Trends in substance use and associations with internet use among Japanese high school students: A nationwide survey, 2018–2024

Aim To examine temporal trends in past‐year substance use among Japanese high school students and their associations with daily time spent on internet activities. Methods We analyzed pooled data from three nationwide repeated cross‐sectional surveys conducted in 2018, 2021, and 2024, including 142,567 Japanese high school students aged 16–18 years. Past‐year substance use (illicit drug and alcohol use and tobacco smoking) and daily time spent on internet activities (social networking services, online gaming, internet searching, video or music streaming, and online shopping or auctions) were assessed using self‐administered questionnaires. Associations between internet use and substance use were examined using survey‐weighted logistic regression models with restricted cubic spline functions to assess nonlinear patterns across exposure levels. Results Past‐year illicit drug use remained rare across the survey years (0.1%–0.3%). Alcohol use declined from 14.7% in 2018 to 8.0% in 2024, whereas tobacco smoking decreased from 1.8% to 1.3%. For illicit drug use, probabilities remained low at lower exposure levels but increased at higher levels, most notably for online shopping or auctions. Regarding alcohol use, a longer time spent on all internet activities was associated with higher probabilities, with steeper increases observed for social networking services and online shopping or auctions at higher exposure levels. For tobacco smoking, positive associations were most evident with networking services, online shopping, and auctions. Conclusion Activity‐specific patterns indicate heterogeneity in the associations between internet and substance use, highlighting the importance of considering the types of online activities alongside overall internet use.