Longitudinal association between smoking abstinence and depression severity in those with baseline current, past, and no history of major depressive episode in an international online tobacco cessation study.

INTRODUCTION: We use multilevel modeling (MLM) to parse out the effects of time-varying smoking abstinence and baseline depression (history and severity) on depression severity over one year. METHODS: Participants were 1,000 smokers recruited worldwide for an online randomized controlled tobacco cessation trial. We examined whether changes in depression severity over time were associated with self-reported 7-day point prevalence smoking status assessed at 1-,3-,6-, and 12-month follow-up using baseline major depressive episode (MDE) history and baseline depression severity as time-invariant covariates. We present depression severity means and smoking abstinence at each follow-up. RESULTS: Regardless of concurrent abstinence status, baseline MDE history was significantly related to depression severity over time: those reporting a past MDE had worse depressive symptoms over time compared with those reporting no MDE history. Baseline depression severity interacted significantly with time-varying abstinence status: for every 1-unit increase in baseline scores on the Center for Epidemiological Studies Depression Scale (CES-D), individuals who were smoking at follow-up reported CES-D scores that were 0.17 points higher than those who were abstinent. In this context, nicotine dependence, gender, age, or marital status did not affect depression severity. CONCLUSIONS: In the context of cessation, having an MDE history plays a significant role in the trajectory of depression severity over the course of one year, regardless of abstinence status. Abstinence is related to lower depressive symptoms at each follow-up, and this effect was stronger at higher levels of baseline depression severity. IMPLICATIONS: This study indicates that depressive symptoms are not exacerbated among individuals who are quitting smoking at 1-, 3-, 6- and 12-month follow-ups. Depression severity is worse with a baseline history of major depressive episode. Further, those with high baseline depression severity who continue smoking have worse depressive symptoms throughout a one-year period compared to their abstinent counterparts.