People with Psychosis Report More Intense Reactions to Cannabis | Research

The takeaway

First-episode psychosis patients reported more frequent psychotic-like experiences during cannabis intoxication than controls, and this sensitivity increased with heavier use, suggesting a specific vulnerability.

Psychiatrists, psychosis researchers, harm reduction professionals

FEP patients showed dose-dependent increases in psychotic-like cannabis experiences that controls did not

What the researchers found

In the EU-GEI study across 15 sites and 6 countries, FEP patients (n=655) showed a steeper increase in psychotic-like intoxication experiences at higher cannabis use levels compared to controls (n=654), while euphoric experiences did not differ between groups.

Why it matters

The finding that psychosis patients have a specific vulnerability to cannabis-induced psychotic-like experiences, but not euphoric ones, suggests a biological mechanism rather than simply heavier use patterns.

The numbers in context

655 FEP patients; 654 controls; 15 sites across 6 countries; significant interaction for caseness x frequency of use for psychotic-like experiences (p<0.001) but not euphoric experiences (p>0.5).

How the study worked

Multi-site case-control analysis from the EU-GEI study (2010-2015) using multiple regression to model predictors of cannabis-induced psychotic-like and euphoric experiences across 15 sites in 6 countries.

What this study cannot tell us

Cross-sectional design cannot determine whether sensitivity preceded psychosis onset; retrospective self-report of intoxication experiences; potential recall bias in patient group.

How to read the evidence

Large multi-national case-control study with robust statistical methods, though limited by cross-sectional design and retrospective self-report.

When this study was published

Data from EU-GEI study collected 2010-2015.

The bigger picture

These findings suggest that people who develop psychosis may have a pre-existing or illness-related sensitivity to the psychotomimetic effects of cannabis that is dose-dependent and distinct from the drug's rewarding effects.

Questions still open

Could measuring psychotic-like cannabis experiences serve as an early warning sign for psychosis risk? Is this heightened sensitivity present before the first psychotic episode?

Common questions

Do people with psychosis get more paranoid from cannabis than others?

In this study, first-episode psychosis patients reported more frequent psychotic-like experiences during cannabis intoxication, and this gap widened with heavier use. However, euphoric experiences were similar between groups.

Does heavier cannabis use affect people with psychosis differently?

Yes. While both groups reported more psychotic-like experiences with heavier use, the increase was significantly steeper for psychosis patients, suggesting a specific dose-dependent vulnerability.

Read the original research

Association of extent of cannabis use and psychotic like intoxication experiences in a multi-national sample of first episode psychosis patients and controls.

Psychological medicine, 51(12), 2074-2082

View on PubMed ↗Publisher’s paper ↗

Citation

Sami, Musa; Quattrone, Diego; Ferraro, Laura; Tripoli, Giada; Cascia, Erika La; Gayer-Anderson, Charlotte; Selten, Jean-Paul; Arango, Celso; Bernardo, Miguel; Tarricone, Ilaria; Tortelli, Andrea; Gatto, Giusy; Del Peschio, Simona; Del-Ben, Cristina Marta; Rutten, Bart P; Jones, Peter B; van Os, Jim; de Haan, Lieuwe; Morgan, Craig; Lewis, Cathryn; Bhattacharyya, Sagnik; Freeman, Tom P; Lynskey, Michael; Murray, Robin M; Forti, Marta Di. (2021). Association of extent of cannabis use and psychotic like intoxication experiences in a multi-national sample of first episode psychosis patients and controls.. Psychological medicine, 51(12), 2074-2082. https://doi.org/10.1017/S0033291720000847