Prevalence and characteristics of above-recommended-dose non-medical use of over-the-counter drugs in Japan: a descriptive cross-sectional study using a nationwide online survey

BACKGROUND: This study aimed to describe the prevalence, acquisition routes, and help-seeking behavior of non-medical use of over-the-counter (OTC) drugs among Japanese online survey respondents. METHODS: A cross-sectional online survey using the Japan "Society and New Tobacco" Internet Survey (JASTIS) was conducted from February 23 to March 31, 2025. Past 12-month use, misuse defined as use above the recommended dose, and non-medical use among respondents reporting above-recommended-dose use of seven OTC drug categories were assessed. Acquisition sources and help-seeking behavior were also examined. Inverse probability weighting was applied to mitigate selection bias from non-probability sampling. RESULTS: A total of 25,424 respondents aged 15-84 years were included. The weighted prevalence of non-medical OTC drug use was 6.8%. Combination cold medicines had the highest prevalence of non-medical use (3.8%). Approximately two-thirds of respondents reporting non-medical OTC drug use reported involvement of multiple drug categories. Pharmacies or drugstores were the primary acquisition source across all drug categories (38.3-45.9%). A higher prevalence of non-medical use was observed among younger respondents (15-24 years, 11.8%) and respondents with psychiatric disorders (21.3%). Fewer than half (46.9%) of respondents reporting non-medical use sought help. CONCLUSIONS: Using the operational definition, 6.8% of Japanese online survey respondents reported non-medical OTC drug use after above-recommended-dose use, with frequent involvement of multiple drug categories and low help-seeking. These findings indicate the need to address drug-specific acquisition patterns and to develop accessible and non-stigmatizing support services for this population in future policy reforms.