Bates, who said he organized the petition against Peyton’s study in his spare time, disputed the notion that the pushback is highly coordinated. Anti-vaping forces are far better-funded, he said, citing initiatives financed by Michael Bloomberg, the founder and majority owner of Bloomberg LP, which owns this news service. Bloomberg has campaigned and given money in support of a ban on flavored e-cigarettes and tobacco.

“It is a completely asymmetrical conflict,” Bates said.

Smoking remains a leading cause of preventable death and disease worldwide, and its effects kill about 480,000 Americans a year, the CDC says. Cigarette use is high in Europe and especially so in Greece, making finding ways for people to quit a matter of compelling interest.

In a survey of current and former smokers near Athens, Farsalinos found that many who quit cigarettes had used e-cigarettes, “suggesting a positive public health impact in a country with the highest prevalence of smoking in the European Union,” according to a paper he and colleagues published this year in the journal Internal and Emergency Medicine.

Farsalinos said he receives no money from e-cigarette companies and that his salary is paid by a government scholarship.

But some research he conducted several years ago was sponsored by industry associations and e-cigarette companies, according to disclosures in medical journals. They include the American E-Liquid Manufacturing Standards Association (AEMSA); the Tennessee Smoke Free Association; Nobacco, a Greek e-cigarette company; and FlavourArt, a maker of so-called e-liquids.

Farsalinos’s two studies for the American E-Liquid Manufacturing Standards Association were undertaken independently to answer questions from U.S. regulators, and the trade group “had no input” in how they were done, AEMSA President Scott Eley said in an email.

Nobacco sponsored a study at the Onassis Cardiac Surgery Center, looking at the effects of e-cigarettes on the elasticity of blood vessels, according to its website. Nobacco funded the study in 2013 and says it has not sponsored any Farsalinos studies since then.

The Tennessee Smoke Free Association said its study with Farsalinos focused on how flavors in e-cigarettes help people switch from regular cigarettes, and results were submitted to regulators. FlavourArt funded a 2013 Farsalinos study showing that e-cigarette vapor didn't harm cells, but hasn’t worked with him since then, a company spokesperson said.

Farsalinos knew nothing about e-cigarettes in 2011, when he was sent a picture of two friends vaping. He thought it was a waste of time. At the time, he smoked a pack and a half of cigarettes a day, and he had tried everything to quit, from nicotine gum to prescription treatments, without success.