A McGill University-led study found that people with cannabis use disorder (CUD) had elevated dopamine levels in a brain region associated with psychosis.
“This could help explain why cannabis use increases the risk of hallucinations and delusions, key symptoms of schizophrenia and other psychotic disorders,” said first author Jessica Ahrens, a PhD student in McGill’s Integrated Program in Neuroscience.
Dopamine is a neurotransmitter that helps regulate mood and motivation, and an excess is associated with psychosis. While it was known that cannabis influences dopamine, this study clarifies where in the brain these changes occur. Cannabis use disorder is when someone has trouble controlling their cannabis use, continues despite negative effects, and may experience cravings or withdrawal.
“For a long time, clinical researchers across the world have been searching for a link showing that cannabis affects the brain mechanism behind psychosis. We now show that a shared dopamine pathway could be the answer,” Ahrens said.
The study involved 61 people, including those with and without cannabis use disorder, as well as individuals with early-stage schizophrenia, some of whom also had CUD. Using a specialized brain scan called neuromelanin-MRI, researchers at Western University measured their neuromelanin signal, which reflects dopamine activity.
People with CUD had an abnormally high neuromelanin signal, and the elevation was tied to the severity of their cannabis use. In contrast, those without schizophrenia or CUD did not show this increase. Larger studies are needed to confirm these findings.
Educating youth about cannabis risks
About one-in-five youth in Canada are cannabis users, consuming it daily or almost daily. Understanding the drug’s impact on mental health remains a pressing question.
“The lack of clear biological evidence linking cannabis to psychosis has made it harder to persuade young people with psychotic symptoms to reduce their use,” said Dr. Lena Palaniyappan, Professor of Psychiatry at McGill and Psychiatrist at the Douglas Mental Health University Institute.
“Our findings could help doctors and mental health professionals better educate patients about the potential risks of frequent cannabis use, especially for those with a family history of psychosis,” he said.
Future research will explore whether long-term cannabis use leads to lasting dopamine changes and whether these effects reverse after quitting.
About the study
“Convergence of Cannabis and Psychosis on the Dopamine System” by Jessica Ahrens, Clifford Cassidy, and Lena Palaniyappan et al., was published in Jama Psychiatry.
The study was supported by the Canadian Institutes of Health Research, the Schizophrenia Society of Canada Foundation, the Canadian Consortium for Early Intervention in Psychosis, the Fonds de Recherche du Québec — Santé, the Quebec Bio-Imaging Network, the Canada First Research Excellence Fund, the Canada Research Chairs program and the Canada Foundation for Innovation.