If you need a drug for type 2 diabetes, we’ve long advised that a time-tested older medication called metformin is your safest bet and documents from the Food and Drug Administration released over the weekend underscore why. The controversial diabetes drug Avandia already carries a warning that it can cause heart failure, but some FDA officials think the medication also causes heart attacks and should be pulled from the market. According to internal reports* (released by the Senate Finance Committee), FDA officials speculate that if patients on Avandia were switched to a different drug called Actos, 500 heart attacks and 300 cases of heart failure could be prevented every month.

The FDA documents were discovered in a two-year investigation into Avandia by the Senate Committee on Finance, which charged that the manufacturer, GlaxoSmithKline, knew of the heart risks associated with the drug for years before the danger was made known to the public. Avandia now carries a black box warning—the FDA’s strongest—that the drug can cause or worsen heart failure.

The report also had grave concerns about the FDA’s handling of a currently active study called the TIDE trial that is comparing the heart risks of Avandia to Actos or placebo. In the internal FDA reports, FDA officials called the trial unethical and unsafe for patients, given the known heart risks of Avandia. If you are involved in this trial, ask your doctor whether Avandia or Actos is appropriate for you. Actos also carries a warning that it can cause heart failure).