychosis and schizophrenia in Canada to CUD since the country legalised recreational marijuana in 2018.

Researchers suspect C.U.D. is even more widespread than the data indicate.

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

"Our estimate is that for every person treated for C.U.D. there are another three who didn't seek care," lead author Dr. Daniel Myran, an assistant professor of family medicine at the University of Ottawa, told The New York Times. "So this is not just CUD, but bad enough that they sought care for it."

The study couldn't confirm whether cannabis itself directly increased the risk of death, or if it was related to lifestyle and health factors common among heavy users, The Times reported.

"Either way, this group is really, really high risk, and could benefit from intervention and monitoring and prevention," Myran added.

The same team also looked at how Canada's 2018 legalisation 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:

"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 than what previous generations used.

"Many people think, 'Oh, cannabis is not harmful—it's organic, it's natural; how great,'" Dr. Laura Bierut, a psychiatrist at Washington University School of Medicine in St. Louis who wrote an editorial accompanying the study of death risk, told The Times.

"It is a public health threat just like alcohol," she added.

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