An extensive body of evidence suggests that cannabis use in adolescence increases the risk of adult psychotic disorders (Arseneault et al., 2002, Moore et al., 2007, Rossler et al., 2012); based on Mendelian randomization studies it appears that this association may at least partly be causal (Gage et al., 2017, Vaucher et al., 2018). However, it is less clear whether adolescent cannabis use also predicts depression and other affective disorders (Moore et al., 2007). For instance, a recent 35-year longitudinal cohort study of male conscripts found a weak association between cannabis use and an increased risk for depression, but this association disappeared after adjustment for covariates (Manrique-Garcia et al., 2012).

Another prospective population-based study over 3 years including both male and female adults likewise found that cannabis use at baseline weakly increased the risk of depression and anxiety, but once again these associations disappeared after controlling for covariates (comprising alcohol and drug use, education level, and family climate) (Danielsson et al., 2016). In contrast, a longitudinal cohort study of 14-15 year-old students followed over seven years reported a remarkably strong association between early cannabis use and later depression and anxiety that persisted after adjustment for baseline covariates (Patton et al., 2002). Finally, a recent meta-analysis of longitudinal studies found that adolescent cannabis use predicts the development of depression (OR = 1.4), suicidal ideation (OR = 1.5) and suicide attempts (OR = 3.5), but not anxiety (OR = 1.2), in young adulthood (Gobbi et al., 2019).

The aim of the present work was to re-address the association between adolescent cannabis use and later mood and anxiety disorders. We extended previous research by focusing separately on mood disorders, anxiety disorders and suicidality. Moreover, we did not only control for baseline covariates, such as family climate and socio-economic background, but also for concomitant abuse of both alcohol and illicit drugs (including both cannabis and other substances) across the participants’ adult lives. Finally, with a total observation period of 30 years, the present longitudinal study is much longer than most research conducted thus far.