Updated on June 25, 2024.
If you’re among the 14 percent of women aged 15 to 49 in the United States who currently take birth control pills, you may be at risk of developing a blood clot. But there are many types of birth control pills and very different risk levels, depending on your health situation. Here’s what to know about birth control pills and blood clots.
The role of blood clots
Blood clots are your body’s way of healing itself. When you get cut or injured, your body starts to form blood clots. These are little clumps of blood that feel sort of like gel. They stop the bleeding by sealing up the wound so that healing can begin.
But in rare instances, blood clots can form inside the veins, plugging up the flow of blood. This is called venous thromboembolism (VTE). It can lead to serious health issues. VTEs include:
- Deep vein thrombosis (DVT): This is a blood clot that occurs in a vein, usually in the legs.
- Pulmonary embolism: This is when a blood clot dislodges and travels to the lungs, where it can get stuck in an artery. This can cause a potentially fatal blockage.
These kinds of clots need immediate medical attention. Some forms of hormone therapy, including birth control pills, can slightly raise the risk of VTE.
Estrogen
A common ingredient in contraceptive pills and in hormone replacement therapy, estrogen can be very useful. But estrogen can sometimes affect proteins in the blood and cause it to be more likely to clot. This can raise the risk of blood clots forming in the legs or in the blood vessels that move blood from the lungs to the heart.
Estrogen is usually used in combination with progesterone in birth control pills. Until the 1990s, estrogen was thought to be the cause of all blood clots related to contraceptive use. But starting in 1995, researchers began to find evidence that newer types of progesterone were also contributing to this risk.
Progesterone
Your body naturally makes progesterone. It helps build up the lining of the uterus and prepare it for a potentially fertilized egg during the menstrual cycle. It’s also an ingredient in combination birth control pills, or pills that contain both estrogen and progesterone.
Progestins are human-made forms of the hormone progesterone. Progestin-only contraceptives do not seem to increase the risk of blood clots. However, newer forms of the hormone progesterone may raise the risk of blood clots when combined with estrogen. The current evidence for this is somewhat uncertain. Some studies show an increased risk while others do not, according to a 2022 review published in the journal Research and Practice in Thrombosis and Haemostasis.
Still, the American College of Obstetricians and Gynecologists (ACOG) states that combined hormonal methods that include a progestin known as drospirenone can slightly raise the risk of DVT.
Symptoms of blood clots
Sometimes, blood clots do not have symptoms. It depends on where in the body the clot forms, and how much it blocks the flow of blood. Symptoms of clots that form in the legs, chest or arms may include:
- Sharp pain in the chest or calf
- Shortness of breath
- Coughing up blood
- Uneven or faster than usual heartbeat
- Weakness or numbness in the arms or legs
- Swelling, pain, or skin color changes in the leg
If you experience any of these symptoms, call 911 or go an emergency room right away.
What to know about risk of clots
Though birth control pills do carry some added risk for blood clots, it’s quite small. The overall risk of VTE related to oral birth control pills is not much higher than the risk for people not on any form of birth control. And it’s actually lower than for those who are pregnant.
Hormonal birth control causes VTE in up to 10 people in every 10,000 each year. People who aren’t on birth control experience clots at a rate of about 1-5 people per 10,000 each year. And the rate of clots among pregnant people is about 10 to 20 per 10,000 people each year. And for some, the medical benefits of taking hormone therapies far outweigh potential harms.
Recent research has suggested that transgender women who are on hormonal treatment may have an increased risk of VTE compared to cisgender women or men. More studies are needed, but if you have a history of VTE and are transgender, be sure to discuss alternative hormone therapy approaches with your healthcare provider (HCP). Transdermal estrogen may be a safer method of hormonal therapy. It is absorbed through the skin and comes in sprays, gels, and patches.
The best birth control method for you
If you take birth control pills or are interested in starting or switching to a new method of birth control, discuss the risks and benefits with your HCP. Be open about your medical history and habits so they can assess your individual risk for VTE.
Smoking, having a family history of blood clots, being overweight, being 35 or older, or having a history of stroke, migraine with aura, ischemic heart disease, or other cardiovascular diseases can all make you more susceptible to clotting. Speak with your HCP to ensure you’re prescribed the safest form of birth control for your situation.
