The impact of youth internalising and externalising symptom severity on the effectiveness of brief personality-targeted interventions for substance misuse: A cluster randomised trial

•Personality-targeted interventions reduce binge drinking in high-risk youth.•Youth with high (vs. low) externalising symptoms benefitted more from the intervention.•Personality-targeted interventions may effectively treat dually diagnosed youth.•The presence of high internalising symptoms didn't moderate intervention effects.