Daily use of high-potency cannabis carried a 5-fold increased risk of psychotic disorder regardless of genetic predisposition to schizophrenia, and genetic risk did not predict heavy cannabis use, challenging the idea that genetics alone explain the cannabis-psychosis link.
Cannabis users of high-potency products, psychiatrists, genetics researchers, cannabis policy makers
OR 5.09 for daily high-potency use
What the researchers found
In the EU-GEI study, daily use of high-potency cannabis had OR 5.09 (95% CI 3.08-8.43) for psychotic disorder even after adjusting for schizophrenia polygenic risk score (PRS). Schizophrenia PRS was not associated with cannabis use patterns in cases or controls. No interaction between PRS and cannabis use was found.
Why it matters
A common counterargument to the cannabis-psychosis link is that shared genetics explain both. This study found that genetic predisposition to schizophrenia did not predict heavy cannabis use, and high-potency cannabis was a strong independent risk factor.
The numbers in context
EU-GEI: 1,098 participants. UK Biobank: 143,600 participants. Daily high-potency cannabis adjusted OR: 5.09 (95% CI 3.08-8.43, p=3.21x10^-10). No significant PRS x cannabis use interaction.
How the study worked
Two datasets: EU-GEI case-control study (1,098 participants) and UK Biobank (143,600 participants). Schizophrenia and cannabis use disorder polygenic risk scores calculated from GWAS data. Cannabis use patterns assessed and interaction with PRS tested.
What this study cannot tell us
Observational design cannot prove causation despite controlling for genetic confounding. Cannabis potency was self-reported. PRS captures only a fraction of genetic risk for schizophrenia. Different assessment methods across the two datasets.
How to read the evidence
Two large-scale datasets with genetic controls provide strong evidence, though observational design cannot fully establish causation.
When this study was published
2024 analysis of EU-GEI and UK Biobank data
The bigger picture
These findings from two large datasets strengthen the case that high-potency cannabis is an independent environmental risk factor for psychosis. As cannabis potency continues to rise globally, this has direct public health implications.
Questions still open
- Would reducing available cannabis potency decrease population-level psychosis rates? Is there a potency threshold below which psychosis risk is minimal? Do these findings apply to newer, extremely high-potency concentrates?
Common questions
Does genetic predisposition to schizophrenia make people use more cannabis?
How much does high-potency cannabis increase psychosis risk?
Read the original research
The impact of schizophrenia genetic load and heavy cannabis use on the risk of psychotic disorder in the EU-GEI case-control and UK Biobank studies.
Psychological medicine, 54(15), 1-13
Citation
Austin-Zimmerman, Isabelle; Spinazzola, Edoardo; Quattrone, Diego; Wu-Choi, Beatrice; Trotta, Giulia; Li, Zhikun; Johnson, Emma; Richards, Alexander L; Freeman, Tom P; Tripoli, Giada; Gayer-Anderson, Charlotte; Rodriguez, Victoria; Jongsma, Hannah E; Ferraro, Laura; La Cascia, Caterina; Tosato, Sarah; Tarricone, Ilaria; Berardi, Domenico; Bonora, Elena; Seri, Marco; D'Andrea, Giuseppe; Szöke, Andrei; Arango, Celso; Bobes, Julio; Sanjuán, Julio; Santos, Jose Luis; Arrojo, Manuel; Velthorst, Eva; Bernardo, Miguel; Del-Ben, Cristina Marta; Rossi Menezes, Paulo; Selten, Jean-Paul; Jones, Peter B; Kirkbride, James B; Rutten, Bart P F; Tortelli, Andrea; Llorca, Pierre-Michel; de Haan, Lieuwe; Stilo, Simona; La Barbera, Daniele; Lasalvia, Antonio; Schurnhoff, Franck; Pignon, Baptiste; van Os, Jim; Lynskey, Michael; Morgan, Craig; O' Donovan, Michael; Lewis, Cathryn M; Sham, Pak C; Murray, Robin M; Vassos, Evangelos; Di Forti, Marta. (2024). The impact of schizophrenia genetic load and heavy cannabis use on the risk of psychotic disorder in the EU-GEI case-control and UK Biobank studies.. Psychological medicine, 54(15), 1-13. https://doi.org/10.1017/S0033291724002058
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