First-episode schizophrenia patients who used cannabis performed better on cognitive tests | Research

The takeaway

Among patients with first-episode schizophrenia, those with a history of cannabis use showed less cognitive impairment than non-users, particularly in visual memory.

Researchers studying the relationship between cannabis and psychosis, and clinicians treating early psychosis.

Cannabis-using patients showed superior visual memory scores

What the researchers found

First-episode schizophrenia patients with lifetime cannabis use (n=30) showed better cognitive performance than non-using patients (n=53), with the most prominent difference in visual memory. The two patient groups did not differ in symptom severity or medication. Among healthy controls, cannabis use made no cognitive difference.

Why it matters

The finding that cannabis-using schizophrenia patients performed better cognitively challenges the assumption that cannabis worsens cognitive outcomes in psychosis. This pattern is consistent with the "dual pathway" hypothesis, where cannabis-related psychosis may require lower genetic vulnerability.

The numbers in context

30 first-episode schizophrenia cannabis users, 53 schizophrenia non-users, 20 healthy control users, 49 healthy control non-users. Cannabis-using patients showed superior visual memory compared to non-using patients.

How the study worked

Case-control study comparing cognitive test performance across four groups: first-episode schizophrenia patients who used cannabis (n=30), schizophrenia patients who did not (n=53), healthy controls who used cannabis (n=20), and healthy controls who did not (n=49). All underwent extensive neurocognitive assessment.

What this study cannot tell us

Small sample sizes. Cross-sectional design cannot determine causation. Lifetime cannabis use measured by questionnaire. Cannot distinguish between cannabis as cause vs. marker of different illness pathways.

How to read the evidence

Small sample sizes and cross-sectional design. Findings are consistent with prior research but cannot establish causation.

When this study was published

2021 study from a Czech clinical sample.

The bigger picture

This finding does not mean cannabis protects cognition in schizophrenia. One leading interpretation is that people who develop psychosis through cannabis exposure may have needed less underlying genetic vulnerability, meaning they started from a higher cognitive baseline.

Questions still open

Does cannabis-related psychosis represent a distinct subtype with different cognitive profiles? Would these cognitive advantages persist over time? Is the finding driven by pre-existing differences rather than cannabis effects?

Common questions

Does this mean cannabis is protective for cognition in schizophrenia?

Not necessarily. The more likely explanation is that people who develop psychosis partly through cannabis use may have had less underlying genetic vulnerability, meaning they started with higher cognitive ability.

Did cannabis use affect symptom severity?

No. Cannabis-using and non-using schizophrenia patients did not differ in general psychopathology, positive symptoms, negative symptoms, or medication use.

Read the original research

Cognitive performance and lifetime cannabis use in patients with first-episode schizophrenia spectrum disorder.

Cognitive neuropsychiatry, 26(4), 257-272

View on PubMed ↗Publisher’s paper ↗

Citation

Hájková, M; Knížková, K; Siroňová, A; Keřková, B; Jonáš, J; Šustová, P; Dorazilová, A; Rodriguez, M. (2021). Cognitive performance and lifetime cannabis use in patients with first-episode schizophrenia spectrum disorder.. Cognitive neuropsychiatry, 26(4), 257-272. https://doi.org/10.1080/13546805.2021.1924649