Trends in the co-use of alcohol and tobacco among Japanese adolescents: periodical nationwide cross-sectional surveys 1996–2017

Objectives This study aimed to assess trends in the prevalence of alcohol use depending on smoking behaviours and that of smoking depending on drinking behaviours among Japanese adolescents.Design This was a retrospective study using Japanese school-based nationwide surveys conducted between 1996 and 2017.Setting Surveyed schools, both junior and senior high schools, considered representative of the entire Japanese population, were sampled randomly.Participants We enrolled 11 584–64 152 students from 179 to 103 schools yearly. They completed a self-reported and anonymous questionnaire on smoking and drinking behaviour.Results Since 1996, the prevalence of alcohol use and smoking among adolescents decreased in each survey (p