The trial, which involved almost 900 smokers who also received additional behavioural support, found that 18 per cent of e-cigarette users were smoke-free after a year, compared to 9.9 per cent of participants who were using other nicotine replacement therapies.
"This is the first trial to test the efficacy of modern e-cigarettes in helping smokers quit. E-cigarettes were almost twice as effective as the 'gold standard' combination of nicotine replacement products," said lead researcher Peter Hajek, Professor at Queen Mary University of London.
"Although a large number of smokers report that they have quit smoking successfully with the help of e-cigarettes, health professionals have been reluctant to recommend their use because of the lack of clear evidence from randomised controlled trials. This is now likely to change," Hajek added.
The new study, which was set-up to test the long-term efficacy of newer refillable e-cigarettes compared with a range of nicotine replacement treatments, was conducted among 886 smokers who attended UK National Health Service stop smoking services.
In addition to e-cigarettes being almost twice as effective, the researchers found that e-cigarette participants reported greater decline in incidence of cough and phlegm production after 52 weeks.
But e-cigarette participants reported more throat/mouth irritation (65.4 per cent vs 50.8 per cent) and nicotine replacement participants reported more nausea (37.8 per cent vs 31.4 per cent), the results showed.
"This is the first study to show the effectiveness of e-cigarettes combined with behavioural support for giving up smoking, and the results are extremely positive," said Sophia Lowes of Britain-based charity Cancer Research UK.