A recent study in JAMA Network Open found that the population-attributable fraction of cannabis use disorder (CUD) that was associated with schizophrenia in Ontario, Canada, increased from 3.7% prior to the legalization of marijuana to 10.3% after legalization. This represented a statistically significant increase.
The authors explained that this increase occurred alongside Canada’s liberalization of marijuana laws. Drawing on various sources, they added:
The potency of marijuana doubled over the study’s time frame; more than 70% of dried marijuana that is sold in Ontario now exceeds 20% THC.
Emergency department visits in Ontario for cannabis-induced psychosis and CUD have increased.
Between 2006 and 2022, the percentage of Ontario residents aged 18 years or older who reported past-year cannabis use and patterns placing them at moderate or high risk of experiencing social problems or cannabis dependence increased by 145.5% and 223.3%, respectively.
The authors noted, “Our results, and those of others, highlight that the association between CUD and schizophrenia may be particularly elevated among younger males, in whom an estimated 18.9% of incident schizophrenia cases were associated with CUD by the end of the study.”
Dr. Daniel Myran, the study’s first author and an affiliate of the University of Ottawa, said in a statement, “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.”
