Introduction: Trial evidence suggest that e-cigarettes may aid in quitting smoking, while observational studies have found conflicting results. However, many observational studies have not adjusted for important differences between e-cigarette users and non-users.
Methods: We aimed to determine the association between e-cigarette use frequency and motivation to use e-cigarettes to quit smoking, and smoking cessation using data from Canada's largest smoking cessation program. Participants who completed a baseline assessment and 6-month follow-up questionnaire were divided post hoc into 4 groups based on their self-reported e-cigarette use during the 30 days before baseline: 1) non-users; 2) users of e-cigarettes not containing nicotine; 3) occasional users; and 4) frequent users. Occasional and frequent users were further divided into two groups based on whether they reported using e-cigarettes to quit smoking. Abstinence at 6-month follow-up (7-day point prevalence abstinence) was compared among groups.
Results: Adjusted quit probabilities were significantly higher (both p<0.001) for frequent baseline e-cigarette users (31.6%; 95% CI = 29.3%, 33.8%) than for non-users (25.8%; 25.3%, 26.3%) or occasional users (24.2%; 22.5%, 26.0%). Unadjusted proportions favoured non-users over occasional users (p<0.001), but this was not significant after adjustment (p=0.06). People using e-cigarettes to quit smoking were not likelier than other users to be successful, but were likelier to report frequent e-cigarette use during follow-up.
Conclusions: Frequent baseline e-cigarette use predicted successful smoking cessation, compared to occasional and non-users. Use of e-cigarettes to quit did not predict smoking cessation, but was associated with continued use during follow-up, perhaps due in part to planned transitions to e-cigarettes.
Implications: Prior observational studies investigating e-cigarettes use for smoking cessation have found that occasional users have poorer outcomes than either frequent or non-users. Consistent with these studies, occasional users in our data also had poorer outcomes. However, after adjustment for variables associated with cessation success we found that cessation probabilities did not differ between occasional and non-users. These findings are consistent with trial data showing a benefit of e-cigarette use among people trying to quit smoking. Results of this study suggest that differences between trials and previous observational studies may be due to unaddressed confounding in the latter.
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