Tobacco-Use Susceptibility and Ever-Use Categories in Relation to Depressive Symptoms Among Undergraduates at a Chinese University: A Cross-Sectional Study.

Background/Objectives: Tobacco involvement and depression frequently co-occur among young people, but Chinese campus studies rarely examine mental health across tobacco susceptibility and use categories. We examined cross-sectional associations of three mutually exclusive categories (firmly non-susceptible 'never users', susceptible never users, and 'ever users') with depressive symptoms and life satisfaction. Methods: A cross-sectional survey of 415 undergraduates (75.4% female) was conducted in southeastern China in December 2025. Primary analyses used trend tests and adjusted regression for depressive symptoms; secondary analyses examined susceptibility components and a descriptive bootstrap decomposition of the life-satisfaction association; sensitivity analyses evaluated alternative specifications, model diagnostics, and response quality. Results: Mean CES-D-10 scores were 9.29, 11.55, and 13.06 across the three categories (trend p < 0.001), and probable depression prevalence was at 46.5%, 60.7%, and 68.1% (p = 0.002). Each one-category increase was associated with a 1.74-point-higher adjusted CES-D-10 score (HC3 95% CI: 0.76 to 2.73) and 65% higher adjusted odds of probable depression (95% CI: 1.17 to 2.33). In a descriptive cross-sectional decomposition, the indirect association with lower life satisfaction through concurrent depressive symptoms was -0.071 (bootstrap 95% CI: -0.124 to -0.027); this does not establish causal mediation. Ever users who remained susceptible scored 4.82 points (HC3 95% CI: 2.63 to 7.00) above firmly non-susceptible never users, whereas the 12 non-susceptible ever users did not differ detectably. Conclusions: The findings identify a cross-sectional mental-health gradient across tobacco susceptibility/use categories, without establishing temporal direction. Replication in longitudinal, multi-site samples is required before reciprocal screening and referral are implemented at scale.