E-cigarettes are almost twice as effective as nicotine replacements that help smoke leave, the study says.
The study showed that 18% of smokers who used them stopped smoking after a year, compared with 9.9% of those taking nicotine replacement medicines.
A study of 886 smokers is the first to test how effective modern e-cigarettes are to end.
Scientists hope their findings will lead to the availability of standard smoking cessation services.
Public health of England has already asked for electronic cigarettes to be released in the NHS within five years, suggesting that there are studies that are at least 95% less harmful than cigarettes.
So far, however, there has been little evidence of how effective they are as tools for permanent smoking.
Leading researcher prof. Peter Hajek from Queen Mary University of London said: "Although many smokers say smoking successfully ended with electronic cigarettes, healthcare professionals are reluctant to recommend their use due to lack of clear evidence from randomized controlled trials.
"Now it's likely to change."
Accelerate "reduction in smoking
Study participants who were addicted to smoking and had not given up before, attended NHS smoking cessation services and were randomly assigned to two groups:
- to those who received substitution treatment for nicotine of their choice, including gum, patches, lozenges, sprays and inhalants, or a combination of treatment for up to three months
- those who received an e-cigarette starter pack with one or two e-liquid vials (two to four weeks)
Those who received electronic cigarettes were encouraged to buy future supplies of their own strength and flavor, and all participants received weekly individual behavioral support for at least four weeks.
The study, published in the New England Journal of Medicine, found that, in addition to having a higher exit rate, more electronic cigarette users reduced their smoking by at least 50%.
E-cigarettes also provided greater satisfaction and were rated more useful than nicotine replacement therapy.
A higher proportion of those who used the device experienced mouth and throat irritation (65% in 51%), although people taking nicotine replacement medications reported more frequent nausea (38% in 31%). These effects were mostly mild.
Professor Hajek said he hopes the results of the study will put an end to smoking that offers e-cigarette starter pack users and guidelines on how to avoid paying for their own supplies.
"This may eventually accelerate the reduction of smoking and smoking," said Dunja Przulj, another author of the study from Queen Mary University in London.
The study has some limitations.
Because people knew what treatment they were receiving – unlike they were "blinded" because they were in most randomized controlled trials – it was possible for participants to perceive nicotine replacement as a minor alternative and less effort to stop treatment, said the authors .
They also said that more work is needed to see if their outcomes will apply to countries outside the United Kingdom and less dependent smokers.
The study comes from an independent review of evidence on electronic cigarettes published last February in public health in England. It has been found that there is "overwhelming evidence" that they are much safer than smoking and "negligible risk to the standing person".
Some experts, however, said that e-cigarettes, although safer than regular cigarettes, are not without damage and their long-term effects are not yet known.
Responding to this latest research, Public Health England said: "All smoking cessation services should welcome smokers who want to stop using an electronic cigarette."