It isn't every clinical scientist who in the space of a month sends a major drug company's stock plummeting, is invited to testify at Congress and is crowned one of the world's 100 most influential people by Time magazine. But then, they aren't Steven Nissen, the cardiologist who last week fingered the diabetes drug Avandia as carrying a possible risk of heart attacks (see Weighing up the evidence).

Credit: A. SANCETTA/AP

This is not the first or most famous case for Nissen, 58, who is based at the Cleveland Clinic in Ohio. In 2001, while serving on a committee of external advisers to the US Food and Drug Administration (FDA), he raised concerns about the safety of a painkiller called Vioxx. Before then, he had made his name pioneering an ultrasound technique that allowed doctors to see fatty plaques of atherosclerosis (see Nature Med. 11, 700; 2005).

Since Vioxx, Nissen says that he has become more concerned about the scientific rigour of drug regulation, prompting him to dig into clinical-trial data that suggest hidden drug risks. “I don't go looking for these things, but they sure seem to find me,” he says. Between running trials for several drug companies, he has flagged cardiovascular risks in drugs for everything from attention deficit hyperactivity disorder to heart failure itself, often costing companies millions in the process.

He will persevere for what he believes is right.

His fans praise him for refusing to pull his punches. “He will persevere for what he believes is right, regardless of the toes on which he may tread,” says Peter Libby, chief of cardiology at Brigham and Women's Hospital in Boston, Massachusetts, who has worked with Nissen for twelve years.

But his methods have earned him enemies, too, many of whom contend that he is more interested in felling the next Goliath than in seeking scientific truth. “The caped crusader Nissen is at it again,” groused a critic on the Wall Street Journal's health blog on 21 May. Bob Temple, director of medical policy at the FDA's drug review centre, has also taken a shot at Nissen. Temple told RPM Report that he was “sort of stunned” by Nissen's suggestions to Congress that senior FDA officials had overruled their underlings' safety concerns. “I can tell you, he didn't see that,” Temple said.

Nissen certainly isn't always right. Speaking to journalists last October, he put Pfizer's cholesterol drug torcetrapib, for which he was overseeing a clinical trial, at the top of a list of hot stories that reporters should watch in 2007. Weeks later, Pfizer pulled the plug on the drug when it was found to raise death rates in late-stage trials (see Nature 444, 794–795; doi:10.1038/444794a 2006).

“After the torcetrapib business, I thought I would lay low for a while,” Nissen said last week. “Then I stumble across this [Avandia] problem and here we are again.”