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Blood Clots and Birth Control

Updated: Nov 15, 2022

I have been on various forms of birth control for almost 10 years now, and the first time I heard about the increased risk of developing a blood clot from birth control was about 7 years in. It was when I was attending an assembly meeting to prepare for my exchange program in Europe. A lady told all the women in the audience to remember to get up every hour or so on long flights or buses to walk around to prevent blood clots from forming. I nudged my friend to see if she was hearing what I was hearing. Why was I just learning about this now? After being on birth control for years, I was confused and concerned, to say the least. Not to mention how curious I was to know just how important this advice is and if I should really be taking it seriously.

I know I’m not alone in saying that I felt very lost and uninformed while choosing a birth control method, and even more uninformed when deciding which birth control method is best suited for me. After doing some research on my own of risk factors associated with various types of birth control, I feel more confident moving forward. In today’s world of hormonal birth control, the risk of developing dangerous blood clots exists, but is low. Nonetheless, it is important to be aware of the genetic and environmental factors that can act to increase the risk. So let's chat about them!

What are blood clots?

These two words have been thrown around quite a bit lately with the release of the COVID vax, so let’s first get the definition straight.

Blood clotting, or coagulation, is an important process that our bodies naturally do to prevent excessive bleeding when a blood vessel is injured. Typically, the blood clot will dissolve on its own. Sometimes, however, a blood clot can form without injury or does not dissolve naturally. This can prevent proper blood flow in the body and result in pain and swelling. In some women, the use of hormonal birth control can increase the risk of developing a blood clot in the veins, known as venous thromboembolism (VTE), more commonly in the leg, known as deep vein thrombosis (DVT) or in the lung (pulmonary embolism, PE). It is possible for a blood clot to detach from its original location and travel towards the lungs as well.

Why does birth control increase the risk of blood clots?

There are two common hormones that most hormonal birth control methods contain. Estrogen, which is a naturally occurring hormone in the body (in birth control it’s generally Ethinyl Estradiol), and progestin, which is a synthetic version of progesterone, another naturally occurring hormone. The reason why hormonal birth control can increase the risk of blood clotting is because estrogen and progestin have an effect on the anti-coagulation (anti-blood clot) pathway that naturally occurs. Specifically, estrogen increases the levels of clotting in the body. If you want to get more technical with it, this pathway we are talking about is called the Tissue Factor Pathway Inhibitor (TFPI).

Methods of birth control and associated risk

Most forms of hormonal contraceptives contain either a combination of both estrogen and progestin or progestin alone.

Progestin only

Progestin only contraceptives can be administered orally (the mini-pill), by injection (the shot), or as an implantable device (the implant). All three of these methods have been thoroughly investigated and results suggest that the progestin-only contraceptives have little to no statistically significant association with VTE (aka: blood clots). IUDs that contain levonorgestrel (a type of progestin), such as Mirena, Liletta, Skyla, and Kyleena are not associated with elevated risks of VTE (CITE) either.

All in all, if you are at higher risk for blood clotting, progestin only options are generally the safest route to go when it comes to hormonal contraceptives. Chat with your doctor to assess your risk and to see if progestin only methods are the most suitable for you or not.


The birth control methods that contain both estrogen and progestin are referred to as combination contraceptives. These are the options to watch out for.

Combination birth control methods are associated with a risk of developing blood clots. Okay, but don’t panic! The association varies depending on the type and doses of estrogen and progestin and still the absolute risk is pretty low.

The first generation of combination contraceptives that contained high doses of both hormones and were linked to various health issues, VTE included. For that reason, these pills are no longer available. Over time, 3 more generations of combination contraceptives were introduced, all with different levels of risk. Out of the 4 generations of combination contraceptives, the second generation are considered the safest, with the lowest risk of developing blood clots. Generally out of 10,000 people taking hormonal birth control 3 -9 women will develop blood clots in a year. Some 3rd and 4th generation progestins have a slightly higher associated blood clot risk. These are desogestrel, cyproterone and drospirenone. Newer is not always better! If you choose to use a combination contraceptive, it is a good idea to ask your pharmacist or doctor what progestin is in your birth control.

Just one more thing to add to the mix: combination contraceptives such as vaginal rings and the patch carry a 6-8x greater risk. The added risk could be because the hormones are constantly being released.

Other factors

It is important to remember that these methods of birth control increase the risk, not cause dangerous blood clots. Although the risk numbers are high, the absolute risk is low. Think, only less than 10 people out of 10,000 using combination birth control develop blood clots in a given year.

There are various other factors that play a role in why someone might develop VTE.

1. Genetic factors – personal or family history of blood clots

  • Without a genetic test, neither the patient nor doctor is aware of the genetic predisposition that could factor into the risk of developing DVT. A family history of VT could be an indication of genetic risk, so keep this in mind when choosing a birth control!

2. Pregnancy

  • This is basically because a pregnant person's body coagulates more easily to try and prevent excessive blood loss during labour (ok kind of cool though). Developing a blood clot during pregnancy can be prevented with close monitoring if you are at higher risk. Chat to your doctor!

3. Obesity

  • Obesity promotes a state of chronic inflammation that activates prothrombotic signaling pathways and this contributes to thrombotic risk in people with obesity.

4. Surgery

  • Basically this has to do with the inactivity of your muscles during and post surgery which causes limited blood flow and can cause blood to collect in your lower body.

5. Coagulation disorders

  • Any coagulation disorder where your body is clotting too much or too often.

6. Inactivity

  • Such as travelling long distances and remaining in positions that limit blood flow for long periods of time (aka: intercontinental cramped economy flights)


Don't worry, but do your research. And talk to your medical professional! If you find you are at a higher risk given any of the above factors, there are plenty of birth control options that you can still safely use. Try progestin only options, or non-hormonal ones like the Fertility Awareness Method and condoms. The good thing is you have options.

Had I known that sitting on a plane might not be as scary as that woman made it out to be (given my low risk overall and the type of birth control I was on), I may have had a nicer nap.

Editors: Lisa Hou, Dallas Barnes


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