BACKGROUND AND AIMS: Smokers quitting successfully with the help of e-cigarettes often continue vaping. It is not known whether this promotes or prevents relapse back to smoking. This study aimed to determine whether use of e-cigarettes after successful smoking cessation affects the probability of relapse later on.

DESIGN: Secondary analysis of a randomised controlled trial where participants received combination nicotine replacement therapy (NRT) or e-cigarettes to compare relapse rates in the two study arms and in abstainers who did and did not use e-cigarettes.

SETTING: Four stop-smoking services in the United Kingdom.

PARTICIPANTS: 886 smokers (median age 41, smoking on average 15 cigarettes per day, 48% female) seeking help with stopping smoking.

MEASUREMENTS: Main outcome was relapse to smoking by 12 months in participants who were abstinent at 4 weeks or at 6 months. Relapse was defined as abstinence at 4 weeks but not at one year or abstinence at 6 months but not at one year. Abstinence from smoking was defined as no smoking over the past 7 days. E-cigarette use was defined as using e-cigarettes at the time of abstinence on at least one day per week.

FINDINGS: Abstainers in the e-cigarette arm were less likely to relapse than abstainers in the NRT arm [relative risk (RR) = 0.78, 95% confidence interval (CI) = 0.64-0.96 for relapse between 4 weeks and 1 year; RR = 0.71, 95% CI = 0.55-0.93 for relapse between 6 months and 1 year). Relapse rates over both time periods were also lower in abstainers who used e-cigarettes compared with abstainers who did not use e-cigarettes (RR = 0.79, 95% CI = 0.65-0.97 and RR = 0.75, 95% CI = 0.57-0.98, respectively).

CONCLUSIONS: Use of e-cigarettes after stopping smoking is associated with a reduced risk of relapse.