Some birth control pills will come with a new warning about blood clots, the U.S. Food and Drug Administration announced Tuesday.
New studies have shown that pills containing drospirenone, a synthetic version of the hormone progesterone, raise the risk of blood clots, and the FDA mandated that they be labeled accordingly.
Women who use the birth control pill brands Beyaz, Safyral, Yasmin and Yaz are at more risk of developing blood clots than those on pills without drospirenone, the FDA said. Depending on the brand, the risk could be as much as three times higher.
But the agency said the risk is still relatively low, and said women should not stop taking the pill unless so directed by their doctor.
The risk of blood clots is higher when using any birth control pills than not using them, but still remains lower than the risk of developing blood clots in pregnancy and in the postpartum period, the FDA said.
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For every 10,000 women who are not pregnant and do not use the pill, between one and five will develop a blood clot, the FDA said. Between three and nine out of every 10,000 women who use contraceptives will develop a blood clot, and between 40 and 65 women out of 10,000 will develop a blood clot within 12 weeks of giving birth, the organization said.
The greatest risk of developing a blood clot comes in the first year that one starts the pill or after a four-week break. Smoking, obesity and a family history of blood clots raise the risk. Symptoms of a blood clot include red, painful areas on the leg, swelling, shortness of breath and chest pain.
Pills containing drospirenone are marketed as helping to alleviate premenstrual symptoms, cause less weight gain than competitors and reduce acne. However, the manufacturer of Yaz and Yasmin, Bayer, has been subjected to several lawsuits over at least 50 deaths linked to the pills between 2004 and 2008.
Bayer has consistently updated the FDA and other regulatory authorities around the world as new data have become available, Bayer told Bloomberg Businessweek. It also said the company has worked with the agencies to make label updates, as appropriate.
The new labels will take effect immediately.