Quitting smoking has been found to improve mental health, illuminating another benefit of kicking the habit that kills nearly 500,000 Americans each year.

Dr. Patricia A. Cavazos-Regh, a professor of psychiatry at Washington University School of Medicine and lead author of the new study, said in a press release that the findings also provide an incentive for therapists to retire the long-held belief that smoking should be tackled after rehabilitation. “Clinicians tend to treat the depression, alcohol dependence, or drug problem first and allow patients to ‘self-medicate’ with cigarettes if necessary,” she said. “The assumption is that psychiatric problems are more challenging to treat and that quitting smoking may interfere with treatment.”

But the new study, which is published in the journal Psychological Medicine, shows that quitting smoking may actually make such rehabilitation programs more effective by boosting mental health. Cutting down or quitting completely were both associated with a significantly lower risk of mood disorders as well as alcohol and drug problems. “We don’t know if their mental health improves first and then they are more motivated to quit smoking or if quitting smoking leads to an improvement in mental health,” Cavazos-Rehg explained. “But either way, our findings show a strong link between quitting and a better psychiatric outlook.”

For the study, Cavazos-Rehg and colleagues looked at questionnaires from the National Epidemiologic Survey on Alcohol and Related Conditions — a project from 2000 that surveyed 35,000 people on their psychiatric profiles as well as their drinking and smoking habits. The project consisted of two interviews conducted two years apart. By comparing the results, the team was able to analyze the relationship between smoking and mental health.

They found that those who reported psychiatric issues or substance abuse during the first interview were significantly less likely to report them again at the second interview if they had quit smoking in the intervening years. Similarly, those who did not report any issues at the first interview were less likely to have developed them by the second interview if they were no longer smoking.

Quitting Smoking and Mental Health

Official estimates indicate that smoking and secondhand smoke is currently the direct cause of over 480,000 deaths in the U.S. About half of all smokers now die from emphysema, cancer, or other medical complications arising from the habit. According to the Centers for Disease Control and Prevention, tobacco use costs the nation about $298 billion each year.

In an email to Medical Daily, Cavazos-Regh explained that the findings align with previous results implicating smoking in psychiatric ills. By kicking the habit, smokers may simply save avoid complications they would otherwise develop. “Increasing evidence suggests that smoking leads to adverse mental health effects,” she wrote. “For example, human studies and animal models have linked smoking to increased depression, anxiety, and substance use disorders; this suggests that smoking cessation could prompt a remission of a psychiatric illness.”

That said, the correlation could also go the other way. “Or, it might be that individuals who have better control of their psychiatric illness are encouraged to subsequently quit smoking,” she added. “While causation can go in both directions, smokers can be more compelled to quit with new knowledge that positive behavioral and psychological outcomes can accompany smoking cessation.”