NJOY’s investors include Sean Parker, the Napster co-founder and former president of Facebook, and Bruno Mars, the pop star.

But NJOY’s share of the convenience store market has gone into free fall, dropping more than half in the last year to less than 10 percent, according to Wells Fargo Securities. Consumer surveys suggest that most people who use e-cigarettes — including those who have smoked — tend to prefer flavors other than tobacco. In the next few weeks, NJOY plans to expand into flavors like “Butter Crumble” and “Black and Blue Berry.” Mr. Weiss said in an interview that the company had little choice after focus groups showed that flavors were “critical.”

“Flavor is essential to vapers’ satisfaction,” Mr. Weiss said. He added that research funded by his company showed that flavors “provide no additional appeal to youth.”

Image Flavors like “Banana Split,” are more popular than traditional tobacco tastes. Credit... Nick Oxford for The New York Times

The e-cigarette market is rapidly shifting, and flavors are central to that. Viking Vapor, one of hundreds of websites selling e-cigarettes, offers 13 pages of alphabetized flavors, from Apple to Watermelon Menthol. But the market for disposable e-cigarettes, commonly found in convenience stores and sold by the likes of NJOY, Vuse and Blu eCigs, appears to be slowing — consumers seemed to be switching to more powerful devices, analysts said. According to Wells Fargo, consumer sales of e-cigarettes at convenience stores fell 17 percent in the month that ended June 7, after falling 10 percent the month earlier — the first time since e-cigarettes came onto the market that consumers spent less at convenience stores. Wells Fargo hypothesized that sales were gravitating to the Internet and “vape” stores, where figures are harder to measure.

Some in public health circles see the debate over flavorings as a sideshow. The central question, they say, is whether e-cigarettes are effective tools to get people to stop smoking tobacco. Others say the issue of flavors crystallizes the debate about the risks and benefits of these products, which many consider far safer than conventional cigarettes. At the same time, there is widespread concern that use of e-cigarettes will renormalize the act of smoking and invite in a new generation of participants, particularly through the lure of flavors.

”It defies logic to think that such flavors would not make e-cigarette use more appealing and even normal for children,” said James Pankow, a chemistry professor at Portland State University in Oregon, who has studied cancer risk from cigarettes.