It is the first trial to compare the increasingly popular "e-cigarette" -- a plastic tube which heats a liquid to an inhalable vapour -- against nicotine patches as an anti-smoking aid.
Researchers in Auckland, New Zealand, recruited 657 smokers who wanted to quit, and assigned them randomly to three groups.
Two groups of around 290 people were given a 13-week supply of either patches or e-cigarettes that delivered nicotine vapour.
Another 73 were given e-cigarettes without nicotine.
Six months later, the volunteers were then questioned, and their breath was analysed for carbon monoxide telltales of smoking, to rate their success in giving up tobacco.
The success rate among the nicotine e-cigarettes was 7.3 percent, compared with 5.8 percent in the patch group and 4.1 percent in the non-nicotine e-cigarette group.
None of the e-cigarette users fell ill from using the product, but the researchers stress that its long-term safety -- an issue that has emerged in the European Union which plans to class e-cigs as medicinal products -- remains unclear.
"E-cigarettes, with or without nicotine, were modestly effective at helping smokers to quit, with similar achievement of abstinence as with nicotine patches, and few adverse events," says the study, published by The Lancet.
But, it adds: "Uncertainty exists about the place of e-cigarettes in tobacco control, and more research is urgently needed to clearly establish their overall benefits and harms."
The probe, led by Chris Bullen at the University of Auckland, was presented this weekend at a conference of the European Respiratory Society in Barcelona, Spain, The Lancet said.