In Europe, cannabis is used at least monthly by 20% of students aged 15-16 (Espad 2011). These data raise our concern for many reasons: cannabis is an addictive substance, and has been associated with several health consequences, like psychosis, other psychiatric symptoms, attention deficit etc. Cannabis was the most frequently used drug reported as reason for entering treatment, although with large variations among countries. Cannabis is considered a gateway drug, giving access to use of other drugs.
Only a minority of cannabis users experienced these effects, and usually those with a more intensive use. However the prevention interventions usually address first use of cannabis, instead of the progression from experimentation and intensive use, and this is because the knowledge about the determinants of progression is lacking or very weak.
Adolescence is the life period during which most part of young people start do use drugs, and for these reasons school is a privileged setting for prevention.
The study of the determinants of adolescent behaviors is the base for prevention interventions. Risk protective factors more frequently addressed by interventions are peer influence, communication skills, knowledge, refusal skills. Indeed, most part of intervention are based on the development of life skills to tackle these factors.
Most effective interventions are based on a mix of theories, including social learning (Bandura 1977) and social norms theories (Durkeim 1951), but also on psychological vulnerability (Sher 2000). The average effect size of such interventions is around 30% (RR=0.7), with large variations among interventions (Faggiano 2014).
The effectiveness of interventions could probably be strongly improved if they are implemented together of other kind of interventions acting on the environment, not only focused on cannabis prevention, but also on tobacco and alcohol consumption, considered to be gateway drugs for cannabis use.