• Posted February 5, 2025

Weed Use Tied To Increase in Schizophrenia

Schizophrenia cases associated with problematic weed use have skyrocketed in the wake of Canada's legalization of marijuana, a new study says.

The proportion of schizophrenia cases associated with cannabis use disorder nearly tripled, rising from 4% pre-legalization to 10%, according to findings published Feb. 4 in JAMA Network Open.

“We found that there have been concerning increases over time in the percentage of people with a new schizophrenia diagnosis who had received care for a cannabis use disorder before their diagnosis,” lead researcher Dr. Daniel Myran, chair of social accountability at the University of Ottawa, said in a news release.

For the study, his team tracked the health of Ontario residents between the ages of 14 and 65 from 2006 through 2022. That period spanned Canada's legalization of medical marijuana in 2015 and then recreational use in 2018.

A total of 118,650 people had an emergency room visit or a hospitalization for cannabis use disorder during the study period, results show.

The number of people who required hospital care linked to weed use jumped 270% from before legalization to after recreational legalization, researchers found.

Results also showed that 10,583 (9%) of people with cannabis use disorder developed schizophrenia, compared with 80,523 (0.6%) of people without problematic weed use.

Overall, the percentage of new cases of schizophrenia in people who’d been previously treated for weed use increased from 7% to 16%

Researchers estimate that about 10% of new schizophrenia cases could have been prevented if people with weed use that landed them in the hospital had quit toking.

In 14- to 24-year-old men, that percentage rose to 18%, researchers said.

“Our study highlights the growing public health challenge posed by the combination of increasingly high-potency cannabis and rising regular cannabis use,” Myran said.

The study does not settle ongoing debate over whether heavy weed use causes schizophrenia, the researchers noted.

However, they argue that heavy use can worsen symptoms and prognosis for people living with schizophrenia.

“The tripling of schizophrenia cases associated with a cannabis use disorder over the past 17 years and rising cases of psychosis underscores the urgent need for targeted prevention strategies, particularly for younger populations who appear to be at the greatest risk,” Myran concluded.

More information

The National Institute on Drug Abuse has more about marijuana.

SOURCE: Institute for Clinical Evaluative Sciences, news release, Feb. 4, 2025