Brain scans show similar abnormalities in schizophrenia patients whether or not they used cannabis

Both schizophrenia patients with cannabis use (n=227) and without (n=238) showed reduced whole brain, total grey matter, and hippocampal volumes compared to healthy controls (n=366). Direct comparison between the two patient groups showed no statistically significant differences, though grey matter deficits were more prominent in cannabis users.

Systematic search identified 10 MRI studies comparing brain volumes in first-episode schizophrenia patients with and without cannabis use and healthy controls. Meta-analysis pooled data from up to 5 independent studies for direct patient group comparisons.

Whether cannabis-associated psychosis represents a distinct brain disorder or the same disease with an additional risk factor has clinical implications for treatment and prognosis. These findings suggest substantial neurobiological overlap.

The overlap in brain abnormalities suggests cannabis-associated and non-cannabis schizophrenia may share core neuropathology rather than being fundamentally different diseases. However, the trend toward greater grey matter loss in cannabis users leaves open the possibility that cannabis adds insult to an already vulnerable brain.

Small number of studies (up to 5 for direct comparisons). Cross-sectional MRI cannot determine whether brain differences preceded cannabis use. Limited to first-episode patients, so long-term trajectories are unknown. Publication bias possible.