Age and sex differences in factors associated with the onset of cannabis use: a cohort study.

OBJECTIVE To investigate age and sex differences in factors associated with the onset of cannabis use among adolescents. METHODS A representative sample of schoolchildren from secondary schools in Barcelona (n=1056) was selected and followed-up from the first to the fourth year of secondary education (7-10th grades). The participants completed a self-administered lifestyle questionnaire each year. Multilevel logistic regression models were used for each year and sex to analyse predictors of cannabis use; the second level was adjusted by school. RESULTS Onset of cannabis use during follow-up was associated with a prior history of tobacco smoking [odds ratio (OR)=7.7 in boys; OR=3.8 in girls], alcohol consumption (OR=6.4 in boys; OR=3.2 in girls), antisocial behavior (OR=2.8 in boys; OR=2.2 in girls), intention to use drugs (OR=3.5 in boys; OR=4.2 in girls), drug use among friends (OR=2.5 in boys; OR=3.7 in girls) and spending leisure time in bars or discos (OR=2.1 in boys; OR=3.8 in girls). Moreover, among girls, attending state schools (OR=2.9), low academic performance (OR=5.7) and living in a single-parent family (OR=2.0) also independently predicted cannabis use. CONCLUSIONS This study reveals a wide array of predictive factors in cannabis use onset that largely differed by age and sex. The results support the role of tobacco and alcohol, as well as the influence of drug use among friends, and the importance of leisure time patterns as facilitators of cannabis use.