Prevention, early intervention, harm reduction, and treatment of substance use in young people.

We did a systematic review of reviews with evidence on the effectiveness of prevention, early intervention, harm reduction, and treatment of problem use in young people for tobacco, alcohol, and illicit drugs (eg, cannabis, opioids, amphetamines, or cocaine). Taxation, public consumption bans, advertising restrictions, and minimum legal age are effective measures to reduce alcohol and tobacco use, but are not available to target illicit drugs. Interpretation of the available evidence for school-based prevention is affected by methodological issues; interventions that incorporate skills training are more likely to be effective than information provision-which is ineffective. Social norms and brief interventions to reduce substance use in young people do not have strong evidence of effectiveness. Roadside drug testing and interventions to reduce injection-related harms have a moderate-to-large effect, but additional research with young people is needed. Scarce availability of research on interventions for problematic substance use in young people indicates the need to test interventions that are effective with adults in young people. Existing evidence is from high-income countries, with uncertain applicability in other countries and cultures and in subpopulations differing in sex, age, and risk status. Concerted efforts are needed to increase the evidence base on interventions that aim to reduce the high burden of substance use in young people.