Among 89 people with first-episode psychosis, lifetime cannabis users showed no differences from non-users on verbal memory, verbal fluency, or attention, though cannabis users had more positive symptoms and non-users had more negative symptoms.
Psychiatrists treating first-episode psychosis, researchers studying cannabis and psychosis
No cognitive differences between cannabis users and non-users with first-episode psychosis
What the researchers found
Of 89 FEP patients, 61 (68.5%) were lifetime cannabis users. Cannabis users had significantly more positive psychotic symptoms, while non-users displayed more negative symptoms. There were no differences between groups on tests of verbal memory, verbal fluency, or attention.
Why it matters
The concern that cannabis compounds cognitive deficits in psychosis has treatment implications. This finding of no additive cognitive effect is reassuring but must be interpreted carefully.
The numbers in context
89 FEP patients; 61 (68.5%) lifetime cannabis users. Cannabis users: more positive symptoms. Non-users: more negative symptoms. No cognitive differences on any task.
How the study worked
Cross-sectional study of 89 people diagnosed with first-episode psychosis. Cannabis use defined as 3+ times/week for 4+ weeks. Cognitive battery assessed verbal memory, verbal fluency, and attention. Controlled for recency of use and other illicit substance use.
What this study cannot tell us
Cross-sectional; relatively small sample; lifetime use definition does not capture current exposure; limited cognitive battery (3 domains); cannot determine if pre-existing cognitive abilities differ.
How to read the evidence
Small cross-sectional study with limited cognitive measures in a first-episode psychosis population.
When this study was published
Published in 2020.
The bigger picture
This adds to a mixed literature on cannabis and cognition in psychosis. The symptom profile differences (more positive symptoms in users, more negative in non-users) may reflect different illness subtypes rather than direct cannabis effects.
Questions still open
- Do cannabis users and non-users with psychosis represent different illness subtypes? Would more sensitive cognitive measures detect differences?
Common questions
Does cannabis worsen thinking problems in psychosis?
Why did cannabis users have different symptoms?
Read the original research
The relationship between cannabis use and cognition in people diagnosed with first-episode psychosis.
Psychiatry research, 293, 113424
Citation
de Vos, Chloé; Leopold, Karolina; Blanke, Elisabeth S; Siebert, Stefan; Baumgardt, Johanna; Burkhardt, Eva; Bechdolf, Andreas. (2020). The relationship between cannabis use and cognition in people diagnosed with first-episode psychosis.. Psychiatry research, 293, 113424. https://doi.org/10.1016/j.psychres.2020.113424
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