Psychotic patients who used cannabis as teens had less brain damage than those who did not | Research

The takeaway

In a counterintuitive finding, people with psychosis who had used cannabis during adolescence showed less gray matter loss than psychotic patients who had not used cannabis, with brain structure similar to healthy controls.

Read this if you want to understand the complex relationship between adolescent cannabis use, brain structure, and psychosis.

Cannabis-using psychosis patients had brain structure similar to healthy controls

What the researchers found

Researchers examined brain structure in 109 people with psychotic disorders, comparing those with and without a history of adolescent cannabis use. Both groups showed lower total and regional gray matter density compared to healthy controls, as expected in psychotic disorders.

However, the group with adolescent cannabis use showed significantly less gray matter reduction than the non-using psychosis group. This was especially pronounced in schizophrenia patients, where non-users showed extensive gray matter loss in frontal, temporal, parietal, and subcortical regions, while users with adolescent cannabis history did not differ significantly from healthy controls in brain structure.

This suggests that psychosis with a history of adolescent cannabis use may represent a distinct subtype, potentially driven by different etiological factors. Those who develop psychosis through the cannabis pathway may not need as much underlying brain pathology to become ill.

Why it matters

This finding challenges the simple narrative that cannabis damages the brain and causes psychosis. Instead, it suggests that cannabis-associated psychosis may represent a different pathway to illness, one that requires less pre-existing brain pathology. People who develop psychosis through the cannabis route may have fundamentally different neurobiology than those who develop it without cannabis involvement.

The numbers in context

109 psychotic patients analyzed. Both cannabis-using and non-using psychosis groups had lower gray matter density than controls. Cannabis-using psychosis group showed attenuated (less severe) gray matter reductions. Schizophrenia patients without cannabis history showed robust gray matter loss in fronto-temporal, parietal, and subcortical regions. Cannabis-using psychosis patients did not differ significantly from healthy controls in brain structure.

How the study worked

This was a cross-sectional neuroimaging study using voxel-based morphometry to measure gray matter density in 109 people with psychotic disorders (schizophrenia and bipolar I) and healthy controls. Participants were stratified by history of adolescent cannabis use. Regional and total gray matter density estimates were compared across groups.

What this study cannot tell us

The cross-sectional design cannot determine whether the brain structure differences existed before psychosis onset. Sample sizes within subgroups were relatively small. The study relied on self-reported cannabis use history. There may be other confounding factors that differ between cannabis-using and non-using psychosis patients. Gray matter density is only one measure of brain structure and function.

How to read the evidence

This is a moderately-sized neuroimaging study with appropriate methods, but the cross-sectional design and subgroup analyses limit definitive conclusions.

When this study was published

Published in 2018. The concept of psychosis subtypes based on cannabis exposure history continues to be explored.

The bigger picture

This study supports the idea that psychotic disorders are heterogeneous, with multiple pathways leading to similar clinical presentations. The cannabis-associated pathway may involve more environmental triggering and less neurodevelopmental brain pathology. This has implications for treatment approaches, prognosis, and our fundamental understanding of what psychosis is.

Questions still open

Do people with cannabis-associated psychosis have better treatment response or prognosis due to less underlying brain pathology? What alternative mechanisms, beyond structural brain changes, drive psychosis in cannabis users? Could this finding inform personalized treatment approaches in psychotic disorders?

Common questions

Does this mean cannabis protects the brain?

No. The study found that people who developed psychosis after adolescent cannabis use had less structural brain damage than those who developed psychosis without cannabis. This likely means cannabis-associated psychosis takes a different pathway, not that cannabis is protective.

What does this mean for the idea that cannabis causes psychosis?

It suggests the relationship is more nuanced than simple causation. Cannabis may trigger psychosis in some individuals who would not have become psychotic otherwise, potentially through mechanisms that do not require extensive brain structural changes.

Read the original research

Associations between adolescent cannabis use and brain structure in psychosis.

Psychiatry research. Neuroimaging, 276, 53-64

View on PubMed ↗Publisher’s paper ↗

Citation

Abush, Hila; Ghose, Subroto; Van Enkevort, Erin A; Clementz, Brett A; Pearlson, Godfrey D; Sweeney, John A; Keshavan, Matcheri S; Tamminga, Carol A; Ivleva, Elena I. (2018). Associations between adolescent cannabis use and brain structure in psychosis.. Psychiatry research. Neuroimaging, 276, 53-64. https://doi.org/10.1016/j.pscychresns.2018.03.008