Effects of a peer-led intervention using theory of planned behavior to reduce smoking intentions and behavior among Ethiopian secondary students

Adolescent smoking is a major public health concern, contributing to long-term dependence, mental health disorders, risky behaviors, and poor educational outcomes. Peer-led, theory-driven school interventions, particularly those based on the Theory of Planned Behavior (TPB), have the potential to modify psychosocial determinants of smoking and reduce risky behaviors. This study assessed the effectiveness of a TPB-based, peer-led educational program on knowledge, psychosocial constructs, behavioral intentions, and smoking behavior among secondary school students in Northeast Ethiopia. A quasi-experimental pretest–posttest control group design was conducted in four public high schools in Northeast Ethiopia. A total of 1496 participants aged 15–24 years were allocated to intervention (n = 748) and control (n = 748) groups using cluster allocation at the school level to minimize contamination. The intervention comprised four 60-min peer-led sessions addressing knowledge, TPB constructs, and behavioral intentions. Outcomes were measured at baseline and 3 months post-intervention using validated self-administered questionnaires. Intervention effects were analyzed using generalized estimating equation (GEE) models, adjusting for parental education, family discussion on tobacco, baseline PBC, and knowledge. At 3 months, students in the intervention group showed significantly higher knowledge scores (β = 5.56; 95% CI: 5.10–6.01) and perceived behavioral control (β = 0.90), alongside reductions in positive smoking attitudes (β = −1.42), subjective norms (β = −1.42), intentions to smoke (β = −1.12), and current smoking prevalence from β = −0.34 to adjusted OR = 0.34 with 95% CI: 0.13–0.56 (p = 0.002)., whereas controls showed no meaningful change. TPB-based peer-led intervention significantly improved knowledge and PBC and reduced smoking attitudes, intention, and behavior of students, with a recommendation for its use in school-based tobacco prevention.