Oral Contraceptive-Related Thrombosis
Blood clots associated with combined hormonal birth control
Quick Facts
- Type: Medication-related vascular condition
- Linked to: Combined (estrogen-containing) birth control
- Common sites: Leg veins (DVT), lungs (pulmonary embolism)
- Seek urgent care: Leg swelling, chest pain, sudden breathlessness
Overview
Combined hormonal contraceptives, including most birth control pills, contain estrogen and a progestogen. The estrogen component slightly increases the blood's tendency to clot. As a result, people taking these pills have a small but real increase in the risk of venous thromboembolism, which means clots forming in the deep veins (deep vein thrombosis) or traveling to the lungs (pulmonary embolism).
It is important to keep this risk in perspective. The overall chance of a clot on the combined pill is low, and is lower than the clotting risk during pregnancy itself. Progestogen-only methods, such as the mini-pill, the implant, and the hormonal IUD, are not associated with this increased clot risk. Understanding the warning signs and personal risk factors helps people choose contraception safely.
Symptoms
Symptoms depend on where a clot forms. A clot in a leg vein typically causes:
- Swelling, usually in one leg
- Pain or tenderness, often in the calf
- Warmth, redness, or discoloration of the skin
A clot that travels to the lungs is an emergency and may cause:
- Sudden shortness of breath
- Chest pain that worsens with breathing
- A fast heartbeat
- Coughing, sometimes with blood
- Lightheadedness or fainting
A sudden severe headache, vision changes, or weakness on one side could indicate a rarer clot affecting the brain and also need emergency care.
Causes
The increased clotting tendency comes mainly from the estrogen in combined contraceptives, which changes the levels of clotting proteins in the blood. The size of the risk depends on several factors.
- Estrogen dose and type of progestogen: Some formulations carry a slightly higher risk than others.
- Individual risk factors: Smoking, obesity, older age, and inherited clotting disorders add to the baseline risk.
- Timing: The risk is highest in the first months after starting or restarting the pill.
Progestogen-only contraceptives do not contain estrogen and are not linked to this increased clot risk, making them an option for people who need to avoid estrogen.
Risk Factors
- Smoking, especially over age 35
- Obesity
- A personal or family history of blood clots
- An inherited clotting disorder (thrombophilia)
- Prolonged immobility, recent surgery, or long-distance travel
- Certain migraines (migraine with aura) and high blood pressure
Diagnosis
A suspected clot is investigated the same way regardless of cause.
- Leg ultrasound: The main test for a suspected deep vein thrombosis.
- Blood test (D-dimer): Can help rule out a clot in lower-risk situations.
- Chest imaging: A specialized scan of the lungs if a pulmonary embolism is suspected.
Before prescribing the combined pill, clinicians also assess personal and family history to estimate clot risk and choose the safest method.
Treatment
A confirmed clot is treated with blood thinners, and the contraceptive is reviewed.
- Anticoagulants: Blood-thinning medication to treat the clot and prevent it from growing or recurring.
- Stopping the combined pill: The estrogen-containing contraceptive is usually stopped, and a non-estrogen method or non-hormonal option is chosen.
- Treating the immediate problem: A large clot in the lungs may require more intensive hospital treatment.
After a clot, people are advised to avoid estrogen-containing contraception in the future.
Prevention
- Discuss your full personal and family history with a clinician before starting the pill
- Consider progestogen-only or non-hormonal methods if you have clot risk factors
- Do not smoke, particularly if you are over 35 and using the combined pill
- Stay active and avoid long periods of immobility; move during long journeys
- Tell health professionals you take the combined pill before any surgery or long period of bed rest
When to See a Doctor
Stop the pill and seek emergency care if you develop signs of a clot, including:
- Swelling, pain, or warmth in one leg
- Sudden shortness of breath or chest pain when breathing
- Coughing up blood
- A sudden severe headache, vision loss, or weakness on one side
These symptoms can be life-threatening and need immediate medical attention. Tell the medical team you are using a combined contraceptive.
Frequently Asked Questions
Do birth control pills cause blood clots?
Combined pills containing estrogen slightly raise the risk of blood clots because estrogen increases the blood's clotting tendency. The overall risk is low, and it is lower than the clotting risk during pregnancy. Progestogen-only methods do not carry this increased risk.
Who should avoid the combined pill because of clot risk?
People who smoke and are over 35, those who are very overweight, and anyone with a personal or family history of blood clots or an inherited clotting disorder are at higher risk. They are often advised to use progestogen-only or non-hormonal contraception.
What are the warning signs of a clot on the pill?
Swelling, pain, or warmth in one leg can signal a leg clot, while sudden breathlessness, chest pain when breathing, or coughing up blood can mean a clot in the lungs. A sudden severe headache or weakness on one side also needs emergency care.
When is the clot risk highest on the pill?
The risk is highest in the first few months after starting or restarting the combined pill, and after periods of immobility such as surgery or long travel. It then settles to a lower steady level for ongoing users.
What contraception is safer if I have clot risk factors?
Progestogen-only options such as the mini-pill, contraceptive implant, hormonal IUD, and the copper (non-hormonal) IUD do not contain estrogen and are not linked to the increased clot risk. A clinician can help choose the safest method for you.
References
- Centers for Disease Control and Prevention (CDC). U.S. Medical Eligibility Criteria for Contraceptive Use.
- MedlinePlus, U.S. National Library of Medicine. Birth control pills.
- American College of Obstetricians and Gynecologists (ACOG). Combined hormonal birth control.