Watson Pharmaceuticals Inc. said Friday it is challenging Bayer's patent on the birth control pill Beyaz.
Watson said Bayer responded by filed a lawsuit accusing Watson of patent infringement. The Food and Drug Administration will not approve Watson's generic until the lawsuit is resolved or 30 months have passed, whichever happens first.
Beyaz also is used to treat premenstrual dysphoric disorder. It is a reformulation of earlier, popular birth control pills from Bayer, including Yaz, which the U.S. Food and Drug Administration has found may be associated with a higher risk of blood clots. By December, the FDA had not set a timetable for any changes in Yaz's labeling.
Watson said U.S. sales of the drug totaled $97 million in 2011.
Shares of Watson Pharmaceuticals fell 26 cents to close Friday at $57.99 but regained 15 cents after hours.