smokingA study published in the British Medical Journal reports that quitting smoking had a simillar positive effect on mood as an antidepressant. The researchers did an analysis of 26 studies using a technique called a “meta-analysis” and looked at changes in mental health (anxiety, depression, mixed anxiety and depression, quality
of life, positive affect, and stress) at ≥6 weeks’ post–smoking cessation compared with changes after the same amount of time among people who continued to smoke.

In the studies, at between 6 and 12 months after smoking cessation, smoking cessation, compared with continued smoking, was associated with significant decreases in anxiety, depression, mixed anxiety and depression, and stress and significant increases in psychological quality of life and positive affect
(all measured via questionnaires). The effect size was similar between participants from general populations and those with physical or psychiatric illnesses.

In his review in the New England Journal of Medicine’s Journal Watch, Paul S. Mueller, MD, MPH, FAC writes that –

In this study, smoking cessation was associated with improved mental health outcomes. Although these observational associations do not prove causality, they do challenge widely held beliefs that smoking relieves psychological symptoms and that trying to quit smoking aggravates such symptoms….these results should inspire us to be more proactive in encouraging smoking cessation among patients with anxiety and depression.

The review article itself is

Taylor G et al. Change in mental health after smoking cessation: Systematic
review and meta-analysis. BMJ 2014 Feb 13; 348:g1151.