Curious, he started studying vaping at the Onassis center. In 2012, his team found no signs that e-cigarettes disrupted heart function in a short-term study comparing vapers with smokers. As the results came in, he started vaping himself — and was soon off cigarettes for good. The study was presented at a European Society of Cardiology meeting in Munich that August.

Farsalinos’s work got the attention of a young, fast-growing industry eager to show that its products were safer than smoking. In 2013, AEMSA sponsored an e-cigarette nicotine delivery study by Farsalinos and brought him to present his findings to the U.S. Food and Drug Administration, according to a blog post.

Today, Farsalinos touts his findings at scientific conferences around the world, sometimes in countries considering regulations on the devices. This May, he appeared in the Philippines at a harm-reduction conference, admonishing officials to consider vaping’s benefits.

“No one has the right to ignore scientific evidence,” he said, according to a local newspaper.

In June, he spoke in Warsaw at the Global Forum on Nicotine. In Seoul, in August, he gave a speech at the third annual Asia Harm Reduction Forum. In September, he cast doubt on research linking e-cigarettes to heart attacks at a conference in Norway. Later that month, he spoke at a gathering in Washington for the tobacco and nicotine industry.

Farsalinos has many fans online. “Your work is priceless,” said a YouTube commenter about a video of a Farsalinos talk in Oslo. “We will be always grateful for everything you do for the community.”

One of Farsalinos’s favored lines of attack is to argue that scientists who are unfamiliar with vaping tested the products under unrealistic conditions.

In the Portland State study, Farsalinos said that the researchers overheated vaping devices, leading to the discovery of contaminants that wouldn’t otherwise be present at high levels. He likened it to burning toast and declaring that bread has carcinogens in it. Vapers would taste the so-called dry puff and stop. In May 2015, Farsalinos and two colleagues published a rebuttal study in another journal, finding much lower formaldehyde levels.

But some other research teams, including one at Harvard, another at the Lawrence Berkeley National Laboratory and another at the Desert Research Institute in Reno, Nevada, have since reported finding significant formaldehyde levels in some e-cigarette vapors, including at typical voltage settings. Farsalinos has published studies that challenge some of those formaldehyde findings, too.

“I would call it a manufactured debate,” said public health researcher Joseph Allen, senior author of the Harvard study. He likens the tactics to industry sympathizers trying to sow doubt about climate change.