IntroductionIndividuals with psychiatric conditions suffer disproportionately from tobacco-related morbidity and mortality, but the factors driving this relationship remain unclear. We used data from the Population Assessment of Tobacco and Health (PATH) to investigate whether associations between internalizing psychiatric symptoms and change in smoking heaviness (as measured by cigarettes per day (CPD) were mediated by self-reported respiratory symptoms, smoking risk perceptions, and cigarette dependence. MethodsThis study used data from PATH Waves 1 through 4 (2013–2017, n = 4,152). Psychiatric symptoms were indexed with the internalizing sub-scale of the Global Appraisal of Individual Needs-Short Screener (GAIN‐SS) among daily smokers. We fit auto-regressive structural equation models (SEM) to data from Wave 1–3 and 2–4 to determine the direct and indirect associations between internalizing symptom scores and CPD through each mediator. ResultsThe association between internalizing symptoms and CPD was mediated by cigarette dependence (indirect: B = 0.004, SE = 0.041, p = 0.023) and respiratory symptom severity (indirect: B = 0.018, SE = 0.097, p < 0.001). Internalizing symptoms predicted higher harm perceptions (B = 0.056, SE = 0.035, p < 0.001) but the indirect relationship with CPD was non-significant. Findings from Waves 2–4 replicated these results. ConclusionOur results indicate that cigarette dependence and respiratory symptom severity partially mediate the relationship between internalizing symptoms and CPD but risk perceptions were not significant predictors in our models. This suggests that efforts to reduce smoking among people with internalizing disorders should focus on decreasing nicotine dependence and increasing awareness of respiratory symptoms to encourage a quit attempt or switch to a less harmful source of nicotine.