Cannabis disrupts brain activity in young adults prone to psychosis

Young adults at risk for psychosis show reduced brain connectivity, a deficit that cannabis use appears to exacerbate, a new study shows. The breakthrough paves the way for psychosis treatments that target symptoms that current medications miss.

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

The research is published in the news JAMA Psychiatry.

“Not every cannabis user will develop psychosis, but for some the risks are high. Our research helps clarify why,” says Dr. Romina Mizrahi, senior author of the study and professor at McGill's Department of Psychiatry. “Cannabis appears to disrupt the natural process of refining and pruning synapses in the brain, which is essential for healthy brain development.”

Hope for new treatments

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

“Current medications largely target hallucinations, but they don't address the symptoms that make it difficult to manage social relationships, work or school,” says first author Belen Blasco, a Ph.D. student at McGill's Integrated Program in Neuroscience. “By focusing on synaptic density, we can ultimately develop therapies that improve social function and quality of life for those affected.”

Although 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 brains of an at-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, making earlier intervention possible.

The study was conducted at the Douglas Mental Health University Institute and the Montreal Neurological Institute-Hospital of McGill University.