Trying to prevent one unwanted event may cause another. Women who use a newer type of birth control pill containing a hormone called drospirenone, such as Bayer’s Yaz and Yasmin, are more likely to develop blood clots than those who take an older oral contraceptive, according to a pair of studies published in BMJ. However, the overall risk of developing a clot in the lungs or legs was still low.
One study reviewed insurance data for US women aged 15 to 44 who took a contraceptive pill containing either drospirenone or levonorgestrel after January 2002, and compared 186 women who had had a blood clot with 681 who had not. Those taking the newer pill had a 2.3 times greater risk for a blood clot, although the absolute risk was small - 30.8 per 100,000 among those taking drospirenone, compared to 12.5 per 100,000 in women taking levonorgestrel (read the abstract here).
The findings “provide further evidence that levonorgestrel oral contraceptives appear to be a safer choice,” says Susan Jick, a professor of epidemiology in the School of Public Health of Boston University and principal author of the study.
The other study, which reviewed use among similarly aged women in the UK, found a three-fold elevated risk for blood clots among women taking the newer version of the pill. That translated to 23 per 100,000 women in the drospirenone group and 9.1 per 100,000 women in the levonorgestrel group (here is the other abstract).
"Prescribing lower-risk levonorgestrel preparations as the first line choice in women wishing to take an oral contraceptive would seem prudent," says Lianne Parkin, a senior lecturer in the School of Medicine at the University of Otago in Dunedin, New Zealand and senior author of the second paper.
The results are not good news for Bayer, which faces numerous lawsuits over its contraceptives. Nearly 6,900 lawsuits are pending in the US over alleged injuries and deaths relating to Yaz and Yasmin, as well as generics. The lawsuits allege Yaz and Yasmin have risks beyond those of traditional birth control pills and Bayer too aggressively promoted the pills without disclosing higher risks. Bayer was warned by the FDA in 2008 that TV ads were misleading and did not disclose added risks (see here).
In a statement, Bayer questioned the methodology of the studies and contended the results do not offer any new insights. "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."