A leading member of the U.S. Senate says that a diabetes expert who was asked to review a controversial study on the risk of Avandia side effects leaked its findings to the drug’s manufacturer, GlaxoSmithKline.

The study by diabetes expert Dr. Steven Nissen was published in May 2007 in the New England Journal of Medicine. Dr. Nissen’s study concluded that patients using Avandia to treat their diabetes symptoms were 64% more likely to die of heart problems and 43% more likely to suffer a heart attack than other patients.

One of the doctors who reviewed the study before it was published was Steven Haffner, himself a diabetes specialist. But after reviewing the study, Dr. Haffner faxed a copy of it to GSK, which is a violation of both NEJM rules and the ethical standards set by doctors. The journal suspended another doctor from reviewing or commenting upon its articles for five years after similarly leaking a study of the health risks of drug-coated stents last year.

Dr. Haffner has received $75,000 in consulting and speaking fees from GSK since 1999. He also took part in clinical trials conducted by GSK for Avandia and published an article criticizing Dr. Nissen’s findings about the risk of Avandia side effects.

As a result of Dr. Nissen’s study, the Food and Drug Administration decided to add a black box warning to Avandia’s label to warn patients about the risk of Avandia side effects they faced by taking the drug.