Cannabis Effects on Brain Structure in Schizophrenia Remain Unclear Despite Extensive Imaging Research | Research

The takeaway

A systematic review of neuroimaging studies found inconclusive evidence for whether cannabis abuse alters brain morphology in schizophrenia, with no convincing evidence of structural changes before the onset of illness.

Read this if you are interested in whether cannabis structurally changes the brain in people with or at risk for schizophrenia.

No convincing evidence of brain structural changes before schizophrenia onset

What the researchers found

The review examined MRI studies comparing schizophrenia patients with and without cannabis abuse, as well as high-risk individuals. While some evidence suggested chronic cannabis abuse could alter brain morphology in patients who continued using cannabis, results were inconsistent across studies.

Critically, there was no convincing evidence that cannabis-related brain changes preceded schizophrenia onset when examining first-episode patients. Some weak evidence suggested cannabis might affect brain structures in high-risk subjects (those at elevated risk for psychosis), but these findings required replication.

Why it matters

Whether cannabis structurally changes the brain in ways that contribute to schizophrenia is a central question in the cannabis-psychosis debate. The finding that structural changes were not convincingly present before onset suggests cannabis may not cause the brain changes seen in schizophrenia, though it may modify them after illness onset.

The numbers in context

Systematic review of structural MRI studies. Inconclusive results across studies. No convincing evidence of pre-onset structural changes in first-episode patients. Weak evidence for high-risk subject brain effects needing replication.

How the study worked

Systematic review of structural MRI studies comparing high-risk and schizophrenia patients with and without cannabis abuse. Focused on brain morphological differences attributable to cannabis use in the context of psychosis.

What this study cannot tell us

Most included studies were cross-sectional, limiting causal inference. Cannabis use was typically self-reported and varied widely in amount and duration. Different brain regions and measurement methods across studies made comparison difficult. Publication bias may have influenced available literature.

How to read the evidence

Systematic review with inconclusive findings; moderate review methodology but weak underlying evidence.

When this study was published

Published in 2013. Neuroimaging studies of cannabis and psychosis have continued with larger samples and longitudinal designs.

The bigger picture

This review highlights the difficulty of disentangling cannabis effects from schizophrenia effects on the brain. Both cannabis and schizophrenia independently affect brain structure, making it challenging to attribute specific changes to one versus the other, especially in studies without baseline scans.

Questions still open

Would longitudinal neuroimaging studies that follow cannabis-using youth before and after psychosis onset clarify the relationship? Do specific brain regions show more consistent cannabis effects in schizophrenia? Does cannabis type (high-THC vs. balanced) matter for brain structural effects?

Common questions

Does cannabis damage the brain in schizophrenia?

This systematic review found the answer is not clear. Some studies suggested ongoing cannabis use might alter brain structure in schizophrenia patients, but results were inconsistent. Importantly, there was no convincing evidence that cannabis caused brain changes before schizophrenia developed, suggesting cannabis may not be the primary cause of the structural abnormalities seen in the illness.

Why is this question so hard to answer?

Both cannabis use and schizophrenia independently affect brain structure, making it very difficult to separate their effects. Most studies are cross-sectional (single snapshot in time), cannabis use histories are self-reported and variable, and different studies measure different brain regions with different methods. Longitudinal studies following people over time are needed but are expensive and complex.

Read the original research

Cannabis abuse and brain morphology in schizophrenia: a review of the available evidence.

European archives of psychiatry and clinical neuroscience, 263(1), 3-13

View on PubMed ↗Publisher’s paper ↗

Citation

Malchow, Berend; Hasan, Alkomiet; Fusar-Poli, Paolo; Schmitt, Andrea; Falkai, Peter; Wobrock, Thomas. (2013). Cannabis abuse and brain morphology in schizophrenia: a review of the available evidence.. European archives of psychiatry and clinical neuroscience, 263(1), 3-13. https://doi.org/10.1007/s00406-012-0346-3