Effects of the social norms intervention on norm perceptions, binge drinking and alcohol-related harms: A cluster-randomised controlled trial.

The study aimed to investigate if the school-based social norms intervention was effective in reducing misperceptions, heavy alcohol use and alcohol-related harms among Danish pupils aged 13-17 years. In total 38 schools were included in a cluster-randomised controlled trial and allocated to either intervention ( = 641) or control group ( = 714) during 2015/2016. Both groups completed an online survey before the intervention and 3 months after baseline. intervention provided normative feedback tailored for each school-grade using three communication channels: classroom sessions, posters and web application. Outcome measures were overestimation of peers' lifetime binge drinking, binge drinking (5 or more drinks on one occasion) and alcohol-related harms. Intervention effects at follow-up were examined using multilevel logistic regression models. Pupils in the intervention group were less likely to overestimate peers' lifetime binge drinking compared to those in the control group (OR: 0.52, 95%CI: 0.33-0.83) and were less likely to report two or more alcohol-related harms (OR: 0.59, 95%CI: 0.37-0.93). Overall, no significant effect of the intervention was found on binge drinking. However, among pupils stating it would be ok, if they drank more ( = 296), a preventive effect was found on binge drinking four or more times during the last 30 days (OR: 0.37, 95%CI: 0.15-0.95). Additionally, the intervention effect on overestimation was higher among pupils who reported binge drinking at baseline. Receiving the intervention had a positive effect on norm perceptions and alcohol-related harms. We also found that the intervention effect differed by baseline status of alcohol use.