What can explain the differential effectiveness between two similar school-based universal programmes for prevention of substance use? The us-eu cross-country study

Background: National context is known to influence substance use, a common target of prevention. However, trials conducted in different contexts have rarely been compared. Two similar prevention programmes targeting substance use were implemented in different contexts and had diverse outcomes. “Unplugged”, conducted in the E.U., was successful in reducing drunkenness and cannabis use. “Take Charge of Your Life” (TCYL), conducted in the U.S., was effective in reducing marijuana use and had an apparent iatrogenic effect on alcohol and cigarette use. Objective: To compare two prevention programmes implemented in different contexts, “Unplugged” and “TCYL”. Methods: Four assessors evaluated materials and implementations using a pre-defined form. Prevalence rates of substance use in each study group were compared using chi-square tests. Contextual factors such as countryspecific policies and prevalence of substance use were also compared. Results: Overall there were few differences between “Unplugged” and “TCYL” content. Class teachers delivered “Unplugged” and trained police officers delivered “TCYL”. U.S. control students had greater exposure to other prevention interventions. Baseline prevalence of alcohol and cannabis use was higher in the U.S. sample. Policies appeared to be more restrictive in the U.S for all substances. Prevalence of smoking and drunkenness were greater in E.U. countries; cannabis consumption was greater in the U.S. Conclusion: Proximal factors such as programme delivery and exposure in the U.S. control group to prevention programming appear to be influential in determining the differential effectiveness of “Unplugged” and “TCYL”. The impact of contextual factors remains unclear, and needs to be explored employing common protocols in future crossnational tudies.