Data from Western countries suggest that up to half of adolescents have used cannabis at least once, and up to 10% may develop cannabis abuse or dependence. To examine the natural history of cannabis use, German investigators analyzed 4- and 10-year follow-up data from 3021 youth (ages 14–24 years at baseline) enrolled in a prospective population-based cohort study. Cannabis use and dependence were measured using the Munich Composite International Diagnostic Interview-Substance Abuse Module (CIDI-SAM).

• At baseline, 7% had used cannabis once only; 11% had used it 2 to 4 times only, and 16% had used it 5 times or more (repeated use).
• Of those who had repeated cannabis use at baseline, 56% still used it 4 years later, and 46% still used it 10 years later.
• Predictors of repeated use at 10-year follow-up included repeated use at baseline, younger age of initial use, male gender, drug-using peers, distressing life events, and alcohol dependence.
• Cannabis abuse or dependence was found in 12% of subjects at baseline, 15% at 4 years, and 13.5% at 10 years.
• Cannabis dependence at baseline was significantly associated with dependence at 10-year follow-up.

Comments by Michael Levy, PhD
This study found that cannabis dependence early in life heightened vulnerability to a chronic cannabis disorder well into adulthood. Early interventions to delay first use and reduce frequency of use in adolescents and young adults may be helpful in offsetting future difficulties, since both these factors related to cannabis dependence later in life.