Newer Birth Control Pills Still Pose Risks of VTE

Oral contraceptives are known to increase a woman’s risk of blood clots particularly in the large veins in the legs. This is called venous thromboembolism (VTE), and it can be dangerous as well as painful. However, over the past several decades, the doses of hormones in birth control pills have dropped dramatically. Has that eliminated the risks of VTE?

Danish Scientists Study the Risks of VTE:

Danish researchers wondered if modern contraceptives are still associated with an increased risk for clotting. To find out, they analyzed the Danish national registers to study healthy females between 15 and 49 (JAMA, Feb. 10. 2025). The study lasted a decade and covered about 1.4 million women for about 8.5 million person-years. That is quite a lot of data. Not all of the contraceptives used were pills, although all contained either estrogen, progestin or both.

What Did the Investigators Discover About the Risks of VTE?

Rates for people not using hormonal contraceptives were about 2 in 10,000 person-years. Females taking combined estrogen and progestin pills had a rate of 10 per 10,000. Women using vaginal rings had a rate of VTE around 8 per 10,000. Patches had very similar risks of VTE, whereas progestin-only pills produced a rate of 3.6 per 10,000 person-years. The lowest rate among hormonal contraception users were for those with IUDs, at just 2.1 per 10,000 person-years. That is indistinguishable from the rate for individuals not using hormonal contraception.

The investigators concluded:

“Variation in VTE risk across products underscores the importance of personalized contraceptive counseling.”

What Did Older Studies Show?

Previous research showed more than a decade ago that birth control pills containing the progestin drospirenone raised the risks of VTE much more than older types containing levonorgestrel. Epidemiologists found that women taking pills like Yasmin, Yaz or Ocella were two or three times more likely to experience a clot than those taking pills such as Jolessa, Seasonale or Seasonique (BMJ, April 21, 2011).

The clots detected in that study were not deadly, but they can be quite dangerous. When blood clots lodge in the legs they cause deep vein thrombosis (DVT). It is a form of VTE. If those clots break loose and travel to the lungs they can cause pulmonary embolisms. Although the overall risk of such problems is low, otherwise healthy women should be informed about this potential danger from birth control pills.