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

The takeaway

A meta-analysis of 10 MRI studies found that schizophrenia patients with and without cannabis use histories showed overlapping patterns of brain volume reductions, though grey matter deficits trended larger in cannabis users.

Psychiatrists, neuroimaging researchers, psychosis specialists

No significant brain volume differences between cannabis-using and non-using schizophrenia patients

What the researchers found

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.

Why it matters

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 numbers in context

10 MRI studies; 227 schizophrenia patients with cannabis use; 238 without; 366 healthy controls; up to 5 studies available for direct comparison; both groups showed reduced whole brain, grey matter, and hippocampal volumes vs. controls

How the study worked

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.

What this study cannot tell us

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.

How to read the evidence

Meta-analysis of structural MRI studies with appropriate methodology, but limited by small number of available studies for direct comparison.

When this study was published

Published in 2021.

The bigger picture

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.

Questions still open

Would longitudinal studies reveal diverging brain trajectories between cannabis-using and non-using schizophrenia patients over time? Does the trend toward greater grey matter loss in cannabis users become significant with larger samples?

Common questions

Are the brain changes in cannabis-associated schizophrenia different?

Not significantly. Both groups showed reduced whole brain volume, total grey matter, and hippocampal volume compared to healthy controls. While cannabis users trended toward greater grey matter loss, the difference was not statistically significant.

Does this mean cannabis does not affect the brain in psychosis?

Not necessarily. The overlap in brain structure does not rule out that cannabis contributes additional risk or worsens outcomes through other mechanisms not captured by volumetric MRI.

Read the original research

Are Schizophrenic disorders with or without early cannabis use neurobiologically distinct disease entities? A meta-analysis of magnetic resonance imaging studies.

Psychiatry research, 297, 113731

View on PubMed ↗Publisher’s paper ↗

Citation

De Peri, Luca; Traber, Rafael; Bolla, Emilio; Vita, Antonio. (2021). Are Schizophrenic disorders with or without early cannabis use neurobiologically distinct disease entities? A meta-analysis of magnetic resonance imaging studies.. Psychiatry research, 297, 113731. https://doi.org/10.1016/j.psychres.2021.113731