Cannabis disrupts brain activity in young adults prone to psychosis

In the first study of its kind, McGill University researchers found a significant decrease in synaptic density (connections between neurons that enable brain communication) in individuals at risk of psychosis compared to a healthy control group.

The study’s senior author and professor in McGill’s Department of Psychiatry, Dr. “Not every marijuana user develops psychosis, but for some the risks are high. Our research helps explain why,” said Romina Mizrahi.

“Marijuana appears to disrupt the brain’s natural process of healing and pruning synapses, which is essential for healthy brain development.”

Hope for new treatments

Using advanced brain scanning technology, the team examined 49 participants aged 16 to 30, including people who had recent psychotic symptoms and were considered to be at high risk. The results were published on: JAMA Psychiatry, The findings show that low 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 they 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 can eventually develop therapies that improve social function and quality of life for those affected.”

While marijuana 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 brains of a high-risk population in real time.

The team’s next phase of research will investigate whether these observed brain changes can predict the development of psychosis and potentially enable earlier intervention.

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