In a move that might harm the popularity of new birth control pills, the US Food and Drug Administration has said that it was adding more information to the labels like Bayer AG’s Yaz and Yasmin, to show that these pills may increase the chances of blood clots.

FDA released a report on Tuesday to update the information about the risk of blood clots in women who take new type of birth control pills that contain drospirenone.

Drospirenone is a synthetic version of the female hormone, progesterone, also referred to as a progestin.

Most birth control pills contain two types of hormone-estrogen and progestin. Birth control pills act by preventing the release of eggs from the ovaries and changing the cervical mucus and the lining of uterus to prevent pregnancy.

‘FDA has concluded that drospirenone-containing birth control pills maybe associated with higher risk of blood clots than other progestin containing pills. FDA is adding information about the studies to the labels of drospirenone-containing birth control pills, FDA said in a statement released on Tuesday.

The statement came after the agency concluded its review of recent observational studies regarding the risks of blood clots in women who take drospirenone-containing pills. Some reports suggest that these pills come with three-fold increase in the risk of blood clot. In general, all birth control pills increase the chances of a woman developing a blood clot that could, in some cases, lead to death.

Blood clots can be fatal if the clot breaks loose and travels to the lungs or heart. Centers for Disease Control and Prevention (CDC) estimates that about 300 000 to 600 000 Americans have complications related to blood clots like Deep Vein Thrombosis or Pulmonary Embolism.

The FDA added that risk of blood clot from pregnancy is still higher than the risk from birth control pills.

Popular brands like Bayer AG’s Yaz and Yasmin along with Sandoz’s Loryna are in the list of pills that contain drospirenone.  Some reports suggest that Bayer earned $374 million in Yaz sales in the year 2010.

The review of pills containing drospirenone came after many groups like ‘the Project of Government Oversight’ reported that FDA’s advisers had ties with makers of the pills containing drospirenone.

FDA recommends that women, who are over age 35 and smoke, should not take any type of combination birth pill, due to increased risk of serious cardiovascular events.

In addition to prevention of pregnancy, some birth control pills containing drospirenone are also approved to treat symptoms of premenstrual dysphoric disorder (PMDD), to treat moderate acne, and to raise folate levels, in women who choose to use an oral contraceptive for birth control.