Birth Control Pills: Some Brands Carry Higher Risk of Blood Clots

By LARA SALAHI (@LaraSalahiABC)
April 22, 2011

Two new studies add to the growing evidence that birth control pills containing a newer type of progestin may put some women at higher risk for blood clots.

Both studies, published today in the British Medical Journal, found that women who took pills containing drospirenone -- which includes the brands Yasmin, Yaz and Ocella -- more than doubled their risk of nonfatal blood clots when compared with those who took pills containing levonorgestrel, an older form of progestin, included in the brands Levlite or Levlen.

But the overall risk for blood clots with any birth control pill -- whether it contains drospirenone or levonorgestrel -- remains low, said Dr. Lauren Streicher, an assistant professor of obstetrics and gynecology at the Feinberg School of Medicine at Northwestern University.

"While there may be an increase in blood clots, it's important to keep in mind that the likelihood of developing a blood clot is so low in a low-risk population that a two- to three-fold increase may not translate to large absolute numbers," said Streicher.

Women who are pregnant are at higher risk for blood clots than women who are on the pill -- a blood clot occurs in one pregnant woman for every 1,000 to 1,500 pregnant women, while one in 3,000 women who take birth control pills experience some form of blood clot, according to the National Blood Clot Alliance.

Birth control pills contain a combination of estrogen and progestin, with progestin being the strongest agent in the contraceptive. Estrogen is added to offset some of the side effects of progestin. While previous studies found that estrogen increased some women's risk for blood clots, other studies suggested that, to a lesser degree, progestin could too.

But not all doctors are convinced.

Experts Say Birth Control Is Safe Overall

Dr. David Grimes, vice president of Family Health International, says he's not persuaded that either form of progestin -- drospirenone or levonorgestrel -- has been found to cause blood clots.

"These data are not credible. There's no biological basis on progestin causing blood clots," said Grimes. Grimes served as a member of the data safety monitoring committee at Bayer, which manufactures Yaz and Yasmin.

"They're barking up the wrong tree," he said.

Birth control pills are generally considered safe. But women who are obese, older than 35 and smoke, or who have a family history of blood clots, should not take oral contraceptives.

While the new studies published today make it difficult to determine the blood clot risk, doctors need to continue to inform their patients about any potential risk from any form of estrogen and progestin combination birth control pills, said Dr. Ricardo Azziz, a reproductive endocrinologist and researcher at Georgia Health Sciences University.

"It may be best to consider the data when choosing the first pill that a woman starts," said Azziz. Women respond to birth control pills differently. Some women experience weight gain, mood swings or spotting.

Birth control pills with drospirenone -- the newer progestin -- have been more frequently prescribed, because many women tolerate it better than the older progestin, said Streicher.

According to Azziz, women are more likely to continue taking the pill regularly if they find one that provides the least side effects or the best outcome.