Many people believe that smoking gives them a mental lift. After all, they experience irritability, anxiety, and depression when they have not smoked for a while, and these feelings are relieved by smoking.

But actually it is giving up smoking—not engaging in it—that confers mental benefits, a meta-analysis published February 13 in the British Medical Journal suggests.

The senior investigator was Paul Aveyard, a professor of behavioral medicine at the University of Oxford in England.

The meta-analysis included 26 studies that measured subjects’ mental health before and after quitting. The included studies examined six measures of mental health: anxiety, depression, mixed anxiety and depression, positive affect, psychological quality of life, and stress. Eleven of the studies were cohort studies, 14 were secondary analyses of cessation interventions, and one was a randomized trial.

Fourteen studies enrolled smokers from the general population, four enrolled patients with psychiatric disorders, three enrolled patients with chronic physical conditions, two enrolled patients with either psychiatric or physical conditions, two enrolled pregnant women, and one enrolled patients after surgery. Subjects smoked on average 20 cigarettes a day and scored 5.4 on the Fagerstrom test measuring nicotine dependence, indicating moderate dependence.

Finally, mental health outcomes were evaluated from seven weeks to nine years after baseline, but on average six months later.

Four studies reported a change in anxiety from baseline to follow-up, with follow-ups ranging from seven weeks to 12 months. Compared with continuing to smoke, quitting smoking was associated with a significant decrease in anxiety from baseline to follow-up.

Five studies reported a change in mixed anxiety and depression from baseline to follow-up. Compared with continuing to smoke, quitting smoking was associated with a significant decrease in mixed anxiety and depression from baseline to follow-up, which ranged from six months to three years.

Ten studies reported a change in depression from baseline to follow-up, with follow-up ranging from 11 weeks to five years. Compared with continuing to smoke, quitting smoking was associated with a significant decrease in depression from baseline to follow-up.

Three studies reported a change in stress from baseline to follow-up, with follow-up from six months to six years. Compared with continuing to smoke, quitting smoking was associated with a significant decrease in stress.

There thus appears to be ample evidence that smoking cessation is associated with improvements in depression, anxiety, and stress. And the strength of the association, the researchers found, appears to be similar for both the general population and clinical populations, including those with mental disorders.

“We believe that the data are valid and propose three possible explanations for the association,” the researchers said. “The first is that smoking cessation causes the improvement in mental health, the second is that improving mental health causes cessation, and the third is that a common factor explains both improved mental health and cessation.”

The researchers indicated that they preferred the first explanation. One reason is that “in some but not all of the studies we could calculate the change in mental health in quitters and continuing smokers. . . . We calculated the weighted mean change for both groups, though formal statistical analysis was not possible to compare groups. . . . These data indicate little change in mental health from baseline to follow-up in continuing smokers, while smokers who quit showed reductions in adverse mental health symptoms and improvements in positive affect and quality of life.”

“This study illustrates the importance of providing tobacco-cessation treatment to individuals with behavioral health conditions, to help with both improvement in symptoms of mental illness and overall physical health,” Lori Raney, M.D., said in an interview with Psychiatric News. “Psychiatrists have an important role to play in assisting in this treatment and can provide guidance and support to patients and in helping our colleagues in other medical settings.” In addition to being medical director of Axis Health System in Durango, Colo., Raney has a special interest in smoking cessation and mental health.

The research was funded by the United Kingdom Center for Tobacco and Alcohol Studies.

This article first appeared on ‘Psychiatry Online’ on 15 April 2014.