Generally consistent with results from clinical trials, findings from this study show that use of varenicline, bupropion, or the nicotine patch is associated with increased quit rates compared to quit rates among those attempting to quit without medication. Among those for whom systematic recall bias was largely minimized, those who used any of these medications exhibited a 3-fold or greater increase in six-month continuous abstinence, with varenicline users experiencing a nearly 6-fold increase. Given the limited power, no clear conclusions can be drawn about oral NRT use, but any effects appear smaller than those found for the other products. Results also suggest that failure to control for differential recall of unsuccessful quit attempts between medication users and nonusers may explain the inconsistent results of previous population based studies; as we tightened control over recall effects, the size of the positive effects for medications increased and the effect for NRT patches became significant. Lastly, our sample resembles samples from previous population studies in that many smokers did not use medication when attempting to quit, and this was particularly true of younger smokers, minorities, those with low incomes, and those, understandably, who did not believe medications make quitting easier.
These findings should be interpreted in light of the following study limitations: reliance on self-reported smoking status (though it is unlikely that successful quitters in the real-world, who were neither compelled nor compensated to use medication, would misrepresent how they achieved cessation), no control over potential differences in motivation to quit or differences in relevant policy changes (e.g. increases in cigarette prices), the possibility that some subgroups of the population may have been underrepresented, absence of an assessment of medication side effects, and reduced sample sizes when analyses were restricted to recent quit attempters (which left insufficient power to detect cross-country differences in effectiveness, p >.05 for all country interaction terms).
Also, prior to wave 6, we could not ascertain whether medication was used specifically during a respondent’s last quit attempt, meaning that results presented in indicate estimated effect sizes for those known to have used medication at some point during the preceding year. However, beginning in wave 6, an additional item was added to the survey allowing for smoking cessation to be assessed as a direct function of medication use/non-use during the last quit attempt in particular, and analyses based on this subset of respondents (N = 1731) indicate that all recall bias-reduced estimates of medication effectiveness are higher when assessed as a direct function of respondents’ last quit attempts. We also further restricted these analyses to respondents whose quit attempt lasted for at least one day, in an effort to exclude short quit attempts that some might not consider to be serious, and found that although effectiveness estimates were somewhat attenuated, the conclusions drawn from these results were the same as those drawn from .
We carried out several additional analyses to assess the representativeness of our effectiveness findings, including: (1) performing analyses using longitudinally weighted data, which produced the same conclusions as those drawn from , (2) statistically comparing those who were lost to follow-up (~30%) with those who were retained in the sample in terms of demographic, smoking-related, and medication usage variables, and found these groups to be statistically indistinguishable on all variables, and (3) performing sensitivity analyses in which we supposed that all those who were lost to follow-up did not quit smoking, and though the effect sizes for nicotine patch effectiveness and varenicline effectiveness were somewhat attenuated, the conclusions drawn from these results were the same as those drawn from .
Balanced against the above study limitations are several strengths, including: (1) the large sample of smokers compared to some other studies; (2) the breadth of the sample (representative from four countries), (3) the cohort design, which allowed for longer term outcomes to be collected at subsequent survey waves, (4) use of generalized estimating equations, which allowed for repeat longitudinal analyses to be performed while accounting for repeated measurements within persons over time, and (5) measurement of time to recalled events, along with adjustment for numerous potential confounders of medication effectiveness.
The association between medication use and recall of failed quit attempts requires that population-based evaluations of medication effectiveness account for quit attempt recency.36
Indeed, results reported in the present study show that the estimated magnitude of effectiveness decreases with decreasing quit attempt recency. Reduction of recall bias can be achieved by using prospective cohorts and timely assessments, or by statistically controlling for time elapsed between events and measurement of events. Failure to address this bias may account for some of the previous inconsistencies observed in the literature; retrospective studies evaluating quit attempts occurring within one year of interview generally found NRT to be ineffective,17–21
while a study using assessments occurring every three months and a fully prospective study found NRT to be effective.23–24
Gilpin et al. (2006), using a retrospective design, did find a cessation benefit of NRT for smokers living in smoke-free homes, and suggested that NRT is more effective among those who are more motivated to quit.26
Although there was a suggestion that oral NRT users may experience higher continuous abstinence rates than nonusers, these rates were statistically indistinguishable from those of nonusers. Although our power to detect a significant effect was limited, it remains possible that there is no long term benefit of oral NRT when used in the population setting. We did find that over 80% of nicotine gum users reported using fewer than the recommended 8 pieces per day46
, as have other studies47–48
, and it remains plausible that insufficient use contributed to reduced effectiveness.
The bias-reduced estimates of varenicline, bupropion, and nicotine patch effectiveness shown in our study are somewhat higher than the clinical trial estimates of medication efficacy.1–4
This could be due to chance effects, but could plausibly be real; in real-life settings, we are testing the combined effect of the drug and nonspecific effects. To the extent that nonspecific effects accompany the drug (e.g. the belief that it will help), success rates should be greater than those estimated from RCTs. Thus, if our estimates are representative, more medication users are helped than many conventional estimates suggest.