April 22nd, 2011
02:12 PM ET
Women who are using a newer version of birth control that contains the hormone drospirenone have a higher risk of serious blood clot, according to two studies published in the online version of the British Medical Journal.
Drospirenone is found in birth control pills such as Ocella, Yasmin and Yaz.
The studies found that drospirenone has two to three times more risk of blood clots compared with birth control pills containing an older form of a progestin hormone called levonorgestrel. Dr Susan Jick, lead authors said that these findings “provide further evidence that levonorgestrel pills appear to be a safer choice” pertaining to blood clots.
Drug makers dispute the findings, saying the studies are flawed.
The research, led in the U.S. by Jick from the Boston University School of Medicine, used information from United States medical claims data and a United Kingdom research database.
In the U.S., the study reported that in one year, there are 30.8 blood clots per 100,000 women using the birth control containing drospirenone. That rate was lower with 12.5 blood clots for the older birth control pills using levonorgestrel.
"What’s important is that the risk is quite low," Jick said. "30 in 100,000 women is not very many blood clots. It is not that common, but it does happen more in drospirenone than levonorgestrel."
In the U.K., the yearly rates for blood clots were 23 clots per 100,000 women using the drospirenone pill and 9.1 for levonorgestrel.
"There is a risk no matter which oral contraceptive you choose to take," Jick said. "The risk appears higher in drospirenone, than levonorgesterel. Users should just be aware when they’re making a choice that there is a higher risk than the other."
Bayer, the maker of Yaz, challenged the study's methodology and the databases used, saying that they “provide less reliable conclusions than are available from existing scientific evidence.”
“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.” The company said that the blood clot risk of using contraceptives that contain drospirenone is the same as those in the older birth control pills.
According to Bloomberg News, 6,850 lawsuits were pending in the U.S. as of February 1 over alleged injuries and deaths as a result of the use of Yasmin, Yaz, or generic versions of the drugs.
Physicians cautioned against making knee-jerk reactions to the findings:
- Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center in New York told WebMD, “These are strong studies, but they will not change the way I practice except that this information will be part of my conversation with patients,”
- André Lalonde, vice-president of the Society of Obstetricians and Gynecologists of Canada, cautioned against jumping to conclusions. In the Globe and Mail, he said: “Each time a new product comes out, we see this – it’s the new pill effect. Risks and complications are always greatest in new patients, much higher than those who have used the same product for a long time."
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