Outcomes of occasional cannabis use in adolescence: 10-year follow-up study in Victoria, Australia.

BACKGROUND Regular adolescent cannabis use predicts a range of later drug use and psychosocial problems. Little is known about whether occasional cannabis use carries similar risks. AIMS To examine associations between occasional cannabis use during adolescence and psychosocial and drug use outcomes in young adulthood; and modification of these associations according to the trajectory of cannabis use between adolescence and age 20 years, and other potential risk factors. METHOD A 10-year eight-wave cohort study of a representative sample of 1943 secondary school students followed from 14.9 years to 24 years. RESULTS Occasional adolescent cannabis users who continued occasional use into early adulthood had higher risks of later alcohol and tobacco dependence and illicit drug use, as well as being less likely to complete a post-secondary qualification than non-users. Those using cannabis at least weekly either during adolescence or at age 20 were at highest risk of drug use problems in young adulthood. Adjustment for smoking in adolescence reduced the association with later educational achievement, but associations with drug use problems remained. CONCLUSIONS Occasional adolescent cannabis use predicts later drug use and educational problems. Partial mediation by tobacco use raises a possibility that differential peer affiliation may play a role.