A recent study from McGill University has shown how cannabis use may negatively affect brain development, especially in young adults at risk of psychosis. Researchers found that marijuana can “reduce brain connectivity” by lowering synaptic density — the links between neurons that help the brain communicate.

The study, published in JAMA Psychiatry, used advanced brain scans on 49 participants aged 16 to 30, including those with recent psychotic symptoms or high risk of psychosis.

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

First author Belen Blasco noted, “Current medications largely target hallucinations… By focusing on synaptic density, we may eventually develop therapies that enhance social function and quality of life.”

Researchers now plan to study whether these brain changes can predict psychosis, aiming for earlier diagnosis and better treatment options.