One in ten e-cigarette users stopped smoking within a year.
Nicotine free e-cigarettes helped just 4% give up smoking, studies showed.
A combination of randomised controlled trials (RCTs) and cohort studies, between 2004 and July 2014, were analysed by a team of researchers from the Cochrane Collection.
Of those who had not stopped smoking, 36% had halved the number of tobacco cigarettes they were smoking compared with 28% of people who used placebos in the trials.
Professor of Clinical Psychology, Peter Hajek, said: "Although our confidence in the effects of electronic cigarettes as smoking cessation interventions is limited because of the small number of trials, the results are encouraging.
"Both trials used electronic cigarettes with low nicotine delivery and it is likely recent products are more effective as previous research suggested higher and faster nicotine delivery will have a greater effect on smoking cessation."
Author of the study, Jamie Hartmann-Boyce said: "None of the studies in this review found that smokers who used electronic cigarettes short-term [2 years or less] had an increased health risk compared to smokers who did not use electronic cigarettes."
The study also found people who used e-cigarettes were more likely to cut down on the number of cigarettes they smoked than if they used a nicotine patch.
It is currently claimed patches are one of the most widely used aids to help people stop smoking, along with gum to help combat nicotine cravings.
More studies are needed to provide further proof of the effects of e-cigarettes and noted some are already underway, said the report.