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If you’ve ever paused before starting birth control because of something you heard about potential side effects, you’re not alone. Questions about side effects are among the most common concerns I hear, and blood clot risk is among the most misunderstood.
I work at a university student health center, where I see a lot of young women choosing a method for the first time. Many already ask about nonhormonal options. I understand the instinct, and I’d like to see more balance between nonhormonal and hormonal choices for both women and men.
My goal here isn’t to talk you into any one form of birth control. It’s to help you understand your options, which risks matter most, and what to discuss with your healthcare provider.
Not All “Hormonal Birth Control” Is the Same
“Hormonal birth control” isn’t one single thing. Combined hormonal methods, including most pills, the patch, and the vaginal ring, contain both estrogen and a progestin. Other hormonal methods contain progestin only, including the progestin-only pill, the implant, hormonal IUDs, and the birth control shot. Nonhormonal options include the copper IUD and barrier methods. [1] [2] [3]
One of the most serious side effects that can occur with combined hormonal contraception: blood clots. The increased risk for clotting is tied to estrogen-containing methods, while progestin-only and nonhormonal methods are considered lower risk. [1] [3]
How Estrogen Affects Clotting
Your body clots blood to protect you while keeping unnecessary clots from forming. Estrogen can shift the balance of proteins in that system, making blood somewhat more prone to clotting. The clots of greatest concern fall under the term venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). A DVT is a clot that typically forms in the deep veins of a leg or arm. If part of a DVT travels to your lungs, it becomes a PE, a potentially life-threatening event. [4] [5]
Taking an estrogen-containing method doesn’t mean you’ll develop a clot. Combined hormonal contraception generally brings a three- to five-fold increase in clot risk compared with nonuse, and that risk climbs further with added factors like smoking, obesity, or age. This risk increases dramatically if someone also has an underlying clotting disorder, such as factor V Leiden. [4] [6] [7]
Putting the Risk in Perspective
“Birth control increases clot risk” is true, but it leaves out important context. How much does the risk increase, for whom, and what does that risk actually mean? At a population level, the absolute risk is low for a healthy woman with no other risk factors, but “low” isn’t zero, and a clot can be serious or even fatal. To put numbers to it: each year, about 1 to 5 in 10,000 women who are neither pregnant nor using hormonal birth control develop a clot. For women using combined hormonal birth control, it’s about 3 to 9 in 10,000. During pregnancy, it’s about 5 to 20 in 10,000, and in the first 12 weeks after delivery it rises to about 40 to 65 in 10,000. That’s why individual risk factors matter, and why a population statistic should never replace a real conversation about your own history. The estrogen dose, the specific progestin, and your health background can all shift that number. [4]
Putting clot risk in perspective also means looking at the full range of possibilities. Pregnancy, particularly the weeks following delivery, is associated with a higher clot risk than combined hormonal contraception. At the same time, combined hormonal contraception is not the only way to prevent pregnancy. Progestin-only methods and nonhormonal options, including the copper IUD and barrier methods, do not carry the same estrogen-related risk and are options worth discussing. The goal isn’t to steer you toward any one method, but to make sure you understand the tradeoffs and can make an informed choice. [3] [4]
What Makes Your Own Risk Different
Before I prescribe a combined hormonal method, I ask whether a parent, sibling, or other close relative had a blood clot at a young age or without a clear cause. I also ask about smoking, age, weight, recent childbirth, recent surgery, prolonged immobility, and other health conditions. Some of these factors may make an estrogen-containing method inadvisable, while others matter more in combination. Estrogen can also slightly raise the risk of clots in arteries, which can cause a stroke or heart attack. That’s why I also ask about migraines with aura and high blood pressure, and why smoking matters even more after age 35. [3] [7]
That said, history has its limits. Some women who develop a clot have no known personal or family history, and not everyone knows the details of their family’s health. Current guidelines do not recommend routine genetic clotting disorder testing for every woman before starting birth control. If your personal or family history raises concern, ask whether testing or a specialist consultation would be useful in your case. Testing has limitations and is most helpful when the result would affect your care. [3]
Questions to ask when birth control is prescribed: Does this method contain estrogen? Does my history change what’s safe for me? Are there progestin-only or nonhormonal options that would work as well? What symptoms or side effects require urgent or emergency medical care? After starting a method, tell your healthcare provider about important changes, including an upcoming surgery, prolonged immobility, a new diagnosis, or the development of migraines or high blood pressure. [1] [3]
Warning Signs to Know
A DVT or PE can be life-threatening, and symptoms are sometimes subtle or even absent, which is exactly why it’s worth knowing the signs and taking them seriously. [5]
DVT symptoms:
- Swelling in one leg or arm
- Pain or tenderness you can’t explain by injury
- Warmth, redness, or discoloration of the skin
Seek prompt medical attention if you experience any of these symptoms.
PE symptoms:
- Sudden shortness of breath
- Chest pain that worsens with a deep breath
- An unexplained cough, especially coughing up blood
- A racing or irregular heartbeat, lightheadedness, or fainting
Treat any possible PE symptoms as a medical emergency. Don’t wait it out. If you raise these symptoms and feel dismissed, continue advocating for yourself and ask whether a blood clot is being considered. If symptoms persist or worsen, seek immediate reevaluation or emergency care. [5] Tell the medical team you use birth control and which method, since it affects how they assess you.
Making the Choice That’s Right for You
Choosing a safe method starts with an honest look at your personal and family history, a clear explanation of the estrogen-related clot risk, and your informed decision about how to move forward. From there, the right method also needs to fit your lifestyle, meaning it is effective, well tolerated, accessible, and aligned with what you want.
For some women, after that full risk conversation, an estrogen-containing method is the right fit. For others, including many young women who ask me about nonhormonal options up front, a progestin-only or nonhormonal method, with no estrogen-related risk, is the better answer. Either can be right, but only after a real conversation about your health history, not in place of one.
Estrogen keeps showing up at different points in your life, including with contraception, fertility care, pregnancy, and eventually menopause. Understanding its link to clotting now gives you a foundation for those conversations. This isn’t about creating fear or offering blanket reassurance. It’s about taking the risk seriously, knowing your history, understanding your options, watching for warning signs, and having a real seat at the table in your own care.
About the Author:
Vian Nguyen, MD, FACOG, is a board-certified OB/GYN who practices at the University of Houston Student Health Center, where she sees many young women navigating contraceptive choices for the first time. She also serves as Medical Advisor to the Rowan Foundation, a nonprofit organization dedicated to advancing awareness about women’s health and clotting.
