First positive reactions to cannabis constitute a priority risk factor for cannabis dependence

Aim To assess the association between first reactions to cannabis and the risk of cannabis dependence. Design A cross-sectional population-based assessment in 2007. Setting A campus in a French region (Champagne-Ardennes). Participants A total of 1472 participants aged 18-21 years who reported at least one life-time cannabis consumption, of 3056 students who were screened initially [the Susceptibility Addiction Gene Environment (SAGE) study]. Measurements Positive and negative effects of first cannabis consumptions, present cannabis dependence and related risk factors were assessed through questionnaires. Findings The effects of first cannabis consumptions were associated dose-dependently with cannabis dependence at age 18-21 years, both according to the transversal approach of the SAGE study and to the prospective cohort of the Christchurch Health and Development Study (CHDS) assessed at the age of 25 years. Participants of the SAGE study who reported five positive effects of their first cannabis consumption had odds of life-time cannabis dependence that were 28.7 (95% confidence interval: 14.6-56.5) higher than those who reported no positive effects. This association remains significant after controlling for potentially confounding factors, including individual and familial variables. Conclusions This study suggests an association between positive reactions to first cannabis uses and risk of life-time cannabis dependence, this variable having a central role among, and through, other risk factors.