Birth control pills that contain the hormone drospirenone must now carry a warning that they may increase the risk for potentially fatal blood clots, according to the FDA.

Drospirenone is a synthetic version of the female sex hormone progesterone. Birth control pills containing this hormone include Bayer Healthcare Pharmaceutical's Beyaz, Safyral, Yasmin, and Yaz brands, as well as several other brands (Gianvi, Loryna, Ocella, Syeda, and Zarah).

The new action is the result of an extensive review of the literature. The FDA stated that manufacturers must add information to product labels about studies linking these birth control pills to blood clot risks. The revised drug labels will state that some studies have found as high as a threefold increase in the risk of blood clots among women taking these contraceptives, compared with those who took other progestin-containing pills. Other studies found no additional risk of blood clots

Women should talk to their doctors about their risk for blood clots before choosing a birth control method, the FDA states.