"Social learning variables, peer attitudes (prevalence of norms favourable to deviant behaviour), personal approval (adoption of deviant norms), and peer behaviour have an effect on frequency of alcohol use and alcohol abuse. Alcohol expectancies and peer delinquency predict alcohol consumption of adolescents.

"Going out most evenings and the use of cannabis by peers and older siblings is associated with adolescents’ use of cannabis.

"Having school-related problems is a strong predictor in all stages of cannabis involvement (initiation of experimental use, initiation of regular use, progression to regular use, failure to discontinue, experimental use, failure to discontinue, regular use)."

Source

European Monitoring Centre for Drugs and Drug Addiction (2009), Preventing later substance use disorders in at-risk children and adolescents: a review of the theory and evidence base of indicated prevention. Thematic papers. Office for Official Publications of the European Communities, Luxembourg.