Duration of Nicotine Replacement Use and Smoking Cessation
In the present study, we found that the majority of smokers (≥72%) in the general population did not use any NRT when making an attempt to quit smoking. When using NRT to quit, the majority (86%) used it for less than the recommended duration of 8–12 weeks. NRT users smoked more cigarettes per day and had tried to quit more often in the past compared with persons who did not use NRT. There was no overall association between NRT use and quitting when duration of use was not taken into account. When duration of NRT use was considered, we found that persons who used NRT for less than 4 weeks were less likely to quit (adjusted OR = 0.51, P < 0.0001), whereas those who used NRT for longer (≥4 weeks) were more likely to quit. This finding helps to explain the null findings of some previous studies that did not include such detailed data on duration of use.
Findings of the suboptimal prevalence and duration of NRT use in the present study are consistent with those from other studies. For example, only 20%–23% of recent quitters reported having used NRT in their attempts to quit in a study in Massachusetts, and in other studies in the United States, 20%–32% of smokers who attempted to quit used medication. The median duration of NRT use was 14 days among smokers who attempted to quit in a study from California. These population-based studies help us understand what cessation methods smokers use and how they use cessation medication when making an attempt to quit in the general population. They might also explain why NRT has not been consistently associated with a higher likelihood of cessation in the general population (i.e., inadequate and underuse of NRT).
In the present study, we found that smokers who chose to use NRT were those who would be expected to have worse outcomes; that is, these smokers were more dependent or had trouble quitting in the past. Almost all crude odds ratios were smaller than the adjusted odds ratios, indicating that NRT users were more addicted to smoking than were persons who did not use, because when we did not control for tobacco-dependence variables (daily smoking status, number of cigarettes per day smoked, and self-perceived addiction), the odds ratios after adjustment for other variables were only slightly larger than the crude odds ratios (data not shown). This finding is similar to those from other nonrandomized studies, which suggests that a lack of or a negative association between NRT and smoking cessation reported in population studies might be due to inadequate control of confounding.
We also found that persons who used NRT (patch or gum) for less than 4 weeks had a lower odds of quitting compared with those who did not use NRT. Those who used NRT for less than 4 weeks were more addicted to tobacco compared with those who did not use NRT and those who used NRT for 4 or more weeks. Although we controlled for several factors related to addiction, residual confounding might still exist. These smokers might also have comorbid conditions (e.g., mental health or alcohol problems), as shown in other studies. Unfortunately, information on comorbid conditions was not collected in the Ontario Tobacco Survey.
To our knowledge, this is the first population-based longitudinal study using a representative sample of smokers in which the association between duration of NRT use and smoking cessation (≥1 month) was examined. There appeared to be a threshold association (4.0–7.9 weeks of NRT use resulted in double the odds of quitting) and a ceiling association (using NRT for the recommended duration of 8–12 weeks resulted in almost quadruple the odds of quitting) with quitting for 1 month or longer. Using NRT for 12 or more weeks was associated with 2.8 times higher odds of quitting, which was lower than that for using NRT for 8.0–11.9 weeks. These associations were mainly from using a nicotine patch; using a nicotine patch for the recommended duration was associated with even higher odds (5.9 times higher) of quitting. With regard to the duration of nicotine gum use, the threshold seemed to be the recommended duration (8–12 weeks) and beyond. A ceiling association could not be determined for nicotine gum use because the odds of quitting after using gum for 12 or more weeks were very similar to that for using gum between 8.0–11.9 weeks, and the sample size of persons who used gum for 16 or more weeks was too small.
The findings of the present study uniquely support the recommendation to use NRT for 8–12 weeks in the clinical practice guideline by the US Public Health Service, which reflects efficacious clinical treatments for tobacco dependence. Our findings are consistent with those from a large clinical trial (n = 2,861) and a medium-sized trial (n = 568) included in the 2012 Cochrane review on NRT for smoking cessation in which investigators found no difference in cessation rates when comparing nicotine patch use for 28 weeks with use for 12 weeks in the large trial and use for 24 weeks with use for 8 weeks in the medium-sized trial. These suggest the ceiling association of 8–12 weeks of NRT or nicotine patch use on smoking cessation.
The strengths of the present study included the population-based longitudinal study design, a relatively large representative sample of smokers, use of generalized estimating equations methods for analysis, the relatively short time period from one wave to the next (6 months), and the ability to control for many covariates, especially time-varying covariates. Using a representative sample allowed the study findings to be generalizable to the general population and provided specific evidence of the effectiveness of NRT because real-life situations were reflected.
A potential source of bias was the reliance upon self-reported cessation status. Because of the social undesirability of smoking, some participants might have misreported their smoking status (smokers who identified as quitters). However, an expert scientific review on biochemical verification has found that there is little reason to expect differential misrepresentation rates between biochemical validation and self-reported smoking status in most smoking cessation studies because the levels of misrepresentation are generally low (0%–8.8%). A recent study using representative data for the Canadian population showed no significant difference between national estimates of smoking prevalence based on self-report and those based on urinary cotinine concentration (smoking prevalence based on self-report was 0.3 percentage points lower than that based on urinary cotinine concentration).
In the present study, there might have been some measurement error for NRT use and quitting outcomes when smokers were asked to recall NRT use and smoking behaviors in the previous 6 months at each follow-up interview. In a recent population-based study, Borland et al. reported better recall of attempts to quit among smokers who use cessation medication than among self-quitters. If this difference in recall was present in our study, it would have had the effect of biasing the assessed associations between use of cessation medication and cessation outcomes toward the null. Thus, if this recall bias could be corrected, the observed association would be even stronger. It was not clear if nonconcurrent use of multiple forms of NRT was consecutive or separate, which might be a limitation. However, findings of any NRT use and nicotine patch use were very similar, bearing in mind that NRT might consist of multiple forms of medication but a nicotine patch is just one form of NRT.
Loss to follow-up had the potential to threaten the validity of the present findings. However, smokers with partial data (e.g., persons who were current smokers at wave 1, attempted to quit at wave 2, and lost to follow-up at wave 3) were included in the analysis. The proportion of complete loss to follow-up was small (10%), and loss to follow-up was not associated with smoking behaviors. Therefore, the findings of the present study were likely not affected by loss to follow-up.
It is possible that duration of NRT use itself might be a proxy for smoking abstinence. This means that if a smoker used NRT for more than 4 weeks, the smoker likely would not have been smoking for those 4 weeks (reverse association). If smokers stopped using NRT early because they felt, for example, that it was "too expensive" or "not safe" as opposed to "not working," the findings of the present study would be strengthened. Unfortunately, information on reasons for stopping use of NRT was not collected in the Ontario Tobacco Survey. If the reverse association were true, the association between duration of NRT use and quitting would increase with higher duration of NRT use. However, among those who used NRT for 4 weeks or longer, the rate of quitting was higher among smokers who used NRT 8.0–11.9 weeks (42%) than among those using NRT for 4.0–7.9 weeks (30%) or for ≥12 weeks (28%). Furthermore, among smokers who used NRT for 4 weeks or longer, the majority (67%) did not quit smoking for at least 1 month, indicating that duration of NRT use is not perfectly associated with duration of abstinence. Nevertheless, the present study cannot prove the causal relationship between duration of NRT use and smoking cessation. Future research is needed to confirm whether the association between duration of NRT use and smoking cessation is causal.
Another limitation was the lack of information on NRT dosage in the current study, which might explain the lower odds ratios for nicotine gum use. Prior research has shown that lower dosing of nicotine gum is common. Future studies might consider including dosage information to better understand the role of dosage. Information on comorbid conditions (depression and mental health) should be collected in future studies to more fully control for possible confounders.
Our study finds that using NRT for at least 4 weeks, especially using the patch for the recommended duration (8–12 weeks), is associated with a higher likelihood of quitting in the general population. However, the majority of smokers in the general population does not use NRT or uses it much less than the recommended duration when making an attempt to quit. Smokers should be encouraged to use NRT for the recommended duration to achieve better quitting outcomes.
Discussion
In the present study, we found that the majority of smokers (≥72%) in the general population did not use any NRT when making an attempt to quit smoking. When using NRT to quit, the majority (86%) used it for less than the recommended duration of 8–12 weeks. NRT users smoked more cigarettes per day and had tried to quit more often in the past compared with persons who did not use NRT. There was no overall association between NRT use and quitting when duration of use was not taken into account. When duration of NRT use was considered, we found that persons who used NRT for less than 4 weeks were less likely to quit (adjusted OR = 0.51, P < 0.0001), whereas those who used NRT for longer (≥4 weeks) were more likely to quit. This finding helps to explain the null findings of some previous studies that did not include such detailed data on duration of use.
Findings of the suboptimal prevalence and duration of NRT use in the present study are consistent with those from other studies. For example, only 20%–23% of recent quitters reported having used NRT in their attempts to quit in a study in Massachusetts, and in other studies in the United States, 20%–32% of smokers who attempted to quit used medication. The median duration of NRT use was 14 days among smokers who attempted to quit in a study from California. These population-based studies help us understand what cessation methods smokers use and how they use cessation medication when making an attempt to quit in the general population. They might also explain why NRT has not been consistently associated with a higher likelihood of cessation in the general population (i.e., inadequate and underuse of NRT).
In the present study, we found that smokers who chose to use NRT were those who would be expected to have worse outcomes; that is, these smokers were more dependent or had trouble quitting in the past. Almost all crude odds ratios were smaller than the adjusted odds ratios, indicating that NRT users were more addicted to smoking than were persons who did not use, because when we did not control for tobacco-dependence variables (daily smoking status, number of cigarettes per day smoked, and self-perceived addiction), the odds ratios after adjustment for other variables were only slightly larger than the crude odds ratios (data not shown). This finding is similar to those from other nonrandomized studies, which suggests that a lack of or a negative association between NRT and smoking cessation reported in population studies might be due to inadequate control of confounding.
We also found that persons who used NRT (patch or gum) for less than 4 weeks had a lower odds of quitting compared with those who did not use NRT. Those who used NRT for less than 4 weeks were more addicted to tobacco compared with those who did not use NRT and those who used NRT for 4 or more weeks. Although we controlled for several factors related to addiction, residual confounding might still exist. These smokers might also have comorbid conditions (e.g., mental health or alcohol problems), as shown in other studies. Unfortunately, information on comorbid conditions was not collected in the Ontario Tobacco Survey.
To our knowledge, this is the first population-based longitudinal study using a representative sample of smokers in which the association between duration of NRT use and smoking cessation (≥1 month) was examined. There appeared to be a threshold association (4.0–7.9 weeks of NRT use resulted in double the odds of quitting) and a ceiling association (using NRT for the recommended duration of 8–12 weeks resulted in almost quadruple the odds of quitting) with quitting for 1 month or longer. Using NRT for 12 or more weeks was associated with 2.8 times higher odds of quitting, which was lower than that for using NRT for 8.0–11.9 weeks. These associations were mainly from using a nicotine patch; using a nicotine patch for the recommended duration was associated with even higher odds (5.9 times higher) of quitting. With regard to the duration of nicotine gum use, the threshold seemed to be the recommended duration (8–12 weeks) and beyond. A ceiling association could not be determined for nicotine gum use because the odds of quitting after using gum for 12 or more weeks were very similar to that for using gum between 8.0–11.9 weeks, and the sample size of persons who used gum for 16 or more weeks was too small.
The findings of the present study uniquely support the recommendation to use NRT for 8–12 weeks in the clinical practice guideline by the US Public Health Service, which reflects efficacious clinical treatments for tobacco dependence. Our findings are consistent with those from a large clinical trial (n = 2,861) and a medium-sized trial (n = 568) included in the 2012 Cochrane review on NRT for smoking cessation in which investigators found no difference in cessation rates when comparing nicotine patch use for 28 weeks with use for 12 weeks in the large trial and use for 24 weeks with use for 8 weeks in the medium-sized trial. These suggest the ceiling association of 8–12 weeks of NRT or nicotine patch use on smoking cessation.
Strengths and Limitations
The strengths of the present study included the population-based longitudinal study design, a relatively large representative sample of smokers, use of generalized estimating equations methods for analysis, the relatively short time period from one wave to the next (6 months), and the ability to control for many covariates, especially time-varying covariates. Using a representative sample allowed the study findings to be generalizable to the general population and provided specific evidence of the effectiveness of NRT because real-life situations were reflected.
A potential source of bias was the reliance upon self-reported cessation status. Because of the social undesirability of smoking, some participants might have misreported their smoking status (smokers who identified as quitters). However, an expert scientific review on biochemical verification has found that there is little reason to expect differential misrepresentation rates between biochemical validation and self-reported smoking status in most smoking cessation studies because the levels of misrepresentation are generally low (0%–8.8%). A recent study using representative data for the Canadian population showed no significant difference between national estimates of smoking prevalence based on self-report and those based on urinary cotinine concentration (smoking prevalence based on self-report was 0.3 percentage points lower than that based on urinary cotinine concentration).
In the present study, there might have been some measurement error for NRT use and quitting outcomes when smokers were asked to recall NRT use and smoking behaviors in the previous 6 months at each follow-up interview. In a recent population-based study, Borland et al. reported better recall of attempts to quit among smokers who use cessation medication than among self-quitters. If this difference in recall was present in our study, it would have had the effect of biasing the assessed associations between use of cessation medication and cessation outcomes toward the null. Thus, if this recall bias could be corrected, the observed association would be even stronger. It was not clear if nonconcurrent use of multiple forms of NRT was consecutive or separate, which might be a limitation. However, findings of any NRT use and nicotine patch use were very similar, bearing in mind that NRT might consist of multiple forms of medication but a nicotine patch is just one form of NRT.
Loss to follow-up had the potential to threaten the validity of the present findings. However, smokers with partial data (e.g., persons who were current smokers at wave 1, attempted to quit at wave 2, and lost to follow-up at wave 3) were included in the analysis. The proportion of complete loss to follow-up was small (10%), and loss to follow-up was not associated with smoking behaviors. Therefore, the findings of the present study were likely not affected by loss to follow-up.
It is possible that duration of NRT use itself might be a proxy for smoking abstinence. This means that if a smoker used NRT for more than 4 weeks, the smoker likely would not have been smoking for those 4 weeks (reverse association). If smokers stopped using NRT early because they felt, for example, that it was "too expensive" or "not safe" as opposed to "not working," the findings of the present study would be strengthened. Unfortunately, information on reasons for stopping use of NRT was not collected in the Ontario Tobacco Survey. If the reverse association were true, the association between duration of NRT use and quitting would increase with higher duration of NRT use. However, among those who used NRT for 4 weeks or longer, the rate of quitting was higher among smokers who used NRT 8.0–11.9 weeks (42%) than among those using NRT for 4.0–7.9 weeks (30%) or for ≥12 weeks (28%). Furthermore, among smokers who used NRT for 4 weeks or longer, the majority (67%) did not quit smoking for at least 1 month, indicating that duration of NRT use is not perfectly associated with duration of abstinence. Nevertheless, the present study cannot prove the causal relationship between duration of NRT use and smoking cessation. Future research is needed to confirm whether the association between duration of NRT use and smoking cessation is causal.
Another limitation was the lack of information on NRT dosage in the current study, which might explain the lower odds ratios for nicotine gum use. Prior research has shown that lower dosing of nicotine gum is common. Future studies might consider including dosage information to better understand the role of dosage. Information on comorbid conditions (depression and mental health) should be collected in future studies to more fully control for possible confounders.
Conclusion
Our study finds that using NRT for at least 4 weeks, especially using the patch for the recommended duration (8–12 weeks), is associated with a higher likelihood of quitting in the general population. However, the majority of smokers in the general population does not use NRT or uses it much less than the recommended duration when making an attempt to quit. Smokers should be encouraged to use NRT for the recommended duration to achieve better quitting outcomes.
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