Background Young people have the highest rate of drug use worldwide. Recent data from Mexico in this population show that the prevalence of illicit drug use doubled between 2011 and 2016 (2.9%-6.2%), with marijuana being the one with the highest increase (2.4%-5.3%), but also point out that alcohol and tobacco use have remained steady or decreased. Mexican adolescents are at high risk for drug use owing to a low perception of risk and the availability of drugs. Adolescence is an ideal period to reduce or prevent risky behaviors using evidence-based strategies. Objective In this study, we aimed to test the short-term effectiveness of a mobile intervention app (“What Happens if you Go Too Far?” [“¿Qué pasa si te pasas?”]) that seeks to increase risk perception of tobacco, alcohol, and marijuana use in a sample of Mexican high school students. Methods A nonexperimental evaluation based on pretest-posttest design was used to measure the effectiveness of a preventive intervention using a mobile app, “What Happens If You Go Too Far?” The dimensions analyzed were knowledge of drugs and their effects, life skills, self-esteem, and risk perception. The intervention was conducted on a high school campus with 356 first-year students. Results The sample included 359 first-year high school students (mean 15, SD 0.588 years; women: 224/359, 62.4% men: 135/359, 37.6%). The intervention increased the overall risk perception of tobacco (χ24=21.6; P<.001) and alcohol use (χ24=15.3; P<.001). There was no significant difference in the perception that it is dangerous to smoke 5 cigarettes, and there was a marginal difference in the perception that it is very dangerous to smoke 1 cigarette or to use alcohol or marijuana. We used a generalized estimating equation method to determine the impact of the variables on risk perception. The results showed that knowledge about smoking increased the risk perception of smoking 1 cigarette (odds ratio [OR] 1.1065, 95% CI 1.013-1.120; P=.01), and that knowledge about marijuana use (OR 1.109, 95% CI 1.138-1.185; P=.002) and self-esteem (OR 1.102, 95% CI 1.007-1.206; P=.04) produced significant increases in the risk perception of consuming 5 cigarettes. Resistance to peer pressure and assertiveness also increased the perceived risk of using tobacco and alcohol. Conclusions The intervention has the potential to increase the perception of risk toward drug use in high school students by providing knowledge about the effects and psychosocial risks of drug use and by strengthening life skills that are associated with increased risk perception. The use of mobile technologies in intervention processes may broaden the scope of preventive work for adolescents.

BACKGROUND Young people have the highest rates of drug use worldwide. Mexican adolescents are at high risk for drug use due to a low perception of risk and the availability of drugs. Adolescence is an ideal period to reduce or prevent risk behaviors with evidence-based strategies. OBJECTIVE To evaluate the short-term effectiveness of a mobile application to increase risk perception of tobacco, alcohol, and marijuana use in a sample of Mexican high school students. METHODS A non-experimental pre-post evaluation was used to measure the effectiveness of a preventive intervention using a mobile application, “What Happens If You Go Too Far?” The dimensions analyzed were knowledge about drugs and their effects, life skills, self-esteem, and risk perception. The intervention was carried out on a high school campus with 356 first-year students. RESULTS The intervention increased the overall risk perception for tobacco and alcohol use, the perception that it is dangerous to smoke five cigarettes, and the perception that it is very dangerous to smoke one cigarette or to use alcohol or marijuana. Tobacco knowledge, marijuana knowledge, resistance to peer pressure, self-esteem, and assertiveness significantly increased the perceived risk of using these drugs. CONCLUSIONS The intervention has the potential to increase the perception of risk towards drug use in high school students by providing knowledge about the effects and psychosocial risks of drug use, and by strengthening life skills that are associated with increased risk perception. The use of mobile technologies in intervention processes may broaden the scope of preventive work in adolescents.