In a new drug safety communication posted today on the U.S. Food and Drug Administration’s website, the agency announced that preliminary results of a study involving 800,000 women suggest a 1.5-fold increase in the risk of blood clots for those women using drospirenone-containing birth-control pills, compared to those taking other forms of hormonal contraceptives. Popular and controversial brands such as Yaz and Yasmin, both marketed by Bayer AG, are prime examples of the type of drospirenone-containing pills currently under scrutiny by federal regulators.

It is important to note that the FDA has yet to reach a final conclusion that drospirenone-containing pills raise the risk for blood clots beyond that of other pills. However, the regulatory agency still remains greatly concerned over the potentially fatal side effects linked to use of birth control pills that contain drospirenone. At the moment, conflicting information from a number of published studies regarding the blood-clot risk associated with drospirenone, has prompted the FDA to convene an outside panel of medical experts to further discuss the issue in December.

According to Bayer, available scientific evidence shows that the risk for developing blood clots as a result of taking birth-control pills containing drospirenone is “comparable” to that of other pills studied, but the company is still working with the FDA on the matter.