Two human trials in the US and the UK including women from both populations showed that women taking newer forms of oral contraceptives, which include drosperinone, a synthetic version of the hormone progesterone, increased their risk of developing a blood clots by two or three times over those taking older birth control pills that rely on a different form of the hormone known as levonorgestrel. These blood clots were not fatal, and the absolute number of cases was small, but the results highlight what doctors have known ever since birth control pills were approved — that the mix of hormones needed to prevent pregnancy also promote clotting factors.
These newer oral contraceptives include Yaz, Yasmin and Ocella, and their makers all include warnings about increased risk of blood clots on the drugs' labels. Bayer, which manufactures Yaz and Yasmin, said in a statement that the study had "significant flaws" and defended the safety of its product. He said, “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.”
Dr. Grace Lau, an obstetrician and gynaecologist at New York University Langone Medical Center, said that while the absolute risk of developing a blood clot on the newer contraceptives was small — 30.8 per 100,000 women years compared with 12.5 events in the control group in the U.S. study — there is still an increased risk. She said, “If a woman has been on Yaz and has had no problems with it, then I don't have a problem continuing to write her prescriptions for it…But for someone who hasn't been on a contraceptive, as a provider I think about what would decrease their risk and I want the best for my patients. So this may not be the first thing I give them, since it may not be the best option they could possibly get.” She however stressed on the absolute risk for individual women that is still low, so each woman should decide for herself which option is right for her. Birth control pills can cause other side effects, from spotting to cramps, and some women may respond better to the newer pills. Taking birth control, however, is not indicated for women who have a history of blood clots or are over 35 and smoke, since smoking increases the risk of clots.
Dr. Steven R. Goldstein, professor of obstetrics and gynaecology at NYU Langone Medical Center in New York City added, “Even if the findings turn out to be real, we're talking about an increase from a very small risk to a very small risk.” “If I have a patient coming in tomorrow starting on birth control, I might not reach for the Yaz or Yasmin product,” said Goldstein. “But I definitely, definitely would not take anybody off Yaz or Yasmin who's been on it six months or a year and is doing well, who has no family history or personal history of venous thromboembolism.”
Bayer is facing class action lawsuits in Canada and the U.S. related to Yasmin, Yaz and generic versions of the drug.