One month after a pair of studies found that women taking birth control pills containing a hormone called drospirenone are more likely to develop blood clots than those who take an older oral contraceptive, the FDA has decided to review the evidence. But since other studies have not reported the same risk, the agency is not taking any additional action at this time. The most widely known oral contraceptives containing this hormone are the Yaz and Yasmin pills sold by Bayer.

You may recall that 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 newers 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.

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 (you can read both abstracts here and here).

The ongoing scrutiny is not good news for Bayer. 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) and recently was chastised in the UK for running a Yasmin ad that boasted the pill could prove beneficial on the same problems it may cause (read this).

“The FDA is aware of two newly published studies that evaluated the risk of venous thromboembolism (VTE) in women who use birth control pills that contain drospirenone…These two new studies reported that there is a greater risk of VTE associated with birth control pills that contain drospirenone. This risk is reported to be up to 2 to 3 times greater than the risk of VTE associated with using levonorgestrel-containing pills. Other studies have not reported an increase in risk. FDA is currently evaluating the conflicting results from these studies and will look at all currently available information to fully assess the risks and benefits of drospirenone-containing birth control pills,” the agency states.

At the time the studies were published, Bayer issued a statement questioning the methodology and contend that the results did not offer any information (back story). The drugmaker, however, has been touchy about criticism of its pill. Also last month, a Swiss appeals court ruled that a series of television shows about the possible side effects attributed to its pills were not inaccurate and, therefore, legal intervention was not warranted. The programs focused noted reports of nearly 200 deaths among women who used the pills. Bayer charged the programs were manipulative and mistakenly gave the impression the pills are dangerous (see this).

UPDATE: A Bayer spokeswoman sends us a statement containing this message: “Bayer’s analysis of the overall body of available scientific evidence continues to support its current assessment about the safety of its oral contraceptives, including that the risk of developing VTE in women using drospirenone-containing COCs is comparable to other birth control pills studied. This assessment is supported by consistent clinical findings over a 15-year period and up to 10 years of post-marketing study results which support that the risk of VTE is comparable with any COC studied, regardless of the progestin. In accordance with Bayer HealthCare’s pharmacovigilance program, the company conducts ongoing monitoring of post-marketing surveillance data for all of its products. Bayer will continue to work closely with the FDA on this matter.”