The study, published in Addiction, surveyed 5,863 smokers between 2009 and 2014 who had attempted to quit smoking without the aid of prescription medication or professional support. 20% of people trying to quit with the aid of e-cigarettes reported having stopped smoking conventional cigarettes at the time of the survey.
The research, chiefly funded by Cancer Research UK, suggests that e-cigarettes could play a positive role in reducing smoking rates. “E-cigarettes could substantially improve public health because of their widespread appeal and the huge health gains associated with stopping smoking,” says Professor Robert West of UCL’s Department of Epidemiology & Public Health, senior author of the study. “However, we should also recognise that the strongest evidence remains for use of the NHS stop-smoking services. These almost triple a smoker’s odds of successfully quitting compared with going it alone or relying on over-the-counter products.” 
Another survey by the same team found that most e-cigarette use involves first generation ‘cigalike’ products rather than second generation ones that use refillable cartridges and a wider choice of nicotine concentrations and flavours . Dr Jamie Brown of UCL’s Department of Clinical, Educational and Health Psychology, lead author of both reports, says: “We will continue to monitor success rates in people using e-cigarettes to stop smoking to see whether there are improvements as the devices become more advanced.”
Some e-cigarette users may want to continue using them indefinitely. “It is not clear whether long-term use of e-cigarettes carries health risks but from what is known about the contents of the vapour these will be much less than from smoking,” says Professor West.