BackgroundAdolescence is characterised by psychological and neural development. Cannabis harms may be accentuated during adolescence. We hypothesised adolescents would be more vulnerable to cannabis-related mental health and addiction problems than adults.MethodAs part of the ‘CannTeen’ study, we conducted a cross-sectional analysis. There were 274 participants: adolescent users (n=76; 16-17 years old), and controls (n=63), and adult users (n=71; 26-29 years old), and controls (n=64). The users used cannabis 1-7 days/week and controls had 0-10 lifetime exposures to cannabis. We measured DSM-5 CUD, Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Psychotomimetic States Inventory-adapted (PSI-a). Linear and logistic regressions with age-group, user-group, their interaction, and pre-defined covariates were conducted.ResultsAfter adjustment for covariates, adolescent users were more likely to have severe CUD than adult users (OR=3.474, 95% CI=1.501-8.036). Users reported greater psychotic-like symptoms than controls (b=6.004, 95% CI=1.211-10.796) and adolescents reported greater psychotic-like symptoms than adults (b=5.509, 95% CI=1.070-9.947). Depression and anxiety were not associated with user-group. No significant interactions between age-group and user-group were identified. Exploratory analyses suggested that users with severe CUD had greater depression and anxiety than users without.ConclusionsAdolescent cannabis users are more likely than adult cannabis users to have severe CUD. Adolescent cannabis users have greater psychotic-like symptoms than adult cannabis users and adolescent controls, through an additive effect. There was no evidence of an amplified vulnerability to cannabis-related depression, anxiety, or psychotic-like symptoms in adolescence. However, poorer mental health was associated with the presence of severe CUD.