A large study in England has found smokers trying to quit were substantially more likely to succeed if they used electronic cigarettes than over-the-counter therapies, such as nicotine patches or gum. These results offered encouraging – but not definitive evidence – in the contentious debate about the risks and benefits of these increasingly popular smoking devices.

Researchers interviewed almost 6,000 smokers who had tried to quit on their own without counseling from a health professional. About a fifth of those who said they were using e-cigarettes had stopped smoking at the time of the survey, compared with about a tenth of people who had used patches and gum.

“This will not settle the e-cigarette issue by any means,” said Thomas J. Glynn, a researcher at the American Cancer Society, who was not part of the study, “but it is further evidence that, in a real-world context, e-cigarettes can be a useful, although not revolutionary, tool in helping some smokers to stop.”

Use of e-cigarettes has risen rapidly across Europe and the United States, and regulators are scrambling to figure out how to respond in the absence of hard evidence about their effects. The debate is particularly fierce in the United States, where some experts say the devices could lure children to start smoking.

About 42 million Americans smoke, and about 480,000 people die every year from smoking-related illnesses – this country’s leading cause of preventable death. The central question is whether e-cigarettes will cause the ranks of smokers to shrink or swell.

The English study was not a clinical trial, the gold standard of scientific research.

Robert West, director of tobacco studies at University College London and senior author of the study, which is to be published in the journal Addiction, said clinical trials could not answer the question most people have about whether e-cigarettes help smokers quit because the devices are changing so fast that they become obsolete before an experiment ends.