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People who quit smoking for at least 15 weeks may see improvements in their mental health, a secondary analysis of the EAGLES trial showed.

In adults with and without a psychiatric history, those who quit smoking for that duration saw reductions in Hospital Anxiety and Depression Scale (HADS) scores at 6 months compared with active smokers, reported Angela Difeng Wu, MSc, of the University of Oxford in England, and coauthors.

After adjustment for various factors, sustained smoking cessation was associated with a 0.40-point difference for anxiety (95% CI -0.58 to -0.22) and 0.47-point difference for depression (95% CI -0.61 to -0.33) on HADS -- a 0-21 scale where lower scores indicate better mental health.

Among participants who ceased smoking, those with a prior psychiatric disorder experienced larger reductions in scores for both anxiety (-0.48 vs -0.29 for quitters without such a history) and depression (-0.60 vs -0.32).

While a propensity score matched analysis found similar reductions, an instrumental variable analysis was "unable to confirm this," according to the findings in .

"Smoking cessation is associated with decreased morbidity risk and improved quality of life at any age, with our analysis adding to evidence that it improves mental well-being too," Wu and colleagues noted. "Smoking is the leading cause of preventable disease and death in the world, with one in every two people who continue smoking through life dying from a smoking-related disease."

The researchers noted that misconceptions surrounding smoking and its impact on mental health often stand in the way of quitting.

"Many people who smoke state that they want to quit, but many continue because they report that smoking helps relieve stress and offers other mental health benefits. These apparent benefits may be spurious," the study authors wrote. "Feelings of low mood, irritability, and anxiety can manifest shortly after finishing a cigarette when blood levels of nicotine drop, and these feelings are relieved by smoking another cigarette."

"Therefore, individuals may perceive that smoking relieves their psychological distress; however, this distress may have been caused by smoking withdrawal. The belief that cigarettes are calming is widespread, and some health professionals may deter people with mental health disorders from trying to stop smoking," they added.

As of 2021, approximately 28 million U.S. adults smoke cigarettes, with in individuals with severe mental health struggles. Anywhere from 30-50% of smokers , but only about 7.5% manage to succeed.

"The disparity between smoking cessation rates in people with and without psychiatric disorders is concerning, given that smoking may account for up to two-thirds of the difference in life expectancy between people with a history of psychiatric disorders who smoke vs people who have never smoked," Wu's group wrote.

The present analysis was based on EAGLES (Evaluating Adverse Events in a Global Smoking Cessation Study), a safety study that from 2011 to 2015 randomized 8,144 participants across more than a dozen countries to either varenicline (Chantix), bupropion (Wellbutrin), nicotine patch, or placebo. Individuals enrolled smoked at least 10 cigarettes a day over the prior year but were motivated to quit.

The were that smoking cessation with either varenicline or bupropion led to no increased risk of moderate or severe neuropsychiatric adverse events when compared with nicotine patch or placebo, with individuals assigned to varenicline achieving higher smoking abstinence rates.

For the current analysis from Wu's group, only the 4,260 U.S. participants from EAGLES were included due to data sharing agreements. Of those participants, the mean age was 46.5 years, 58.3% were women, 71.5% were white, and 25% were Black. A majority (55.4%) had a history of mental illness, and 21.7% had been prescribed psychotropic medication. (Individuals with current mental illness, as well as those at high risk for suicide, were excluded from the trial.)

Average HADS scores for participants at baseline were 4.25 for anxiety and 2.44 for depression. Scores were higher among those with a psychiatric history and lower among those who ultimately quit. While patients were evenly randomized across the four study groups, a higher proportion of quitters came from the varenicline group (36%).

Limitations included instances of missing data, loss to follow-up, and that the reductions in HADS scores were "less than the minimally clinically important differences suggested by populations with chronic obstructive pulmonary disease and [cardiovascular disease]," wrote Wu and colleagues.

Also, despite EAGLES being the largest smoking cessation study, the researchers suggested that the results of the instrumental variable analysis -- which showed non-significant increases for both depression and anxiety -- were underpowered.

Moreover, they noted that any participant who didn't meet the smoking cessation standard of 15 weeks were still categorized as continued smokers, which limits further understanding of the association between mental health and smoking cessation.

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