Adolescent precursors of cannabis dependence: findings from the Victorian Adolescent Health Cohort Study.

BACKGROUND Dependence increases the likelihood of adverse consequences of cannabis use, but its aetiology is poorly understood. AIMS To examine adolescent precursors of young-adult cannabis dependence. METHOD Putative risk factors were measured in a representative sample (n=2032) of secondary students in the State of Victoria, Australia, six times between 1992 and 1995. Cannabis dependence was assessed in 1998, at age 20-21 years. RESULTS Of 1601 young adults, 115 met criteria for cannabis dependence. Male gender (OR=2.6, P < 0.01), regular cannabis use (weekly: OR=4.9; daily: OR=4.6, P=0.02), persistent antisocial behaviour (linear effect P=0.03) and persistent cigarette smoking (linear effect P=0.02) independently predicted cannabis dependence. Neither smoking severity (P=0.83) nor persistent psychiatric morbidity (linear effect P=0.26) independently predicted dependence. Regular cannabis use increased risk only in the absence of persistent problematic alcohol use. CONCLUSIONS Weekly cannabis use marks a threshold for increased risk of later dependence, with selection of cannabis in preference to alcohol possibly indicating an early addiction process.