The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multi-centre case-control study

The Lancet Psychiatry

This study published in Lancet Psychiatry in March 2019 suggests that daily cannabis users had more than three-fold higher odds for incidence of psychosis as compared to non-users. In regions where THC concentration are often greater than 10% (high-potency), the odds for a psychotic episode were five times greater in daily cannabis users compared to non-users. In regions with lower potency cannabis, the odds were just over two.

The study recruited 901 patients (ages 18 – 64) between mid-2010 and mid-2015 that were diagnosed with first-episode psychosis at ten sites in Europe and one in Brazil. They were compared with more than 1200 healthy individuals from across the same areas. Users were asked about the age when they started using cannabis, frequency of cannabis use, and how much they spent on it.

The analysis accounted for differences in demographics, socioeconomic variables, and use of other drugs. Thus, the findings suggest that daily cannabis use—and the use of high-potency cannabis in particular—can lead to a first-time psychotic episode. The researchers estimate that if high potency cannabis were no longer available, incidences of first-episode psychosis would decrease by 12%. 

Given the changing legal status of cannabis use across the world, these findings highlight the risk of frequent use of high-potency cannabis.

For the original article, click here.

Di Forti, M. et al. (2019). The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multi-centre case-control study. The Lancet Study, Volume 6 (Issue 5), pp. 427-436. DOI: https://doi.org/10.1016/S2215-0366(19)30048-3