A new study out of Brown University found that quitting smoking reduces symptoms of depression.1 From Brown's press release:
"Researchers tracked the symptoms of depression in people who were trying to quit and found that they were never happier than when they were being successful, for however long that was. The most illustrative and somewhat tragic subjects were the ones who only quit temporarily. Their moods were clearly brightest at the checkups when they were abstinent. After going back to smoking, their mood darkened, in some cases to higher levels of sadness than before. Subjects who never quit remained the unhappiest of all throughout the study. The ones who quit and stuck with abstinence were the happiest to begin with and remained at the same strong level of happiness throughout.
Looking at the data, (lead author Christopher Kahler) said, it is difficult to believe that smoking serves as an effective way to medicate negative feelings and depression, even if some people report using tobacco for that reason. In fact, he said, the opposite seems more likely — that quitting smoking eases depressive symptoms. “If they quit smoking their depressive symptoms go down and if they relapse, their mood goes back to where they were,” he said. “An effective antidepressant should look like that.”