Patterns of cannabis-use during adolescence and their association with harmful substance use behaviour:findings from a UK birth cohort

Background: Evidence on the role of cannabis as a gateway drug is inconsistent. We characterise patterns of cannabis-use among UK teenagers aged 13 to 18, and assess their influence on problematic substance use at age 21 years.Methods: We used longitudinal latent class analysis to derive trajectories of cannabis use from self-report measures in a UK birth cohort. We investigated: a) factors associated with latent class membership; and b) whether latent class membership predicted subsequent nicotine dependence, harmful alcohol use and recent use of other illicit drugs at age 21 years.Results: 5,315 adolescents had three or more measures of cannabis-use from age 13 to 18 years. Cannabis-use patterns were captured as four latent classes corresponding to ‘non-users’ (80.1%), ‘late-onset occasional’ (14.2%), ‘early-onset occasional’ (2.3%), and ‘regular’ users (3.4%). Sex, mother’s substance use, and child’s tobacco use, alcohol consumption and conduct problems were strongly associated with cannabis-use. At age 21 years, compared with the non-user class, late-onset occasional, early-onset occasional and regular cannabis user classes had higher odds of nicotine dependence (OR=3.5, 95%CI 0.7-17.9; OR=12.1, 95%CI 1.0-150.3; and OR=37.2, 95%CI 9.5-144.8, respectively); harmful alcohol consumption (OR=2.6, 95%CI 1.5-4.3; OR= 5.0, 95%CI 2.1-12.1; and OR=2.6, 95%CI 1.0-7.1, respectively); and other illicit drug use (OR=22.7, 95%CI 11.3-45.7; OR=15.9, 95%CI 3.9-64.4; and OR=47.9, 95%CI 47.9-337.0, respectively).Conclusion: One fifth of the adolescents in our sample followed a pattern of occasional or regular cannabis-use, and these young people were more likely to progress to harmful substance use behaviours in early adulthood