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Study: Newer Birth Control Pills May Double Blood Clot Risk

Overall Risk Is Still Low, but May Be Highest During the First Few Months of Use

FDA Investigation

The study, which is published in BMJ, comes as the FDA is reviewing the safety of newer birth control pills.

That investigation, announced in May, was scheduled to be finished by the end of summer.

In September, the agency said it had not yet reached a conclusion but “remains concerned about the potential increased risk of blood clots with the use of drospirenone-containing birth control pills.”

A panel of experts is scheduled to meet in December to discuss the findings of an FDA-funded study that evaluated the risks of blood clots in women who used several different hormonal birth control products.

Industry Responds

Bayer, the maker of Yaz, Yasmin, Ocella, and Beyaz, presented this statement to WebMD regarding the research:

“This study represents a reanalysis of the retrospective cohort study of Lidegaard et al., initially published in 2009 investigating the risk of venous thromboembolism (VTE) of combined oral contraceptives (COCs).  Bayer is currently evaluating this publication and cannot comment at this time.  

“Clinical data from a period of more than 15 years and up to 10 years of post-marketing safety study results support Bayer’s assessment that its drospirenone-containing COCs are safe and effective when used as indicated and that the risk of VTE is similar to any other low-dose estrogen COC studied, regardless of the progestogen.”

Advice to Women

“This is one of several studies that have shown that certain birth control pills have higher risks of blood clots over other birth control pills,” says Jennifer Wu, MD, an obstetrician/gynecologist at Lenox Hill Hospital in New York City, who was not involved in the research.

 “I think women really need to talk with their doctors before they start a birth control pill, and doctors should try to choose ones that have lower risks,” Wu says. “I wouldn’t start with these riskier oral contraceptives as first-line, first-start pills.”

Because so many women take birth control pills, even small risks can have significant public health consequences.

“You have to consider that 200 million women, every day, worldwide take such a pill. So even if it’s only one in 500 per year who get the thrombosis if they are on a fourth-generation pill and are 30 years old, then you actually get a relatively high number of complications,” says researcher Ojvind Lidegaard, MD, professor of obstetrics and gynecology, Rigshospitalet at the University of Copenhagen, in Denmark. “And you could actually halve that number just by changing the pill from a fourth- to a second-generation pill.”

But experts say switching to an older pill may not be the best option for every woman.

“It is important to have a range of different oral contraceptives available because some women tolerate one preparation better than another,” Philip C. Hannaford, MD, who is the Grampian Health Board chair of primary care at the University of Aberdeen, in Scotland, says in an email to WebMD.

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