"In contrast to the assumption that e-cigarettes would function as a better form of NRT [Nicotine Replacement Therapy], population-based studies that reflect real-world e-cigarette use found that e-cigarette use is not associated with successful quitting; all4,79,80,82 had point estimates of the odds of quitting of <1.0. The 1 clinical trial examining the effectiveness of e-cigarettes (both with and without nicotine) compared with the medicinal nicotine patch found that e-cigarettes are no better than the nicotine patch and that all treatments produced very modest quit rates without counseling.86 Taken together, these studies suggest that e-cigarettes are not associated with successful quitting in general population-based samples of smokers."

Source

Rachel Grana, Neal Benowitz and Stanton A. Glantz, "Contemporary Reviews in Cardiovascular Medicine: E-Cigarettes: A Scientific Review," Circulation (Dallas, TX: American Heart Association, May 13, 2014). 2014;129:1972-1986. doi: 10.1161/CIRCULATIONAHA.114.007667, pp. 1980-1981.
http://circ.ahajournals.org/c…
http://circ.ahajournals.org/c…