Association between cannabis use and mental health disorders in adolescents in Catalonia: results of a cohort study

Background: Numerous studies show that cannabis use during adolescence is associated with an increased risk of developing cannabis related disorders. Cannabis use is associated with the use of other drugs, and with the development of psychotic disorders. In addition, age of onset of cannabis use is associated with moderate risk of the development of other mental health disorders (MHD).

In Catalonia, cannabis is the most consumed illicit substance and the one with the highest treatment demand among adolescents. The aim of this study is to find out the incidence of MHD among minors who requested treatment for cannabis use disorders.

Methods: A retrospective observational cohort study with an exposed cohort consisting of minors who requested treatment for cannabis use disorders between 2015 and 2019 (n=948) and who did not have MHD prior to the onset of cannabis use. The unexposed cohort was matched (1:5) for potential confounding variables.

A descriptive univariate analysis was performed and the incidence of developing MHD was calculated according to cannabis exposure. Finally, a conditional Poisson regression stratified by sex was performed to obtain the incidence rate ratios of MHD.

Results: In the exposed cohort, 77.4% were male, with a median age of 16.7 and a median age of onset of cannabis use of 14.0. 6.9% had lower socioeconomic status and 76.0% lived in urban or semi-urban areas.

The cumulative incidence of developing MHD was 19.6% in the exposed cohort and 3.1% in the matched cohort, representing 6.3 times higher relative risk of developing MHD among those exposed to cannabis; and the incidence rate ratio was found to be twice as high in women (14.0 vs. 6.9).

Conclusions: This study, in line with published literature, shows a higher risk of developing MHD (not only psychotic disorders), among those exposed to cannabis and this risk is greater among women.