Two contraceptives—Yaz and Yasmin—will be adding information to their labels informing users about the risk of blood clots.

In two long-term studies of 120,000 U.S. and U.K. women, researchers found that Yaz and Yasmin, two of Bayer’s top-sellers, can cause blood clots in some women. These two contraceptives were released in 2000, so little was known about their long-term effects. This risk is comparative to that of other oral contraceptives, but Bayer Health Care, the company that produces the drugs, plans to provide more thorough information to its consumers.

Higher levels of certain hormones in the blood stream from use of birth control pills can cause blood clots. Drospirenone and ethinyl estradiol, the active ingredients in Yaz and Yasmin, don’t necessarily guarantee clotting problems, but they can promote clotting.

When clots do occur, they bring serious medical risks. One such risk, known as deep venous thrombosis (DVT), occurs when blood clots form in larger veins, usually those in the legs. If this clot breaks off into the blood stream (called an embolism), it can become lodged in vital organs and cause serious damage, stroke, or even death.

The risk of clotting is increased when birth control users smoke, have a history of clots, are overweight, have high blood pressure and/or cholesterol, or are over age 35.

Some contraceptives have, however, been shown to regulate periods, prevent ectopic pregnancy and pelvic inflammatory disease (PID), and has a lower incidence of ovarian cancer and cysts. Yaz in particular can be used to treat  premenstrual dysphoric disorder (PMDD). Talking with your doctor can help you find the solution that best fits your needs.

We are convinced of the fact that Yasmin is a good choice for women who wish to have a simple and reliable method of prevention, if the product is used in accordance with (the health guidelines),” Dr. Kemal Malik said in a press release. Malik is the chief medical officer of Bavarian Schering Pharmaceuticals, and worked on the studies.

The risk of blood clots from contraceptives is relatively low—according to Epigee, only about 3 of every 10,000 women using the pill experience clotting. Choosing the right contraceptive can further reduce those risks.

Visit the Yaz/Yasmin site to get the full scoop on these products.