Heavy cannabis users face substantially higher mortality risks and increased rates of psychosis, according to two recent studies published in JAMA Network Open that challenge perceptions about marijuana's safety profile.
Researchers from the University of Ottawa found that individuals diagnosed with cannabis use disorder (CUD) have a mortality rate nearly three times higher than the general population over a five-year period. The comprehensive study, which analyzed health records of 106,994 people diagnosed with CUD in Ontario, Canada between 2006 and 2021, revealed alarming statistics about the potential dangers of heavy cannabis use.
"Our estimate is that for every person treated for CUD there are another three who didn't seek care," said lead author Dr. Daniel Myran, assistant professor of family medicine at University of Ottawa. "So this is not just CUD, but bad enough that they sought care for it."
Mortality Risk Significantly Higher Among Cannabis Users
The data showed that 3.5% of people with CUD died within five years of treatment, compared to just 0.6% of a similar group without the disorder. Even after accounting for other risk factors including mental illness, heart disease, cancer, and other substance use, CUD patients still had a 2.8 times higher risk of death.
Particularly concerning was the finding that CUD patients were 10 times more likely to die by suicide than those in the general population. They also faced significantly higher risks of death from trauma, drug poisoning, and lung cancer. Young adults aged 25 to 44 were identified as facing the highest risk of premature death.
Rising Psychosis Cases Following Cannabis Legalization
A companion study by the same research team examined how Canada's 2018 legalization of recreational cannabis affected rates of psychosis and schizophrenia. By analyzing data across three periods—2006-2015 (pre-legalization), 2015-2018 (transitional period), and 2018-2022 (post-legalization)—researchers documented a troubling trend.
While the overall rate of schizophrenia remained stable, the percentage of cases linked to cannabis use disorder jumped dramatically from 3.7% to 10.3% after legalization. Additionally, the rate of psychosis without schizophrenia nearly doubled during this period. Young adults aged 19 to 24 were most affected by these mental health impacts.
"This is a period of the life span when the brain is still developing and still vulnerable to the effects of cannabis," explained Jodi Gilman, associate professor of psychiatry at Harvard Medical School, who wrote a commentary on the study. "Psychosis and schizophrenia are also known to develop in young adulthood, so you have a double hit."
Medical Cannabis Users Not Immune to Addiction Risks
A separate study published in JAMA Psychiatry in January 2025 further complicates the cannabis safety picture by revealing that medical marijuana users face equal or higher addiction risks compared to recreational users.
The research, led by Dr. Nora Volkow, director of the National Institute on Drug Abuse, analyzed data from nearly 73,000 adults who reported recent cannabis use. Approximately 35% of all users met criteria for cannabis use disorder, with medical users showing higher rates of problematic use in several demographic groups.
For example, about 14% of male medical users aged 18-34 had severe cannabis use disorder, compared with 8% of recreational users in the same demographic. Medical marijuana patients also used cannabis more frequently—40% to 70% more days per year on average than recreational users.
"These findings suggest that medically recommended cannabis is not associated with reduced addiction risk compared with nonmedical use," the researchers concluded. "Clinicians should consider addiction risk before recommending medical cannabis and, if they do, should monitor for CUD emergence."
Today's Cannabis More Potent Than Previous Generations
Experts emphasize that modern cannabis products are significantly more potent than what previous generations used, which may contribute to the observed health risks.
"Many people think, 'Oh, cannabis is not harmful—it's organic, it's natural; how great,'" said Dr. Laura Bierut, a psychiatrist at Washington University School of Medicine in St. Louis. "It is a public health threat just like alcohol."
While the studies couldn't definitively establish whether cannabis directly increases mortality risk or if the association relates to lifestyle and health factors common among heavy users, the findings highlight the need for greater awareness of potential harms associated with both recreational and medical cannabis use.
As cannabis legalization continues to expand globally, these studies underscore the importance of public health monitoring, addiction prevention strategies, and targeted interventions for vulnerable populations, particularly young adults whose developing brains may be most susceptible to cannabis-related harms.
