April 21, 2011 -- Women who take birth control pills with the newer hormone drospirenone have a higher risk for developing potentially serious blood clots than women who take oral contraceptives containing the older hormone levonorgestrel, two new studies show.
The studies are published in BMJ Online First.
Women in the studies who took the drospirenone-containing pills, such as Gianvi, Ocella, Yasmin, Yaz, and Zarah, had a twofold to threefold increased risk of nonfatal blood clots compared to women who took oral contraceptives that contained levonorgestrel, such as Jolessa, LoSeasonique, Quasense, Seasonale, and Seasonique.
But the maker of Yasmin and Yaz says the study was flawed.
Study researchers say the risk to individual users is small. By their estimates roughly three women out of 10,000 who take the drospirenone-containing pill for a year could be expected to develop a clot, compared to about 1.2 women in 10,000 who take levonorgestrel.
“The [clot] risk in pregnancy is much higher than for any oral contraceptive,” study researcher Susan S. Jick, PhD, of Boston University School of Medicine, tells WebMD. “Nevertheless, women taking these pills or considering taking them should be aware that there is very likely an increased risk associated with their use.”
At least four other studies have linked use of drospirenone-containing birth control pills to an increased risk for pulmonary embolisms and deep vein thrombosis. But all four studies included women with known risk factors for the conditions.
These women were excluded from the newly published studies, in which investigators examined medical claims data among oral contraceptive users in the U.S. and the U.K.
In the U.S. study, users of the drospirenone-containing pills were twice as likely to experience nonfatal blood clots as users of the older-generation levonorgestrel-containing pills.
In the U.K. study, use of the drospirenone pill was associated with a threefold increase in risk.
The researchers call for a systematic review of all the studies examining blood clot risk associated with the use of birth control pills containing drospirenone.
“In the meantime,” they write, “as no clear evidence exists to show that the use of the drospirenone pill confers benefits above those of other oral contraceptives in preventing pregnancy, treating acne, alleviating premenstrual syndrome, or avoiding weight gain, prescribing lower risk levonorgestrel preparations as the first line choice in women wishing to take an oral contraceptive would seem prudent.”
In a written statement, officials from Bayer Healthcare, maker of the birth control pills Yasmin and Yaz, contend that the methodology used in the two studies was flawed.
“Bayer re-affirms that the overall body of available scientific evidence continues to provide support that the risk of developing venous thromboembolism, or blood clots, in women using drospirenone-containing combination oral contraceptives is comparable to other combination birth control pills studied,” the statement reads.
The company notes that oral contraceptives like Yaz and Yasmin are among the most widely studied and widely used prescription drugs on the planet.
Ob-gyn Jill Rabin, MD, did not take part in the studies, but called them very well designed and well executed.
Rabin is chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center in New Hyde Park, N.Y.
“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,” she tells WebMD. “These are very popular contraceptives, but there are a lot of contraceptives out there. It is important that patients understand the potential risks and benefits.”