Cannabis use is rising globally with legalization and changing attitudes, but new research warns of serious effects on the brain—especially in young people at risk of psychosis.

A **McGill University study**, published in *JAMA Psychiatry*, found that cannabis reduces **synaptic density**, disrupting brain connectivity in individuals vulnerable to psychosis. “*Cannabis appears to disrupt the brain’s natural process of refining and pruning synapses,*” said Dr. Romina Mizrahi. This process is essential for healthy brain development.

The study, using brain scans of 49 participants aged 16–30, showed that cannabis worsens existing vulnerabilities. Affected brain areas include the **prefrontal cortex and striatum**, linked to thinking, emotions, and motivation. “*By focusing on synaptic density, we may eventually develop therapies that enhance social function,*” added researcher Belen Blasco.

Another **JAMA Network Open** study with over 1,000 adults found that heavy cannabis users had weaker brain activity in regions tied to **working memory and decision-making**. “*As cannabis use grows, studying its effects has become increasingly important,*” said lead author Joshua Gowin.

Cannabis also disturbs communication between brain networks. Even **CBD** didn’t protect against these effects—and sometimes made them worse. These findings urge a more cautious, informed approach to cannabis use.