A potential link between cannabis use and new cases of schizophrenia is in the spotlight again after a study found an alarming increase.
The study included all Ontario residents eligible for universal health care – more than 13.5 million individuals aged 14 to 65. It found the proportion of new cases of schizophrenia associated with a cannabis use disorder (CUD) had risen from 4% pre-legalization to 10% after cannabis legalization.
Schizophrenia is a serious mental health condition that may result in hallucinations, delusions, and disorganized thinking and behavior. CUD is a condition where a person has a problematic pattern of cannabis use causing negative impacts in their life, but they continue to use it.
The study found total of 118,650 individuals had an emergency department visit or hospitalisation for a CUD, which works out to 0.9% of Ontario’s population. Over the study period, 10,583 – 9% of individuals – with CUD developed schizophrenia compared to 80,523 (just 0.6%) of individuals without CUD.
While the study’s authors stress the findings do not settle ongoing debates about whether heavy cannabis use can trigger schizophrenia, they say it worsens symptoms and the prognosis for those living with the condition.
“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,” . says Dr. Daniel Myran, lead author of the study.
The number of individuals requiring hospital care for a CUD increased by 270% after the legalization of non-medical cannabis. Since before legalization to after, the percentage of all new cases of schizophrenia in Ontario who had received hospital care for a CUD before their schizophrenia diagnosis increased from 7% to 16%.
“Our study highlights the growing public health challenge posed by the combination of increasingly high-potency cannabis and rising regular cannabis use,” says Dr. Myran.
The study has been published in JAMA Network Open
On CUD generally and in relation to medical marijuana in the USA, a study out of the University of Kentucky last year found states with legalized medical cannabis saw a 42.7% increase in CUD compared to states that hadn’t yet done so.
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