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Study links birth-control pill to increased risk of blood clots

Women who use birth-control pills made with the hormone drospirenone, such as Bayer's Yasmin, are three times more likely to develop blood clots than those who take an older oral contraceptive, a study has found.

The overall risk of developing a clot in the lungs or legs was still low for women using drospirenone, according to the study published Friday in the British Medical Journal. The research examined British database reports on almost 300 women.

The results support earlier findings from European studies that drospirenone appears to have a higher risk of clots compared with the older levonorgestrel, according to the U.S. and New Zealand researchers. They also contradict two industry-funded studies that found the hormones had a similar clot risk, said the researchers, led by Susan Jick, a professor of epidemiology at the Boston University School of Medicine.

"Prescribing lower-risk levonorgestrel preparations as the first-line choice in women wishing to take an oral contraceptive would seem prudent," said the researchers in the study. "Perhaps now is the time for a systematic review on this topic."

A separate study, which was also led by Jick and published in the journal Friday, found a doubling of the risk of clots in women who took drospirenone compared with levonorgestrel. That research was based on U.S. insurance claims information on almost 900 women. Women taking any kind of contraceptive pill have a fivefold higher risk of blood clots compared with those who don't, previous research has found.

Bayer's Beyaz, Yaz and Angeliq pills also contain drospirenone, which is similar to the natural female hormone progesterone. Levonorgestrel, which also resembles progesterone, is used in contraceptives made by companies including Bayer, Teva Pharmaceutical Industries and Pfizer.

About 6,850 lawsuits were pending in the United States as of Feb. 1 over alleged injuries and deaths as a result of the use of Yasmin, Yaz, or Teva's generic versions of the drugs, according to Bayer's annual report. Bayer also faces 13 class action suits in Canada. Additional lawsuits are anticipated, Bayer said in the report.

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