FRIDAY, March 19 (HealthDay News) -- A new review of studies on the controversial diabetes drug Avandia finds that most of the researchers who reported positive results had financial ties to pharmaceutical companies, but it's not clear if being paid by drug makers directly leads to supportive research.

The review authors found that 94 percent of the researchers who penned positive studies about the drug Avandia (rosiglitazone) had been paid by pharmaceutical companies. The drug, which treats type 2 diabetes, has been linked to heart attacks.

Last month, the U.S. Food and Drug Administration said it was reviewing documents that examine whether Avandia raises the odds for heart attack and heart failure and should be removed from the market. The agency said it plans to hold a public hearing on the evidence in July.

The review authors, who looked at more than 200 studies, wrote that "there was a clear and strong link between the orientation of authors' expressed views on the rosiglitazone controversy and their financial conflicts of interest with pharmaceutical companies."

Forty-five percent of the study authors had financial conflicts of interest, and about a quarter of those didn't disclose it, report the Mayo Clinic researchers.

"These findings, while not necessarily causal, underscore the need for further progress in reporting in order for the scientific record to be trusted," says the review, which is published online March 19 in BMJ.

More information

The U.S. National Library of Medicine has more on Avandia.