Teva Pharmaceuticals announced in June 2010 that it has launched a generic version of Bayer’s Yaz birth control pill, which will be marketed as Gianvi. The announcement has sparked a patent infringement lawsuit from Bayer, who claims Teva is breaking an agreement between the two companies.

According to Bayer officials, Teva agreed not to launch generic Yaz until July 2011. Teva officials, however, say that the agreement allowed them to sell the generic birth control pill early under certain conditions.

Yaz is a birth control pill that contains the hormone drospirenone. According to two studies published in British Medical Journal, patients taking birth control pills containing drospirenone are twice as likely to suffer blood clots or other yaz side effects as with another form of birth control.

Bayer currently faces more than 1,100 Yaz lawsuits filed by women who allege that the drug maker failed to warn about the potential side effects of the birth control pill, including stroke, heart attack, pulmonary embolism and deep vein thrombosis. During the first quarter of 2010, Bayer reported a 10% drop in Yaz sales amid growing concerns about the potential side effects of Yaz and Yasmin.