Cannabis Users With Psychosis Show Fewer Cognitive Biases Than Non-Users

What the researchers found

Daily and occasional cannabis use were associated with lower odds of speech illusions (OR = 0.605 and 0.646) and jumping to conclusions bias (OR = 0.625 and 0.602) compared to never-use. Low-potency use was associated with higher odds of all three cognitive biases compared to high-potency use.

Why it matters

The counterintuitive finding that cannabis users show fewer cognitive biases challenges simple narratives about cannabis and cognition in psychosis.

The numbers in context

1,914 participants; daily use OR 0.605 for speech illusions; occasional use OR 0.602 for JTC; low vs high potency: OR 1.829 for SI, 1.393 for FRP, 1.661 for JTC.

How the study worked

Cross-sectional analysis of 543 first-episode psychosis patients, 203 siblings, and 1,168 controls from the EU-GEI multi-site study.

What this study cannot tell us

Cross-sectional design prevents causal inference. Self-reported cannabis potency.

How to read the evidence

Large multi-site study with appropriate controls, limited by cross-sectional design and self-reported potency.

When this study was published

2024 publication

The bigger picture

These findings complicate the cannabis-psychosis narrative and raise questions about self-selection and the role of the endocannabinoid system in cognitive processing.

Questions still open

• Why would cannabis users show fewer cognitive biases than non-users?
• Is the low-potency finding a real effect or artifact of who chooses low-potency products?

Common questions

Read the original research

Cannabis use and cognitive biases in people with first-episode psychosis and their siblings.

Psychological medicine, 54(15), 1-11

Citation

Roldan, L; Sánchez-Gutiérrez, T; Fernández-Arias, I; Rodríguez-Toscano, E; López, G; Merchán-Naranjo, J; Calvo, A; Rapado-Castro, M; Parellada, M; Moreno, C; Ferraro, L; La Barbera, D; La Cascia, C; Tripoli, G; Di Forti, M; Murray, R M; Quattrone, D; Morgan, C; Gayer-Anderson, C; Jones, P B; Jongsma, H E; Kirkbride, J B; van Os, J; García-Portilla, P; Al-Halabí, S; Bobes, J; de Haan, L; Bernardo, M; Santos, J L; Sanjuán, J; Arrojo, M; Szoke, A; Rutten, B P; Stilo, S A; Tarricone, I; Lasalvia, A; Tosato, S; Llorca, P-M; Menezes, P Rossi; Selten, J-P; Tortelli, A; Velthorst, E; Del-Ben, C M; Arango, C; Díaz-Caneja, C M. (2024). Cannabis use and cognitive biases in people with first-episode psychosis and their siblings.. Psychological medicine, 54(15), 1-11. https://doi.org/10.1017/S0033291724001715

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