International expert consensus finds converging evidence that cannabis increases psychosis risk, especially at higher doses and younger ages | Research

The takeaway

A WFSBP task force of international experts concluded that converging evidence supports cannabis as a component cause of psychosis, with greater risk at higher doses and earlier exposure, though cannabis alone is neither necessary nor sufficient to cause the disorder.

Psychiatrists, policymakers, cannabis users concerned about psychosis risk, and public health professionals.

Higher dose + younger age = greater psychosis risk (international consensus)

What the researchers found

Converging evidence supports that cannabis increases psychosis risk across a spectrum from transient states to chronic psychosis. The relationship shows dose-response (greater dose = greater risk) and age-response (earlier exposure = greater risk). Some causality criteria are met, but alternate explanations cannot be excluded. Cannabis negatively impacts the course of established psychosis. The endocannabinoid system is altered in psychotic disorders.

Why it matters

This represents the most authoritative expert consensus statement on cannabis and psychosis, from the World Federation of Societies of Biological Psychiatry, providing a balanced synthesis of evidence for clinical and policy guidance.

The numbers in context

Dose-response and age-response relationships documented. Cannabis affects both psychosis risk and the course of established psychotic disorders. Cannabis is described as one of "multiple causal components."

How the study worked

WFSBP task force consensus paper reviewing the literature on cannabis, cannabinoids, and psychosis, integrating epidemiological, clinical, and neurobiological evidence.

What this study cannot tell us

Consensus paper synthesizing existing evidence, not generating new data. Cannot conclusively exclude reverse causality or confounders. The "component cause" framework is inherently difficult to test definitively.

How to read the evidence

Expert consensus paper from WFSBP task force, integrating multiple lines of evidence.

When this study was published

Published in 2022.

The bigger picture

The nuanced conclusion that cannabis is a "component cause" but neither necessary nor sufficient represents a mature understanding that avoids both dismissing the risk and overstating cannabis as the sole cause of psychosis.

Questions still open

Can individual risk be quantified based on genetics and exposure patterns? Would CBD-dominant products carry lower psychosis risk? What proportion of psychosis cases could be prevented by eliminating cannabis exposure?

Common questions

Does cannabis cause psychosis?

International experts concluded that cannabis increases psychosis risk but is neither necessary nor sufficient to cause it alone. It is described as one component cause among many, with risk increasing with higher doses and earlier age of first use.

Does cannabis make existing psychosis worse?

Yes. The expert consensus found that in people with established psychosis, cannabis has a negative impact on both the course and expression of the illness, supporting clinical recommendations to avoid cannabis in this population.

Read the original research

Consensus paper of the WFSBP task force on cannabis, cannabinoids and psychosis.

The world journal of biological psychiatry : the official journal of the World Federation of Societies of Biological Psychiatry, 23(10), 719-742

View on PubMed ↗Publisher’s paper ↗

Citation

D'Souza, Deepak Cyril; DiForti, Marta; Ganesh, Suhas; George, Tony P; Hall, Wayne; Hjorthøj, Carsten; Howes, Oliver; Keshavan, Matcheri; Murray, Robin M; Nguyen, Timothy B; Pearlson, Godfrey D; Ranganathan, Mohini; Selloni, Alex; Solowij, Nadia; Spinazzola, Edoardo. (2022). Consensus paper of the WFSBP task force on cannabis, cannabinoids and psychosis.. The world journal of biological psychiatry : the official journal of the World Federation of Societies of Biological Psychiatry, 23(10), 719-742. https://doi.org/10.1080/15622975.2022.2038797