The federal government may have overpaid for EpiPens by more than a billion dollars over a decade.

That’s according to materials provided to Senate Judiciary Chairman Charles E. Grassley by the office of the inspector general at the Health and Human Services Department about the medical device by Mylan Pharmaceuticals, used to treat severe allergic reactions.

“The fact that the EpiPen overpayment is so much more than anyone discussed publicly should worry every taxpayer,” Grassley said in a statement.

A Wednesday letter to the Iowa Republican from the inspector general’s office said it was possible that the overpayment could reach $1.27 billion, rather than the $465 million that the manufacturer had apparently agreed to pay.

“Mylan and the Obama Administration reportedly were close to settling the overpayment for much less than $1.27 billion,” Grassley said.