In a win for three generic drug companies, the U.S. Court of Appeals for the Federal Circuit has invalidated key claims in Bayer AG’s patent on the brand-name oral contraceptive Yaz.

In a 14-page decision issued on Tuesday, the Federal Circuit ruled that the hormone formulation in Yaz was obvious to scientists at the time. Generic drug companies Actavis Inc., Sandoz Inc. and Lupin Ltd. had challenged Bayer’s patent through Hatch-Waxman Act litigation.