Non-psychotic mental disorders are burdensome conditions within the general population, and their course is often complicated by the use of psychoactive substances and comorbid substance use disorders. Decriminalization or legalization of cannabis has led to concern that increasing use of cannabis will contribute to an increased burden of these disorders. In keeping with this concern, a sizable literature has established the existence of cross-sectional associations between cannabis use and non-psychotic mental disorders. However, few longitudinal studies have been conducted, and those that have been published have reported heterogeneous results. The potential advantages of longitudinal data for causal inference have not yet been realized in this literature. Questions remain about the temporality of the reported associations and the extent to which they are confounded by other variables. Consequently, there is insufficient evidence to confirm a causal role for cannabis in the etiology of non-psychotic mental disorders. There is also a stark contrast between survey data exploring subjective motivations for 'medical' cannabis use and the empirical literature about its potential efficacy for the treatment of non-psychotic disorders. Despite these limitations, the association of cannabis use with non-psychotic disorders, which has been strongly established by cross-sectional studies, has important implications for clinical practice and for guiding health services administration and policy.