In a recent issue of Addiction, Langley et al. reported data on the effects of the introduction of varenicline on trends in prescribing of smoking cessation medications in England . Varenicline had been introduced as a new aid for smoking cessation in the United Kingdom in December 2006, and the National Institute for Health and Clinical Excellence had published guidance related to its use in July 2007 . To analyse whether varenicline had an impact on recent trends in prescribing of smoking cessation medications, Langley et al. carried out an analysis based on routinely collected data from a UK primary care database: The Health Improvement Network (THIN). Their outcome measures were the monthly rates of general practitioner (GP) prescribing of nicotine replacement therapy (NRT), bupropion and varenicline between June 2000 and June 2009. The authors concluded that varenicline did not ‘appear to have increased overall rates of prescribing for smoking cessation medication’ and that it ‘may not have led to a greater proportion of smokers being prescribed medication to help them stop smoking’.
An important limitation of the Langley et al. study is that their analysis could not dissociate the rate of usage of medications and the rate of attempts to quit smoking. The denominator in their analysis was the total number of patients from the THIN database, not the number of smokers attempting to quit (which would be the ‘population at risk’ of using smoking cessation medications). The authors acknowledged that smoking prevalence decreased during the study period, which ‘may in turn have resulted in a smaller pool of smokers trying to make quit attempts’, but found this decrease ‘to have had a negligible effect on the monthly rates of prescribing estimated in this study, and are thus unlikely to have biased the results’.
The measurement bias in the study by Langley et al. may be larger than they thought. We also investigated the impact of the introduction of varenicline on usage of smoking cessation medications, but used data from an English national household survey, the Smoking Toolkit Study, which was particularly designed to monitor smoking and quitting in the population . We estimated the rate of usage in smokers attempting to quit in the past 3 months prior to the month of the survey . During our study period, from November 2006 to December 2009, we found a significant linear decline in the percentage of smokers attempting to quit from about 18% to 15% (P < 0.001). Thus, the ‘population at risk’ of using smoking cessation medications decreased in recent years, which is likely to have resulted in an underestimation of medication usage in the Langley et al. study.
We concluded from our study that the introduction of varenicline did not appear to have substituted for the use of other prescription medication . Similar to Langley et al., we found that varenicline had become the second most commonly prescribed smoking cessation medication. The rate of use of NRT on prescription in smokers attempting to quit increased significantly during the period of our study, whereas use of NRT over-the-counter significantly decreased. The latter, however, is likely to have been due to other factors than the introduction of varenicline.