The controversy surrounding GlaxoSmithKline's (GSK) diabetes drug Avandia has been exacerbated by claims from a medical expert that he was threatened with a $4bn lawsuit to try to silence his criticisms of the company's controversial diabetes drug.
John Buse testified at a Senate hearing that he felt so intimidated by company employees that he sent a desperate letter to a board member asking him to "call off the dogs".
Dr. John Buse says in 1999 after drawing attention to a trend in heart problems among patients using Avandia, he was contacted by GSK.
He says threats and a smear campaign against him began after he publicly warned that there may be heart risks associated with Avandia, then a brand new drug.
Dr. Buse who is a respected diabetes researcher is about to take over as president of the American Diabetes Association.
He believed salesmen at GSK were exaggerating the benefits of Avandia and that there should have been a proper study into the heart risks of the drug.
At the time GSK dismissed him as a "liar" and impugned his integrity and matters came to a head when he was threatened with the lawsuit.
Eight years down the line, with a million Americans now taking Avandia on a regular basis, a study last month concluded that the pill significantly raises the risk of heart attacks and fatal heart problems.
Buse says though he eventually signed a clarifying statement with the company that was used to ease concerns from investors, a year later he sent a letter to the Food and Drug Administration raising the same concerns.