Smoking and E-cigarette Use in Smoke-free Schools among Secondary School Students in Thailand: A Multicenter Prospective Cohort Study

Introduction: Despite legal prohibitions, electronic cigarette (E-cigarette) use among Thai adolescents is increasing. While smoke-free school policies have shown promise in reducing youth tobacco use, longitudinal evidence of their effectiveness in Thailand remains limited. This study aimed to examine the impact of smoke-free school environments on cigarette and E-cigarette use among secondary school students in four regions of Thailand. Methods: A multicenter prospective cohort study was conducted from May 2023 to November 2024 across four points. A total of 5555 students in Grades 7 and 8 from smoke-free and nonsmoke-free schools were recruited via multistage sampling, with 1952 students completing all four data collection rounds. Data were collected via a validated self-administered online questionnaire. Descriptive statistics summarized participant characteristics and outcomes. Generalized estimating equations (GEEs) were used to assess differences in smoking-related behaviors, adjusting for potential confounders. Results: Students in smoke-free schools consistently reported a lower prevalence of current smoking (4.2%–4.5% vs. 4.9%–6.5%), lower smoking intention, and lower E-cigarette use intention over time. Multivariable GEE analysis revealed significantly reduced odds of smoking (adjusted odds ratio [AOR] = 0.60; 95% confidence interval [CI]: 0.43–0.86), smoking intention (AOR = 0.74; 95% CI: 0.62–0.90), and E-cigarette use intention (AOR = 0.67; 95% CI: 0.55–0.82) among students in smoke-free schools. However, they reported higher odds of witnessing vaping on campus (AOR = 1.36; 95% CI: 1.19–1.57). Conclusion: Smoke-free school policies effectively reduce adolescent smoking and E-cigarette use intentions, although additional strategies are needed to reduce vaping exposure in school settings.