QuestionOppositional defiant and conduct disorders (ODD and CD) start early and persist, incurring high individual and collective costs. To inform policy and practice, we therefore asked: What is the best available research evidence on preventing and treating these disorders?Study selection and analysisWe sought randomised controlled trials (RCTs) evaluating interventions addressing the prevention or treatment of behaviour problems in individuals aged 18 years or younger. Our criteria were tailored to identify higher-quality RCTs that were also relevant to policy and practice. We searched the CINAHL, ERIC, MEDLINE, PsycINFO and Web of Science databases, updating our initial searches in May 2017. Thirty-seven RCTs met inclusion criteria—evaluating 15 prevention programmes, 8 psychosocial treatments and 5 medications. We then conducted narrative synthesis.FindingsFor prevention, 3 notable programmes reduced behavioural diagnoses: Classroom-Centered Intervention; Good Behavior Game; and Fast Track. Five other programmes reduced serious behaviour symptoms such as criminal activity. Prevention benefits were long term, up to 35 years. For psychosocial treatment, Incredible Years reduced behavioural diagnoses. Three other interventions reduced criminal activity. Psychosocial treatment benefits lasted from 1 to 8 years. While 4 medications reduced post-test symptoms, all caused important adverse events.ConclusionsConsiderable RCT evidence favours prevention.Clinical implicationsEffective prevention programmes should therefore be made widely available. Effective psychosocial treatments should also be provided for all children with ODD/CD. But medications should be a last resort given associated adverse events and given only short-term evidence of benefits. Policymakers and practitioners can help children and populations by acting on these findings.

To better address the mental health and substance use crises facing youth globally, a comprehensive approach, inclusive of mental health promotion is needed. A key component of mental health promotion is policy intervention to address the social and structural determinants of health. Importantly, youth should be engaged in these efforts to maximize relevancy and impact. Yet, while there is growing interest in the inclusion of youth in the policymaking process, there is a paucity of guidance on how to do this well. This environmental scan reports findings from a comprehensive search of academic and grey literature that was conducted using the electronic databases: CINAHL, ERIC, MEDLINE, PsycINFO, Google Scholar, and Google. Search terms included variations of ‘youth*’, ‘educat*’, ‘engage*’, ‘policy’ and ‘policy training’. Thirteen English language training programmes met inclusion criteria. Analysis identified marked differences in programme philosophy and focus by geographic region and highlights the need for enhanced evaluation and impact measurement moving forward. This paper makes a needed contribution to the evidence-base guiding this key mental health promotion strategy, which holds the potential to address critical gaps in approaches to youth mental health and substance use.

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