10/27/2011 03:03 EDT | Updated 12/27/2011 05:12 EST

US agency says Yaz and other new birth control drugs appear to increase blood clot risk

WASHINGTON - U.S. government regulators say several new birth control drugs, including the Bayer pill Yaz, appear to increase the risk of dangerous blood clots more than older medications.

A new study released by the Food and Drug Administration reviewed the medical history of more than 800,000 American women taking different forms of birth control between 2001 and 2007. On average, woman taking Yaz had significantly higher rates of blood clots than women taking older birth control drugs.

The agency also reports higher complications in women using the Ortho Evra patch from Johnson & Johnson and the Nuvaring vaginal ring from Merck & Co. Inc.

Recent studies have reached differing conclusions on the risks of newer birth control pills. The FDA is holding a meeting in December to discuss the data.