A new study has shown clear evidence of the connection between cannabis (marijuana, “weed”) use and risk of developing schizophrenia or a related psychotic illness.
The research team examined the health information for over 13 million Ontarians aged 14 to 65 years who had never been diagnosed with schizophrenia before the study started. Over the 17 years from 2006 to 2022, a time of changing marijuana legalization policies, they found that new cases of schizophrenia that were associated with marijuana use nearly tripled. New cases of other psychotic illnesses also accelerated over this time. There were 5 times more people coming to hospital with cannabis use disorders than in 2006.
A cannabis use disorder (CUD) is when a person keeps using cannabis even though it is causing health and other problems in their lives.
A related study reported that there is also a markedly increased risk of dying for individuals with cannabis use disorder.
We have previously highlighted another Ontario study showing that Emergency Department visits for cannabis use were related to a later healthcare visit for an anxiety disorder.
Our Clinic team continues to advise our patients not to use cannabis - smoking or vaping or edibles because of high potential risks in terms of worsening learning difficulties, heart conditions, anxiety, and developing schizophrenia. There are also GI side effects (e.g., abdominal pain, nausea, vomiting) that can be severe. If you have any concerns, please make an appointment to discuss them with your doctor.
References
Changes in Incident Schizophrenia Diagnoses Associated With Cannabis Use Disorder After Cannabis Legalization Myran DT, Pugliese M, Harrison LD, et al. JAMA Netw Open. 2025;8(2):e2457868. doi:10.1001/jamanetworkopen.2024.57868
See also
Schizophrenia cases linked to cannabis use disorders nearly tripled over 17-year period: Ontario study CTV News, February 4, 2025
Psychotic Disorders (includes schizophrenia) Health Conditions Explained, The International 22q11.2 Foundation
Psychiatry (Part of “Features in Adults with 22q11.2 Deletion Syndrome”) Recreational Drugs The Dalglish Family 22q Clinic
Understanding Your Risk for Cannabis Use Disorder US Centers for Disease Control and Prevention
Addiction to cannabis Health Canada