However, e-cigarettes were more effective in reducing cigarette use among smokers who didn't quit.
E-cigarettes are battery-powered devices that deliver nicotine, flavorings and other chemicals. They turn these substances into vapor that is inhaled by the user.
The new study included 657 smokers who used either e-cigarettes, fake e-cigarettes (they didn't contain any nicotine) or nicotine patches for 13 weeks. At the end of the six-month study, about 6 percent of the participants had successfully quit.
Rates of those who successfully quit were 7.3 percent in the e-cigarette group, 5.8 percent in the nicotine patch group and 4.1 percent in the fake e-cigarette group.
These differences were not statistically significant, according to study leader Chris Bullen, director of the National Institute for Health Innovation at the University of Auckland in New Zealand, and colleagues.
The findings suggest that e-cigarettes are comparable to nicotine patches in helping people quit smoking for at least six months.
Among participants who did not quit smoking, 57 percent of those in the e-cigarette group had reduced their daily consumption of cigarettes by at least half after six months, compared with 41 percent of those in the nicotine patch group, according to the study published online Sept. 7 in The Lancet and presented at the annual meeting of the European Respiratory Society, held in Barcelona, Spain.
About 90 percent of those who used e-cigarettes -- including the fake version -- would recommend them to family and friends, compared with 56 percent of those in the nicotine patch group, the researchers said. They also concluded that e-cigarettes are comparable to nicotine patches in terms of safety.
"While our results don't show any clear-cut differences between e-cigarettes and patches in terms of quit success after six months, it certainly seems that e-cigarettes were more effective in helping smokers who didn't quit to cut down," Bullen said in a journal news release.
"It's also interesting that the people who took part in our study seemed to be much more enthusiastic about e-cigarettes than patches, as evidenced by the far greater proportion of people in both of the e-cigarette groups who said they'd recommend them to family or friends, compared to patches," he added.
Bullen continued: "There is still so much that is unknown about the effectiveness and long-term effects of e-cigarettes. Given the increasing popularity of these devices in many countries, and the accompanying regulatory uncertainty and inconsistency, larger, longer-term trials are urgently needed to establish whether these devices might be able to fulfill their potential as effective and popular smoking cessation aids."
This is a "pioneering study" that suggests e-cigarettes have the potential to increase the number of smokers who quit and to reduce costs to quitters and health care systems, Peter Hajek, a professor and director of the tobacco dependence research unit in the Wolfson Institute of Preventive Medicine at Queen Mary University of London, wrote in an accompanying journal commentary.
The American Cancer Society offers a guide to quitting smoking.