Background: Smokers with a history of major depression who attempt to stop smoking have a higher risk of failure than non-depressed smokers. Anecdotal and post-hoc data suggest that those who successfully abstain are at increased risk of depression compared with individuals who continue to smoke. However, these studies confound effects of abstinence and history of depression. We aimed to assess whether there is an increased risk of depression and for how long that increase lasts.
Methods: We enrolled 100 smokers (>1 pack per day) with a history of major depression, but who were currently free from major depression and had not been on antidepressant medicine for at least 6 months, in a 2-month smoking-cessation trial. The primary outcome was recurrence of major depression, which we assessed by structured clinical interviews 3 and 6 months after the end of treatment. We verified smoking status by serum-sample cotinine concentrations.
Findings: 76 participants (42 successful abstainers, 34 smokers) were followed up. 13 abstainers and two smokers had an episode of major depression (odds ratio 7.17 [95% CI 1.5-34.5]; Kaplan-Meier survival curve, log-rank statistic 9.11 [p=003]). Risk of major depression was similar between the first and second 3 months of follow-up.
Interpretations: Smokers with a history of depression who abstain from smoking are at significantly increased risk of developing a new episode of major depression. This risk remains high for at least 6 months.