ArticlesSmoking cessation and the course of major depression: a follow-up study
Introduction
In 1988, we noted that smokers attending a smoking-cessation clinic had a much higher than average frequency of past episodes of major depression,1 and even those who had been free of such episodes for many years were twice as likely as those who had never been depressed to start smoking again. In many clinical and epidemiological investigations, associations have been shown between smoking and major depression, and depression and inability to stop smoking;2, 3, 4, 5, 6, 7 although in other studies this association has not been shown.8, 9 A likely explanation seemed to be that smokers' depressive symptoms returned when they tried to stop smoking. However, in the early 1990s, depression was not thought to be a symptom of smoking withdrawal. Therefore, we assessed smokers, with and without a history of major depression, and noted that depressive symptoms were significantly more frequent and intense during nicotine withdrawal in smokers with a history of major depression than in those without such a history.10
Some smokers also had episodes of major depression. Unlike withdrawal symptoms, these episodes did not subside within 1 or 2 weeks of stopping smoking and sometimes did not start for several weeks after cessation.7, 11, 12 However, many of these findings were merely anecdotal and did not control for the incidence of depression among individuals with a history of depression who continued to smoke. Any individual with a history of major depression is more likely to develop depression than people without that history, irrespective of whether they have stopped smoking.13 A study of the efficacy of an antidepressant drug to help smokers with a history of major depression to stop smoking gave us an opportunity to prospectively investigate this issue.
In cessation studies, abstinent participants are normally followed up for at least 6 months to check whether differences between drug and placebo groups disappear after treatment is withdrawn. We followed up all participants for 6 months after active treatment ended, and recorded smoking status and onset of new psychiatric symptoms or diagnoses. All people in the study had a history of major depression; hence we were able to prospectively assess the effect of smoking cessation on the risk of relapse to major depression, while controlling for participants' history of depression.
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Participants
Smokers were mostly recruited by newspaper advertisements. We screened respondents by telephone for history of smoking, depression, and use of antidepressant drugs. Smokers who had no history of depression were referred to other programmes, as were smokers who had a history of major depression and who had taken antidepressant drugs in the past 6 months. If phone contact suggested that the candidates were suitable a personal interview was arranged. Interviews included the sections of the
Treatment
Eligible smokers were randomly assigned sertraline or an identical placebo. They were told that the study drug was an antidepressant that would take several weeks to work, and were advised to select a day to stop smoking as close to 21 days after starting treatment as possible. 9 weeks after the start of the study, participants reported their smoking status, which was confirmed by serum cotinine concentration. Sertraline or placebo was gradually reduced and stopped in the next 2 weeks. We
Results
100 smokers came to their quit appointment on their chosen date to stop smoking (3 weeks after start of treatment). Follow-up data were obtained for 76 participants. They smoked a mean of 27·4 (SD 9·2) cigarettes daily. Mean age was 43·7 years (11·3). 49 (64%) were women and 65 (86%) were white. 43 (57%) had had recurrent episodes of major depression and 58 (76%) had sought professional help. Mean time since their last depressive episode was 7–4 (7·3) years. The table shows baseline
Discussion
Smokers with a history of major depression who stopped smoking were seven times more likely to have a recurrence of major depression than people who continued to smoke. Our study was prospective and we controlled for a history of depression. However, it was a follow-up study not a randomised trial.
A randomised controlled trial of the relation between smoking cessation and depression is neither ethical nor practical. Smokers cannot be randomly selected to abstain from or to continue smoking, or
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