BACKGROUND:In recent years, drug prevention networks and drug education programs started to utilize web-based or smartphone applications as novel prevention tools, testing their efficacy as compared to face-to-face prevention. OBJECTIVE: Our study aimed to assess potentials of an interactive application called Once Upon a High (VoltEgySzer). METHODS: Students of two vocational and two high schools filled in a questionnaire at a baseline (T0) and a two month follow-up (T1) data collection session. Students of one vocational (VS1) and one high school (HS1) downloaded the Once Upon a High app (app group), whereas students from the other vocational (VS2) and high school (HS2) did not (nonapp group). T0 and T1 questionnaires contained demographic variables, items regarding substance use characteristics with regard to both legal and illegal substances, including novel psychoactive substances (NPS), exercise habits, knowledge about psychoactive substances, attitudes toward substance users and validated instruments measuring the severity of tobacco (Fagerström Test for Nicotine Dependence), alcohol (AUDIT), cannabis (CAST) and synthetic cannabinoid (sCAST) consumption. Beliefs about substance use (BASA) and perceived self-efficacy (GSE) were also measured. At T1, members of the app group provided additional evaluation of the application. RESULTS: 386 students participated in T0 session and followed by a drop-out, 246 students took part in T1 data collection procedure. Alcohol was the most frequently consumed psychoactive substance (92.1% lifetime use), followed by tobacco (68% lifetime use) and cannabis (13.2% lifetime use). Synthetic cannabinoids were the most commonly used NPS (7.2%). Decreased self-efficacy (Beta= -0.29, p<0.05) and increased daily physical exercise frequencies (Beta= 0.04, p<0.001) predicted higher frequencies of past month energy drink consumption, whereas elevated past month alcohol consumption was mainly predicted by a decrease in negative attitudes toward substance users (Beta= -0.13, p<0.05). Once Upon a High was found to be effective in increasing a) knowledge about the risks of psychoactive substances and b) perceived self-efficacy but not in reducing substance use. The roleplay module of the application was found to be the most preferred and beneficial aspect of the app. CONCLUSIONS: Once Upon a High app can be a useful tool to assist preventive intervention programs by increasing knowledge and self-efficacy, however, its efficacy in reducing or preventing substance use needs to be improved and further studied. Additional potentials of the app need testing.