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Hormonal birth control and blood clots, explained

Hormonal birth control and blood clots, explained

6 min read

Like any prescription medication, all forms of hormonal birth control come with some possible risks — one of which you might have heard a lot about after the Johnson & Johnson's Janssen COVID-19 vaccine generated news in the spring of 2021: slightly increased risk of blood clots.

While the overall risk of blood clots is low for most people (with or without hormonal birth control), we're here to answer any questions you may have about this potential side effect — from why this can happen to the risk for different types of birth control to how to make the right decision for you.

Your takeaways

  • Blood clots occur to stop bleeding. But when they form for no reason, don't dissolve, block the flow of blood, or form in the leg, lungs, or brain, that's an issue.
  • All combined hormonal contraceptives are associated with slightly increased risk of venous thromboembolism — or blood clots in the veins. The risk increases a bit further for combined oral contraceptives containing drospirenone and the birth control patch.
  • The benefits of combined hormonal contraceptives likely outweigh the potential risks for most people. But if you have certain high-risk factors that make blood clots more likely, that will factor into the decision of what birth control is right for you.
  • Talk to your healthcare provider about finding the right birth control for you based on your individual risk factors, comfort level, and preferences.

What are blood clots?

When you have an injury or a cut, gel-like clumps of blood (clots) show up to plug the injured blood vessel and stop the bleeding. But when blood clots form for no reason, don't dissolve, block the flow of blood, or form in the leg, lungs, or brain, they become a problem.

Venous thromboembolism is a disorder of blood clots in the veins. Two types in particular are associated with hormonal birth control:

  • Deep vein thrombosis (DVT): a blood clot that forms in a deep vein in the lower leg, thigh, or pelvis (which can travel to the lungs).
  • Pulmonary embolism: a blood clot that travels through to the lungs.

The extremely rare blood clot (2-3 cases in 100,000 people) associated with the J&J/Janssen COVID-19 vaccine is neither of these — it's what's known as thrombosis with thrombocytopenia syndrome (TTC), or blood clots combined with low platelets. According to the CDC, people who use oral contraceptives are not more likely to develop TTS after getting the J&J/Janssen vaccine, and there's no recommendation that people should stop taking hormonal birth control before or after getting the shot. The CDC does recommend that people with ovaries, regardless of whether or not they're using hormonal birth control, know about the increased risk of TTS with the J&J/Janssen vaccine.

Does taking hormonal birth control increase the risk of blood clots?

According to the American College of Obstetricians and Gynecologists (ACOG), all forms of combined hormonal contraceptives have been associated with a slightly increased risk of venous thromboembolism. Combination birth control pills containing the progestin (a synthetic form of progesterone) drospirenone, as well as the birth control patch, may increase the risk further. But it's important to remember that the overall risk remains very low.

As we'll get into a little later, estrogen is the reason combined hormonal contraceptives have slightly increased risk of blood clots. But let's talk about drospirenone for a moment: According to OB-GYN and Modern Fertility medical advisor Dr. Eva Luo, MD, MBA, FACOG, the birth control pill Yasmin/Yaz "illuminated the increased clot risk with drospirenone." But the reality is that most people won't know exactly what type of progestin is included in a combined oral contraceptive. That said, Dr. Luo explains that some people might express interest in Yaz because of benefits like improvements with acne. Despite the specific increased risk linked with drospirenone, Dr. Luo says she discusses and screens for blood clot risk factors for anyone who's considering a birth control that includes estrogen.

Let's put all of these risks into perspective:

  • ~1-5 out of 10,000 nonpregnant people who are not on combined oral contraceptives (the birth control pill) may experience venous thromboembolism.
  • ~3-9 out of 10,000 people with ovaries who are on combined oral contraceptives may experience venous thromboembolism.
  • 7.8 out of 10,000 people with ovaries who are on the vaginal ring may experience venous thromboembolism.
  • 9.7 out of 10,000 people with ovaries who are on the birth control patch may experience venous thromboembolism.
  • ~10 out of 10,000 people with ovaries who are on oral contraceptives with drospirenone may experience venous thromboembolism.
  • ~5-20 out of 10,000 pregnant people may experience venous thromboembolism.
  • ~40-65 out of 10,000 people in the postpartum period may experience venous thromboembolism.

Overall, the risk of venous thromboembolism while on combined hormonal contraception is still very low — and quite a bit lower than the risk level seen in pregnancy or during the postpartum period. But there are also types of hormonal birth control that don't increase the risk of blood clots: A 2012 meta-analysis saw no increased risks with the hormonal intrauterine device (IUD) and progestin-only minipill. (A 2016 meta-analysis backs up these findings.)

It's important to talk to your healthcare provider about your history or any family history with blood clots so you can get birth control recommendations that make the most sense for you.

How does hormonal birth control increase the risk of blood clots?

Combined contraceptives can increase fibrinogen (a protein that's essential for blood clotting) and raise the likelihood of hypercoagulability — or clotting when there's no bleeding. "Hypercoagulability is primarily driven by estrogen, so the clot risk is not isolated to pills, but extends to the patch and ring," says Dr. Luo. "It's really only in the case with drospirenone that the combination of the two seems to be a bit more potent than estrogen alone — we see very little hypercoagulability risk with progestins in general."

Explained another way, estrogen is the main cause of the slightly increased risk of blood clots with combined hormonal contraceptives. Estrogen + drospirenone increases the risk further, but progestin doesn't increase the risk on its own.

Is there anyone with a greater risk of blood clots while on combined hormonal contraceptives?

ACOG explains that some of the high-risk factors for blood clots a healthcare provider will take into account before prescribing certain types of hormonal birth control include:

  • Smoking if you're over age 35
  • <21 days postpartum (or 21-42 days postpartum with other risk factors)
  • Major surgery that leaves you immobile
  • A history of DVT or pulmonary embolism
  • Hereditary thrombophilia (a blood-clotting disorder)
  • Severe inflammatory bowel disease
  • Systemic lupus erythematosus with positive (or unknown) antiphospholipid antibodies (this is also a known risk factor for all forms of hormonal birth control other than the IUD)

Combined hormonal contraceptives (including the pill, ring, and patch) are not recommended for people with the above high-risk factors. For people without these high-risk factors (or others unrelated to blood clots), the benefits likely outweigh the potential risks. If people who do have these risk factors are still interested in oral contraceptive pills, Dr. Luo says progestin-only forms of birth control are fine to use — including Slynd, a progestin-only pill that contains drospirenone. Non-hormonal birth control methods (like the copper IUD) or barrier methods (like condoms) are also always options.

Are there any signs of blood clots to look out for if you're on combined hormonal contraceptives (or even if you're not)?

Knowing about the potential risks of any medication can make it easier to be aware and seek out medical help if something happens. Here's what to be conscious of in regard to the signs of blood clots in particular:

Dr. Luo adds that situational factors like having sat for a prolonged period of time while traveling, recently having surgery, recently being pregnant or postpartum, or recently having a cancer diagnosis can increase the risk of a blood clot. The signs highlighted above are even more important to pay attention to if any of these factors are relevant for you.

Blood clots and birth control: Is there a bottom line?

It's always important to talk about your personal health history and known family history when discussing contraceptive options with your healthcare provider. If you have one of the conditions that increase the risk of blood clots on its own, you can talk to your provider about non-hormonal or progestin-only methods. If you don't have those high-risk factors (or others unrelated to blood clots), the benefits of combined hormonal contraception may outweigh the potential risks.

There's a lot to consider when choosing birth control, and no one can make that decision other than you and your healthcare provider. For more on different birth control options and associated benefits and risks, check out the "Birth control" section of the Modern Fertility blog. We're always here to help you make the most informed and empowered choices about your fertility.

This article was medically reviewed by Dr. Eva Marie Luo, MD, MBA, OB-GYN at Beth Israel Deaconess Medical Center and Clinical Lead for Value at the Center for Healthcare Delivery Science at Beth Israel Deaconess Medical Center.

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Chanel Dubofsky

Chanel's writing has appeared in Cosmo, Rewire, Lilith, HelloFlo, & Extra Crispy. She has an MFA in Fiction from Vermont College of Fine Arts & lives in New York. Follow her @chaneldubofsky.

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