Cannabis use is linked to brain changes in young adults at risk for psychosis

Young adults at risk for psychosis have reduced brain connectivity, a deficit that appears to be exacerbated by cannabis use, a new study suggests. The discovery paves the way for psychosis treatments that target symptoms that current drugs miss.

In the first study of its kind, McGill University researchers found a marked reduction in synaptic density—the connections between neurons that allow the brain to communicate—in people at risk of psychosis, compared to a healthy control group.

Not every cannabis user will develop psychosis, but for some, the risks are high. Our research helps clarify why. “Cannabis appears to disrupt the brain’s natural process of clearing and pruning synapses, which is essential for healthy brain development.”

Dr. Romina Mizrahi, senior author of the study and professor in McGill’s Department of Psychiatry

Hope for new treatments

Using advanced brain scanning technology, the team studied 49 participants aged 16 to 30, including people with recent psychotic symptoms and those at high risk. The results, published in JAMA Psychiatry, show that lower synaptic density is linked to social withdrawal and lack of motivation, symptoms that researchers say are difficult to treat.

“Current medications largely target hallucinations, but do not address symptoms that make it difficult to manage social relationships, work or school,” said first author Belen Blasco, a doctoral student in McGill’s Integrated Program in Neuroscience. “By focusing on synaptic density, we may ultimately develop treatments that enhance social functioning and quality of life for those affected.”

While cannabis is a known risk factor for developing psychosis, which can progress to schizophrenia, this is the first time researchers have measured structural changes in the brain of a high-risk population in real time.

The team’s next phase of research will investigate whether these observed brain changes could predict the development of psychosis, potentially allowing for earlier intervention.

The study was conducted at the Douglas Mental Health University Institute and the McGill University Neurological Institute-Hospital in Montreal. Supported by the Canadian Institutes of Health Research.