Smoking and mental health
Some health providers and people who smoke believe that smoking helps reduce stress and other mental health symptoms, like depression and anxiety. They worry that stopping smoking may make mental health symptoms worse. However, studies have shown that smoking may have a negative impact on people's mental health, and stopping smoking could reduce anxiety and depression.
Why we did this Cochrane Review
We wanted to find out how stopping smoking affects people's mental health. If stopping smoking improves mental health symptoms, rather than worsening them, then this may encourage more people to try to quit smoking and more health professionals to help their patients to quit. It may also discourage people from beginning to smoke tobacco in the first place.
What did we do?
We searched for studies that lasted for at least six weeks that included people who were smoking at the start of the studies. To be included, studies also had to measure whether people did or did not stop smoking and any changes in mental health during the study.
We were interested in how stopping smoking affected:
- symptoms of anxiety;
- symptoms of depression;
- symptoms of anxiety and depression together;
- symptoms of stress;
- overall well-being;
- mental health problems;
- social well-being, personal relationships, isolation and loneliness.
Search date: we included evidence published up to 7 January 2020.
What we found
We found 102 studies in more than 169,500 people: some studies did not clearly report how many people took part. The studies used a range of different assessment scales to measure people's mental health symptoms.
Most studies included people from the general population (53 studies); 23 studies included people with mental health conditions; other studies included people with physical or mental health conditions, or long-lasting physical conditions, who had recently had surgery, or who were pregnant.
We combined and compared the results from 63 studies that measured changes in mental health symptoms, and from 10 studies that measured how many people developed a mental health disorder during the study.
What are the results of our review?
Compared with people who continued to smoke, people who stopped smoking showed greater reductions in:
- anxiety (evidence from 3141 people in 15 studies);
- depression (7156 people in 34 studies); and
- mixed anxiety and depression (2829 people in 8 studies).
Our confidence in our results was very low (for depression), low (for anxiety), and moderate (for mixed anxiety and depression). Our confidence was reduced because we found limitations in the ways the studies were designed and carried out.
Compared with people who continued to smoke, people who stopped smoking showed greater improvements in:
- symptoms of stress (evidence from 4 studies in 1792 people);
- positive feelings (13 studies in 4880 people); and
- mental well-being (19 studies in 18,034 people).
There was also evidence that people who stopped smoking did not have a reduction in their social well-being, and their social well-being may have increased slightly (9 studies in 14,673 people).
In people who stopped smoking, new cases of mixed anxiety and depression were fewer than in those who continued to smoke (evidence from 3 studies in 8685 people). New cases of anxiety were also fewer (2 studies in 2293 people). We were unable to come to a decision about the numbers of new cases of depression, as the results from different studies were too variable.
People who stop smoking are not likely to experience a worsening in their mood long-term, whether they have a mental health condition or not. They may also experience improvements in their mental health, such as reductions in anxiety and depression symptoms.
Taken together, these data provide evidence that mental health does not worsen as a result of quitting smoking, and very low- to moderate-certainty evidence that smoking cessation is associated with small to moderate improvements in mental health. These improvements are seen in both unselected samples and in subpopulations, including people diagnosed with mental health conditions. Additional studies that use more advanced methods to overcome time-varying confounding would strengthen the evidence in this area.
There is a common perception that smoking generally helps people to manage stress, and may be a form of 'self-medication' in people with mental health conditions. However, there are biologically plausible reasons why smoking may worsen mental health through neuroadaptations arising from chronic smoking, leading to frequent nicotine withdrawal symptoms (e.g. anxiety, depression, irritability), in which case smoking cessation may help to improve rather than worsen mental health.
To examine the association between tobacco smoking cessation and change in mental health.
We searched the Cochrane Tobacco Addiction Group's Specialised Register, Cochrane Central Register of Controlled Trials, MEDLINE, Embase, PsycINFO, and the trial registries clinicaltrials.gov and the International Clinical Trials Registry Platform, from 14 April 2012 to 07 January 2020. These were updated searches of a previously-conducted non-Cochrane review where searches were conducted from database inception to 13 April 2012.
We included controlled before-after studies, including randomised controlled trials (RCTs) analysed by smoking status at follow-up, and longitudinal cohort studies. In order to be eligible for inclusion studies had to recruit adults who smoked tobacco, and assess whether they quit or continued smoking during the study. They also had to measure a mental health outcome at baseline and at least six weeks later.
We followed standard Cochrane methods for screening and data extraction. Our primary outcomes were change in depression symptoms, anxiety symptoms or mixed anxiety and depression symptoms between baseline and follow-up. Secondary outcomes included change in symptoms of stress, psychological quality of life, positive affect, and social impact or social quality of life, as well as new incidence of depression, anxiety, or mixed anxiety and depression disorders.
We assessed the risk of bias for the primary outcomes using a modified ROBINS-I tool. For change in mental health outcomes, we calculated the pooled standardised mean difference (SMD) and 95% confidence interval (95% CI) for the difference in change in mental health from baseline to follow-up between those who had quit smoking and those who had continued to smoke. For the incidence of psychological disorders, we calculated odds ratios (ORs) and 95% CIs. For all meta-analyses we used a generic inverse variance random-effects model and quantified statistical heterogeneity using I2. We conducted subgroup analyses to investigate any differences in associations between sub-populations, i.e. unselected people with mental illness, people with physical chronic diseases.
We assessed the certainty of evidence for our primary outcomes (depression, anxiety, and mixed depression and anxiety) and our secondary social impact outcome using the eight GRADE considerations relevant to non-randomised studies (risk of bias, inconsistency, imprecision, indirectness, publication bias, magnitude of the effect, the influence of all plausible residual confounding, the presence of a dose-response gradient).
We included 102 studies representing over 169,500 participants. Sixty-two of these were identified in the updated search for this review and 40 were included in the original version of the review. Sixty-three studies provided data on change in mental health, 10 were included in meta-analyses of incidence of mental health disorders, and 31 were synthesised narratively.
For all primary outcomes, smoking cessation was associated with an improvement in mental health symptoms compared with continuing to smoke: anxiety symptoms (SMD −0.28, 95% CI −0.43 to −0.13; 15 studies, 3141 participants; I2 = 69%; low-certainty evidence); depression symptoms: (SMD −0.30, 95% CI −0.39 to −0.21; 34 studies, 7156 participants; I2 = 69%' very low-certainty evidence); mixed anxiety and depression symptoms (SMD −0.31, 95% CI −0.40 to −0.22; 8 studies, 2829 participants; I2 = 0%; moderate certainty evidence). These findings were robust to preplanned sensitivity analyses, and subgroup analysis generally did not produce evidence of differences in the effect size among subpopulations or based on methodological characteristics. All studies were deemed to be at serious risk of bias due to possible time-varying confounding, and three studies measuring depression symptoms were judged to be at critical risk of bias overall. There was also some evidence of funnel plot asymmetry. For these reasons, we rated our certainty in the estimates for anxiety as low, for depression as very low, and for mixed anxiety and depression as moderate.
For the secondary outcomes, smoking cessation was associated with an improvement in symptoms of stress (SMD −0.19, 95% CI −0.34 to −0.04; 4 studies, 1792 participants; I2 = 50%), positive affect (SMD 0.22, 95% CI 0.11 to 0.33; 13 studies, 4880 participants; I2 = 75%), and psychological quality of life (SMD 0.11, 95% CI 0.06 to 0.16; 19 studies, 18,034 participants; I2 = 42%). There was also evidence that smoking cessation was not associated with a reduction in social quality of life, with the confidence interval incorporating the possibility of a small improvement (SMD 0.03, 95% CI 0.00 to 0.06; 9 studies, 14,673 participants; I2 = 0%). The incidence of new mixed anxiety and depression was lower in people who stopped smoking compared with those who continued (OR 0.76, 95% CI 0.66 to 0.86; 3 studies, 8685 participants; I2 = 57%), as was the incidence of anxiety disorder (OR 0.61, 95% CI 0.34 to 1.12; 2 studies, 2293 participants; I2 = 46%). We deemed it inappropriate to present a pooled estimate for the incidence of new cases of clinical depression, as there was high statistical heterogeneity (I2 = 87%).