Young psychosis patients who used cannabis showed no cognitive advantage or disadvantage over non-users | Research

The takeaway

Among 103 young adults with psychosis, cannabis-using and non-using patients showed no significant cognitive differences at illness onset, though both groups performed worse than healthy controls across most measures.

Psychiatrists, early psychosis intervention researchers, and anyone studying the cannabis-psychosis relationship.

No cognitive difference at onset

What the researchers found

Healthy controls outperformed both patient groups across most cognitive measures, but no significant differences were found between cannabis-using (n=24) and cannabis-abstinent (n=79) psychosis patients on any cognitive measure, including premorbid intelligence, processing speed, flexibility, memory, attention, and visuospatial function.

Why it matters

Some research suggests former cannabis users with psychosis have better cognition than never-users, implying cannabis may precipitate psychosis in otherwise higher-functioning individuals. This study, conducted at illness onset rather than later, found no such difference.

The numbers in context

24 cannabis-using and 79 cannabis-naive psychosis patients, aged 16-25. Both groups impaired vs healthy controls. No significant differences between groups on premorbid IQ, psychomotor speed, mental flexibility, verbal learning/memory, verbal fluency, sustained attention, or visuospatial learning.

How the study worked

Cross-sectional comparison of 24 cannabis-using and 79 cannabis-naive psychosis patients aged 16-25, plus healthy controls. Comprehensive neurocognitive battery administered at or near illness onset.

What this study cannot tell us

Small cannabis-using group (n=24). Cross-sectional design at a single timepoint. Cannabis use was current, not historical, so acute effects may mask underlying differences. Cannot determine whether cannabis caused or merely preceded psychosis.

How to read the evidence

Rated moderate because the study has a reasonable sample and comprehensive cognitive battery, though the cannabis-using group is small.

When this study was published

Published in 2019.

The bigger picture

The absence of cognitive differences between cannabis-using and non-using psychosis patients at onset is consistent with the idea of an alternative pathway to psychosis through cannabis, where cannabis precipitates illness in individuals who might not otherwise have become ill.

Questions still open

Would cognitive differences emerge with longer follow-up? Does cannabis-precipitated psychosis have a different trajectory than non-cannabis psychosis? Could cognitive profiling distinguish cannabis-related from other psychosis pathways?

Common questions

Do cannabis-using psychosis patients think differently than non-users?

At the time of first illness, this study found no cognitive differences. Both groups performed worse than healthy controls, but cannabis users were not distinguishable from non-users on any test.

What does this mean about cannabis and psychosis?

The authors suggest some people develop psychosis regardless of cannabis use, while others may have their illness triggered by cannabis. The lack of cognitive differences at onset is consistent with cannabis opening an alternative pathway to psychosis.

Read the original research

The neuropsychological profiles of young psychosis patients with and without current cannabis use.

Cognitive neuropsychiatry, 24(1), 40-53

View on PubMed ↗Publisher’s paper ↗

Citation

Bogaty, Sophia E R; Crouse, Jacob J; Hickie, Ian B; Hermens, Daniel F. (2019). The neuropsychological profiles of young psychosis patients with and without current cannabis use.. Cognitive neuropsychiatry, 24(1), 40-53. https://doi.org/10.1080/13546805.2018.1562887