The former chairman of research and development at GlaxoSmithKline, Tadataka Yamada, has been asked by a US Senate committee to explain his role in what it describes as the “intimidation” of John Buse, a professor of medicine at the University of North Carolina.

In 1999 Dr Buse raised questions about the cardiovascular safety of the diabetes drug rosiglitazone, which is marketed as Avandia (BMJ 2007;334:1237 doi: 10.1136/bmj.39244.394456.DB). He was speaking at a symposium organised by the American Diabetes Association.

A report by the Senate Finance Committee staff has shown that a company official emailed Dr Yamada proposing that a “firm letter” be written to Dr Buse containing a warning that “the …