Findings 657 people were randomised (289 to nicotine e-cigarettes, 295 to patches, and 73 to placebo e-cigarettes) and were included in the intention-to-treat analysis. At 6 months, verifi ed abstinence was 7·3% (21 of 289) with nicotine e-cigarettes, 5·8% (17 of 295) with patches, and 4·1% (three of 73) with placebo e-cigarettes (risk diff erence for nicotine e-cigarette vs patches 1·51 [95% CI –2·49 to 5·51]; for nicotine e-cigarettes vs placebo e-cigarettes 3·16 [95% CI –2·29 to 8·61]). Achievement of abstinence was substantially lower than we anticipated for the power calculation, thus we had insuffi cient statistical power to conclude superiority of nicotine e-cigarettes to patches or to placebo e-cigarettes. We identifi ed no signifi cant diff erences in adverse events, with 137 events in the nicotine e-cigarettes group, 119 events in the patches group, and 36 events in the placebo e-cigarettes group. We noted no evidence of an association between adverse events and study product. Interpretation E-cigarettes, with or without nicotine, were modestly eff ective at helping smokers to quit, with similar achievement of abstinence as with nicotine patches, and few adverse events. Uncertainty exists about the place of e-cigarettes in tobacco control, and more research is urgently needed to clearly establish their overall benefi ts and harms at both individual and population levels.