At a meeting of tobacco researchers this week in Philadelphia, this question was posed over and over: Can electronic cigarettes help tobacco smokers quit?

"FDA can't make regulatory policy on the basis of anecdotal evidence, but we're maintaining an open mind, and we hope the public will have an open mind too," was the answer from Mitch Zeller, director of the Center for Tobacco Products at the U.S. Food and Drug Administration.

Anecdotes are many from smokers who say they've tried everything -- hypnosis, will power, nicotine patches, therapy -- but were unable to quit tobacco until electronic cigarettes came along.

Several surveys suggest that vaping has helped some smokers kick the habit, but, so far, only two clinical trials have focused on the effectiveness of e-cigarettes as a cessation tool. A review of those studies found that more smokers were able to cut back when using an electronic cigarette with nicotine rather than a vaping tool without nicotine.

Sometimes called "hookah pens" or "vape pipes," electronic cigarettes use a battery to heat liquid nicotine. Users inhale the resulting vapor to get a buzz from nicotine, but e-cigs don't produce smoke.

At the meeting of the Society for Research on Nicotine and Tobacco, many were speculating about if, when and how the federal government might regulate electronic cigarettes. FDA officials say they are working to make an announcement by June on the plan to extend the agency's oversight authority. That process is called "deeming."

"We proposed a minimum age of sales for products like hookah, e-cigarettes and cigars. We proposed a ban on vending machines, and we proposed a series of health warnings," Zeller said.

But Philadelphia and New Jersey already have forbidden vapers from puffing on e-cigs in indoor public spaces. What if the federal rules are different?

According to several experts, it depends. Federal labeling rules – or a law to require manufacturers to make childproof packaging -- would likely trump local laws. But Philadelphia and other places would be free to write rules about where e-cigarettes can be used, or impose stricter taxes.

That push is dead in Philadelphia in the estimation of industry advocate Gregory Conley with the American Vaping Association. E-cigarettes have lower health risks, Conley said, and should not be regulated in the same way as conventional cigarettes.

Thomas Eissenberg, a psychologist at Virginia Commonwealth University and co-director of the Center for the Study of Tobacco Products, said the federal government's regulations should be based on scientifically collected data.

"Not based on what we think is the right thing to do, because we've often thought wrong," he said.

This week, he and his colleagues debated what kind of research the FDA needs.

Eissenberg's team talked about perhaps regulating "nicotine flux" – the amount of the drug that comes out of the mouth-end of a vaping pen.

He says there must be enough nicotine produced so the experience is satisfying to smokers -- and helps them quit tobacco cigarettes.

"There's a sweet spot," he said. "We don't want a level that's so high that adolescents or non-smokers will pick up electronic cigarettes and start using them."