Areas With More Teen Cannabis Use Had Higher Rates of First Psychotic Episodes | Research

The takeaway

In an Italian region, area-level frequent cannabis use among 15-19 year-olds was associated with higher first-episode psychosis incidence and longer delays before treatment, alongside educational deprivation and population density.

Psychiatrists, public health planners, cannabis policy researchers, early psychosis intervention teams

12.9 months longer untreated psychosis in areas with more cannabis use

What the researchers found

Frequent cannabis use among teens (area-level) was associated with increased first-episode psychosis incidence (IRR=1.31). Cannabis use also increased the duration of untreated psychosis by an average of 12.9 months. Educational deprivation (IRR=1.15) and population density (IRR=1.14) also independently predicted FEP incidence.

Why it matters

This study goes beyond individual-level associations to show that community-level cannabis availability affects psychosis rates. The finding that cannabis delays treatment-seeking is particularly concerning for outcomes.

The numbers in context

1,240 FEP cases across 331 municipalities. Cannabis use IRR for FEP: 1.31 (95% CrI: 0.98-1.82). Cannabis increased DUP by 12.9 months. Educational deprivation IRR: 1.15. Population density IRR: 1.14.

How the study worked

Prospective analysis of 1,240 individuals aged 18-35 with first-episode psychosis from an early detection program in Emilia-Romagna, Italy. Area-level exposures from 331 municipalities were modeled using Bayesian hierarchical models informed by a directed acyclic graph for causal assumptions.

What this study cannot tell us

Area-level cannabis use is a proxy that may not reflect individual exposure. The cannabis IRR confidence interval crossed 1.0 (0.98-1.82). Italian setting may not generalize. Ecological study cannot prove individual-level causation.

How to read the evidence

Moderate: prospective population-based study with sophisticated Bayesian modeling, but ecological exposure measurement and borderline significance for the cannabis-incidence association

When this study was published

Published in 2025

The bigger picture

Community-level factors like cannabis availability, educational environment, and urbanicity all independently influence psychosis risk. This ecological perspective suggests that population-level interventions targeting multiple factors could reduce psychosis incidence.

Questions still open

Would reducing teen cannabis access at the community level decrease FEP incidence? Why does cannabis availability delay treatment-seeking? How do these area-level factors interact?

Common questions

Does community cannabis use affect psychosis rates?

This study found that areas with higher rates of frequent cannabis use among 15-19 year-olds had higher first-episode psychosis incidence, though the confidence interval was borderline (0.98-1.82). More clearly, higher cannabis use areas had significantly longer delays before psychosis treatment.

What other community factors affected psychosis risk?

Educational deprivation and population density also independently predicted higher psychosis incidence. The study used a causal modeling approach to disentangle these overlapping community-level influences.

Read the original research

The impact of socioeconomic factors on the incidence and characteristics of first-episode psychosis.

Epidemiology and psychiatric sciences, 34, e45

View on PubMed ↗Publisher’s paper ↗

Citation

Belvederi Murri, Martino; Onofrio, Alice; Punzi, Chiara; Caranci, Nicola; Rubolino, Enrico; Giovinazzi, Francesco; Azzolina, Danila; Folesani, Federica; Grassi, Luigi; Tarricone, Ilaria; Starace, Fabrizio. (2025). The impact of socioeconomic factors on the incidence and characteristics of first-episode psychosis.. Epidemiology and psychiatric sciences, 34, e45. https://doi.org/10.1017/S2045796025100206