Gemma MJ Taylor, Amy E Taylor, Kyla H Thomas, Tim Jones, Richard M Martin, Marcus R Munafò and Neil M Davies
Tobacco is the world’s leading cause of premature disease and death. One in two smokers will die from their addiction unless they quit. Smoking is also a major contributor to health inequalities between the richest and poorest in society. Evidence from the Health Improvement Network in the United Kingdom indicates that smokers from more deprived groups are just as likely as those from less deprived groups to receive advice to quit from their GP. However, evidence from observational studies suggests that smokers from disadvantaged backgrounds are much less likely to quit, even after accessing treatment from specialist stop-smoking services.
We know from clinical trials that varenicline, a smoking cessation drug available via NHS prescription in the UK, is efficacious in helping smokers to quit for up to 12 months. However, the follow-up in trials is very short, and the participants may not be representative of patients seen in general practice. We used data from the UK Clinical Practice Research Database (CPRD) to determine if varenicline is effective in everyday clinical settings up to 4 years after prescription, and to see if socioeconomic position alters varenicline’s effect on smoking cessation.
As reports of adverse side effects suggest that patients prescribed varenicline are generally much healthier than those prescribed nicotine replacement therapies (e.g. nicotine patches or inhalers), we were concerned that multivariable adjusted regression may suffer from residual confounding. To overcome this, we applied propensity score matching and instrumental variable methods. We triangulated across analytical approaches to determine if the long-term effects of varenicline on smoking cessation were likely to be causal.
In our recently published study, we found that patients prescribed varenicline as part of routine primary care were more likely to successfully quit smoking for up to 4 years after treatment than those prescribed nicotine replacement therapies. We found little evidence that varenicline’s effectiveness differed by socioeconomic position.
Our study is the largest to date to investigate the effectiveness of varenicline, and included 220 136 primary care patients from the CPRD with up to 4 years of follow-up. Our results complement those recently reported from the EAGLES randomised trial, which suggested that after 9 to 24 weeks, varenicline improved cessation rates (odds ratio, 1.52; 95% CI, 1.29–1.78). In comparison, our multivariable logistic regression analysis produced an odds ratio of 1.46 (95% CI, 1.42–1.50) at 6-month follow-up. We compare our results with those from the EAGLES trial, along with results from Baker and colleagues recently published in JAMA, and others, in our study.
In our analysis of the CPRD, we found that smokers from the most deprived areas were less likely to be prescribed varenicline, but we found little evidence of even very small differences in the effect of varenicline by socioeconomic position.
The results from our study provide new evidence that varenicline is not only efficacious (as indicated by trials) but is also effective in real-world clinical practice. Taken together, this evidence may be used to update clinical guidelines on the use of varenicline for smoking cessation to ensure that smokers from all backgrounds are offered the best treatments available to help them quit smoking.
Taylor GMJ, Taylor AE, Thomas KH, et al. The effectiveness of varenicline versus nicotine replacement therapy on long-term smoking cessation in primary care: a prospective cohort study of electronic medical records. International Journal of Epidemiology 2017. doi: https://doi.org/10.1093/ije/dyx109.
Gemma Taylor is a Cancer Research UK Research Fellow based at the Tobacco and Alcohol Research Group at the University of Bristol, and is part of the MRC’s Integrative Epidemiology Unit. Amy Taylor is a Senior Research Associate based at the Tobacco and Alcohol Research Group at the University of Bristol, and is part of the MRC’s Integrative Epidemiology Unit. Kyla Thomas is a Clinical Lecturer in Public Health at the School of Social and Community Medicine, University of Bristol, and a Consultant in Public Health at South Gloucestershire Council. Tim Jones is a Senior Research Associate in Epidemiology/Knowledge Transfer at the School of Social and Community Medicine, University of Bristol. Richard Martin is a Professor of Clinical Epidemiology at the School of Social and Community Medicine, University of Bristol. Marcus Munafò is a Professor of Biological Psychology and director of the Tobacco and Alcohol Research Group at the University of Bristol, and is part of the MRC’s Integrative Epidemiology Unit. Neil Davies is a Research Fellow in the School of Social and Community Medicine, University of Bristol, and is part of the MRC’s Integrative Epidemiology Unit.