When combined with one-on-one behavior therapy, e-cigarettes are more effective in helping people quit smoking than traditional nicotine-replacement products such as patches and gum, according to a new randomized study of British adults published Wednesday in the New England Journal of Medicine.

Axar.az reports that "E-cigarettes were almost twice as effective as the 'gold standard' combination of nicotine replacement products," lead researcher Peter Hajek from Queen Mary University of London said in a statement.

"Health professionals have been reluctant to recommend their [e-cigarette] use because of the lack of clear evidence from randomized controlled trials. This is now likely to change."

But US researchers urge caution, saying the study's results are not conclusive or easy to generalize. They also point to the unknown long-term health effects of e-cigarette vapor on the body, as well as dangers of possibly encouraging e-cigarette use among teens.

The study's results have already been widely embraced by experts in the UK, many of whom agree that e-cigarettes should be included in adult anti-smoking efforts.

"This study should reassure policymakers and health professionals -- mainly beyond the UK -- who have until now been hesitant to recommend e-cigarettes for smoking cessation on the basis that there was a lack of high-quality trial evidence," said Jamie Brown, who serves as deputy director of the Tobacco and Alcohol Research Group at University College London.

"We need to help as many people as possible to give themselves the best chance of success by using aids like e-cigarettes each time they try to stop smoking," Paul Aveyard, a professor of behavioral medicine at the University of Oxford, said in a response to the study.

But American researchers and policymakers are not convinced.

"The US Food and Drug Administration has not found any e-cigarette to be safe and effective in helping smokers quit," said Jennifer Hobbs Folkenroth, who is the American Lung Association's senior director of tobacco. "We only support methods that are FDA approved and regulated."

Smoking cessation researcher Belinda Borrelli, who wrote an editorial published in conjunction with the study, points to concerns about the possible long-term health effects of e-cigarette use on adults and the growing numbers of children in the United States who are becoming addicted to e-cigarettes.

FDA Commissioner Dr. Scott Gottlieb recently announced a crackdown on what he called an "epidemic" of e-cigarette use among teenagers.

"E-cigarettes have volatile organic compounds, cancer-causing chemicals, and flavorings that have been linked to lung disease," said Borelli, who directs the Center for Behavioral Science Research at Boston University. "Let's not say e-cigarettes are a magic pill to help people quit smoking without having all of the information."