Cannabis use among young people is common, with peak incidence of onset of use occurring in adolescence 1–2. Use is associated with many adverse health and social outcomes, with these associations being most clearly apparent in relation to more extreme cannabis use phenotypes. This could simply reflect a dose–response relation between cannabis use and harm; however, it might also suggest a distinct phenotype of problem cannabis use whose effects, and possibly antecedents, are different. Instruments to measure problem cannabis use have been developed to allow investigation of these questions 3.
