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Which Birth Control Pill Is Safest?

Researchers Find Differences in Blood Clot Risk in Different Oral Contraceptives
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WebMD Health News
Reviewed by Louise Chang, MD

Aug. 13, 2009 -- When it comes to the risk of blood clots, some oral contraceptive pills are safer than others, according to new studies by European researchers.

"Oral contraceptives with levonorgestrel and a low dose of estrogen are associated with the lowest risk of venous thrombosis [blood clots] and are therefore the safest option," says Astrid van Hylckama Vlieg, PhD, a research fellow at Leiden University Medical Center in the Netherlands, and the lead author of one study.

''Our study shows that there is indeed a difference in the risk of venous thrombosis associated with different types of progestins and different doses of estrogens available in the contraceptive," she tells WebMD in an email interview.

Similar results were obtained in the second study, evaluating Danish women. Both studies are published in the online edition of BMJ.

Even with differences in risk, however, a U.S. expert who reviewed the studies for WebMD points out that the differences are small and the overall risk of getting a blood clot from the pill is very low to begin with.

The risk of blood clots associated with birth control pill use has been known for decades, with several studies finding a twofold to sixfold increased risk with the use of oral contraceptives. The new research confirms earlier findings and adds new specifics about which hormones carry the most risk.

Birth Control Pills and Blood Clots

Van Hylckama Vlieg and colleagues compared 1,524 women, ages 18 to 50, diagnosed with a first deep venous thrombosis (DVT) of the leg, which is a blood clot in the leg, or a pulmonary embolism, a blood clot in the lung, and compared them with 1,760 healthy people. 

Women taking oral contraceptives had a fivefold increased risk of blood clots compared with nonusers, and the risk differed by the type of progestin. "The newer types of oral contraceptives containing drospirenone or cyproterone acetate are associated with an increased risk compared with oral contraceptives containing levonorgestrel," Van Hylckama Vlieg says. Specifically, the researchers found that:

  • Levonorgestrel boosted the risk of blood clots by nearly fourfold compared to nonusers.
  • Gestodene boosted risk by 5.6 times.
  • Drospirenone boosted risk 6.3 times.
  • Cyproterone boosted risk 6.8 times.
  • Desogestrel boosted risk 7.3 times.
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