The effect of smoking cessation interventions on socioeconomic inequalities in smoking: A Cochrane systematic review

Background
People from lower socioeconomic groups are more likely to smoke and less likely to successfully quit, making tobacco smoking a leading driver of health inequalities. We assessed whether effects of individual-level smoking cessation (SC) interventions differed by socioeconomic groups, and considered their potential impact on inequalities in smoking.
 
Methods
Systematic review and meta-analyses. We searched for RCTs on individual-level SC interventions compared to no treatment, placebo, or other SC intervention in adults. Studies must have assessed or reported SC rates, split by any measure of socioeconomic status at ≥6mths. We followed Cochrane methods and pooled ratios of ORs, where possible. We summarised all evidence in effect direction plots and categorised the intervention’s potential impact on inequalities in smoking.
 
Results 
We identified 77 completed studies, representing 127,791 randomised participants. We deemed 52 studies at high overall risk-of-bias. 
 
We found very low-certainty evidence for all the main pharmacological interventions compared to control. Evidence on cytisine (ROR 1.13, 95% CI 0.73 to 1.74; 1 study, 2472 participants) and nicotine electronic cigarettes (ROR 4.57, 95% CI 0.88 to 23.72; 1 study, 989 participants)) compared to control indicated a possibly positive impact on inequalities in smoking, with a greater relative effect of these interventions on quit rates in lower compared to higher SES groups.
 
We found a possibly negative impact of bupropion compared to control (ROR 0.05, 95% CI 0.00 to 1.00; from 1 of 2 studies, 354 participants; 1 study reported no difference)), and unclear or no evidence were available for NRT or varenicline, respectively. 
 
We found low-certainty evidence of a possibly-negative impact of print-based self-help (ROR 0.85, 95% CI 0.52 to 1.38; 3 studies, 4440 participants) and text-messaging (ROR 0.76, 95% CI 0.47 to 1.23; from 3 of 4 studies, 5339 participants; 1 study reported no difference), and very low-certainty evidence of a possibly-negative impact of financial incentives (ROR 0.91, 95% CI 0.45 to 1.85; from 5 of 6 studies, 3018 participants; 1 study reported no difference). Very low-certainty evidence indicated a possibly-neutral impact of face-to-face counselling (ROR 1.26, 95% CI 0.18, 8.93; from 1 of 6 studies, 294 participants; 5 studies reported no difference), and possibly-positive impact of telephone counselling (ROR 4.31, 95% CI 1.28 to 14.51; from 1 of 7 studies, 903 participants; 5 studies reported no difference, 1 unclear) and internet interventions (ROR 1.49, CI 0.99, 2.25; from 1/5 studies, 4613 participants; 4 studies reported no difference). 
 
Conclusion
Currently, there is no clear evidence to support the use of differential individual-level SC interventions for people from lower or higher SES groups, or that any one intervention would have an effect on inequalities in smoking. However, this conclusion may change as further data becomes available.