“Health professionals have been reluctant to recommend their use because of the lack of clear evidence from randomized controlled trials. This is now likely to change,” said Peter Hajek, the lead author of the study and a professor of clinical psychology at Queen Mary University of London, which coordinated the clinical trials through public “stop-smoking clinics.”

The New England Journal devoted much of its current issue to e-cigarettes, publishing two editorials and a letter, and the collection embodies the tangled public health debate over the devices. One editorial — written by Belinda Borrelli, a behavioral health expert and Dr. George T. O’Connor, a pulmonologist — pumped the brakes on inclinations to embrace e-cigarettes.

They noted that 80 percent of the study participants who had quit by using e-cigarettes were still vaping at one year, while only nine percent of the nicotine replacement therapy group was still using nicotine products. That raised concerns, they wrote, about sustained nicotine addiction and the unknown health consequences of long-term e-cigarette use.

The editorial recommended that e-cigarettes be taken up when other cessation approaches, including behavioral counseling, have failed; that patients use the lowest dose of nicotine possible; that health care providers establish a clear timeline for e-cigarette use.

Another editorial implored the Food and Drug Administration to ban all nicotine flavors for vaping devices because of their appeal to adolescents.

The clinical trial took place from May 2015 to February 2018. Because the smokers were recruited at the clinics, they were already predisposed to quitting, a feather on the scale that could slightly have affected results. The participants were typically middle-aged, smoked between half a pack and a pack a day and had already tried quitting.

The e-cigarette subjects were given a starter kit with a refillable device and one bottle of tobacco-flavored nicotine e-liquid, with 18 milligrams per milliliter — the most common product in England.