How effective is a social norms programme in changing perceived injunctive norms about drug use?

Social norm theory suggests that students often overestimate the frequency and quantity of drug use among their peers (descriptive norms) as well as how acceptable their peers feel these risky behaviours to be (injunctive norms) and tend to match their own behaviour to this incorrect perception. This study aims to investigate whether a Danish social norms based intervention (The GOOD Life) using both descriptive and injunctive normative information may change students perception of peers' attitudes towards smoking, drinking and using cannabis.In total 38 schools were included in a cluster-randomised controlled trial and allocated to either intervention (n = 641) or control group (n = 714) during 2015/2016. Students (aged 13-17 years) from both groups completed an online survey before the intervention and 3 months after baseline. The GOOD Life intervention provided normative feedback tailored for each school-grade using three communication channels: classroom sessions, posters and web application. Outcome measures were perception of peers' attitude towards: smoking, drinking alcohol, getting drunk and using cannabis. All with five response options from 'never okay' (1) to 'okay' (5). Intervention effects at follow-up were examined using ordinal logistic regression models and marginal effect-estimates.Students in the intervention group were less likely to perceive peers to approve of smoking (Coef: -0.22, p = 0.04, 95\-0.43; -0.01]). The marginal effect estimates showed that compared to the control group, students in the intervention group were 5\ 3\\% less likely to perceive that peers think it is okay to smoke frequently. No significant effects were found for injunctive norms regarding alcohol consumption and cannabis use.The intervention The GOOD life has potential to produce change in perceived injunctive norms among Danish adolescents.Prevention programmes should thoroughly consider how to incorporate injunctive normative feedback.