Cannabis use and the mental health of young people

Objective: To review the evidence on the mental health and psychosocial consequences of rising rates of cannabis use among young people in developed countries. Method: This paper critically reviews epidemiological evidence on the following psychosocial consequences of adolescent cannabis use: cannabis dependence; the use of heroin and cocaine; educational underachievement; and psychosis. Leading electronic databases such as PubMed have been searched to identify large-scale longitudinal studies of representative samples of adolescents and young adults conducted in developed societies over the past 20 years. Results: Cannabis is a drug of dependence, the risk of which increases with decreasing age of initiation. Cannabis dependence in young people predicts increased risks of using other illicit drugs, underperforming in school, and reporting psychotic symptoms. Uncertainty remains about which of these relationships are causal although the evidence is growing that cannabis is a contributory cause of psychotic symptoms. Conclusions: We face major challenges in communicating with young people about the most probable risks of cannabis use (dependence, educational underachievement and psychosis) given uncertainties about these risks and polarized community views about the policies that should be adopted to reduce them.