Widely available next-generation birth control pills may pose an increased risk for blood clots, the Food and Drug Administration announced Oct. 27. FDA's advisory includes birth control pills marketed under the brand names Yaz, Loryna, and others that contain the ingredient drospirenone.

Companies market the drospirenone-containing birth control pills as having the added benefit of alleviating acne.

The FDA reported that women using drospirenone have a 50 percent greater risk of blood clots. At that rate, about six out of 10,000 women will experience blood clots as a side effect of the drug. A study published in October by The British Medical Journal found that drospirenone is more than twice as likely as non-hormonal contraceptives to cause blood clots.

Last May, the FDA first warned the public about the possible greater risks of drospirenone. At the time, the FDA was reviewing study data collected from over 800,000 U.S. women. As of September, there were still conflicting data from six studies related to drospirenone. In October, FDA officials got closer to taking a definitive stance on the risks related to the drug.

Bayer, a manufacturer of drospirenone under the popular brand name Yaz, said in a statement last spring that these side effects are rare, referring to blood clots, heart attack and stroke, but still acknowledging that being overweight and smoking increases those risks. A blood clot can be fatal if it travels through the bloodstream into the lungs, a condition called a pulmonary embolism.

Bayer officials wrote that they believe their existing data about the safety of products containing drospirenone is better than that of the British Medical Journal study.

Bayer's assessment, based on its review to date, is that the manner in which the authors applied the study methodology reported in these two publications and the databases used provide less reliable conclusions than are available from existing scientific evidence around the risk of developing venous thromboembolism (VTE), or blood clots, with combination oral contraceptives (COCs).  Given the already large and robust scientific body of evidence, in Bayer's opinion, these studies do not change the overall assessment about the safety of Bayer's oral contraceptives.

Birth control pills are among the most profitable and popular elective drugs on the market. The Washington Post reported that the Bayer brand Yaz alone brought in $1.6 billion worldwide revenue in 2010.