PURPOSE: To examine the relationship of the early initiation of cannabis use with other high risk behaviors and with psychosocial and health-related correlates in 15-year-old adolescents in six European countries.

METHODS: This study reports on nationwide cross-sectional surveys in six European countries in 2001-2002, within the framework of the World Health Organization's collaborative study, Health Behaviour in School-aged Children (HBSC). Data were collected through anonymous questionnaires self-completed in classrooms. Descriptive and multivariate analyses were used to assess differences between countries in age of first cannabis use and associations with health and related psychosocial variables.

RESULTS: The prevalences of lifetime and last-year cannabis use ranged from 30.7% and 27.5%, respectively, in the Czech Republic, to 5.4% and 4.1%, respectively, in Greece. Age at first use was lower in the high prevalence countries than in countries with lower prevalence. For 15-year-olds, frequent use of tobacco and alcohol and other risk behaviors were correlated with early (13-15 years old) and especially very early (< or = 13 years old) cannabis initiation.

CONCLUSIONS: Although different patterns of prevalence and age of initiation were observed between participating countries, early cannabis use was almost uniformly associated with higher odds of more frequent use of cannabis and other substances, and with a common set of other problems. Our findings suggest that prevention of drug abuse must commence in preadolescence.