Oral Contraceptive-Related Thrombosis (Blood Clots From the Pill)

How the pill affects clotting

Estrogen, especially ethinyl estradiol, increases the liver's production of clotting factors and reduces natural anticoagulants. This tips the balance toward clotting. The type of progestin combined with estrogen also affects risk, and higher estrogen doses raise risk.

Progestin-only methods (mini-pill, implant, hormonal IUD) do not meaningfully raise clot risk. The injection (DMPA) may slightly raise it.

How big is the risk?

Approximate yearly risk of a venous clot per 10,000 women:

Risk is highest in the first 3 to 12 months after starting or restarting a combined method after a break of 4 weeks or more.

Risk factors that add to the pill's effect

• smoking, especially over age 35
• obesity, particularly BMI of 30 or more
• age over 35
• inherited thrombophilia such as factor V Leiden, prothrombin mutation, or antithrombin, protein C or protein S deficiency
• personal or family history of blood clots, especially in a parent or sibling before age 50
• recent surgery, injury or immobility, including long-haul flights
• the first 6 weeks after childbirth
• certain conditions: lupus with antiphospholipid antibodies, cancer, inflammatory bowel disease

Estrogen methods also slightly increase the risk of arterial clots (heart attack and stroke), mainly in people who smoke, have high blood pressure, diabetes with complications, or migraine with aura.

Warning signs: ACHES

• Abdominal pain (severe)
• Chest pain, breathlessness or coughing up blood
• Headaches (severe or sudden)
• Eye problems: blurred vision or loss of vision
• Severe leg pain or swelling, usually in one calf or thigh

Signs of a deep vein thrombosis include pain, swelling, warmth and redness in one leg. Signs of a pulmonary embolism include sudden breathlessness, chest pain and a fast heartbeat.

Diagnosis

• Doppler ultrasound of the leg for DVT
• CT pulmonary angiogram for pulmonary embolism
• D-dimer blood test to help rule out clots in lower-risk situations
• MRI or CT venography for cerebral venous thrombosis
• Thrombophilia testing in selected cases, such as clots at a young age or a strong family history

Treatment

• stop the estrogen-containing method and switch to a non-estrogen option
• anticoagulants such as apixaban, rivaroxaban, low-molecular-weight heparin or warfarin, usually for at least 3 months
• treatment in hospital for large pulmonary emboli or clots in the brain's veins

Because some anticoagulants can cause heavier periods and harm a developing baby, reliable non-estrogen contraception, such as a hormonal IUD, is recommended during treatment.

Who should not use estrogen-containing contraception

According to US Medical Eligibility Criteria, combined methods are generally not recommended for people with:

• a current or past blood clot, or known high-risk thrombophilia
• smoking 15 or more cigarettes a day and age 35 or over
• migraine with aura
• uncontrolled high blood pressure
• major surgery with prolonged immobilization
• less than 3 to 6 weeks after childbirth, depending on other risks
• certain heart, liver and autoimmune conditions

Reducing your risk

• choose a lower-risk combined pill (levonorgestrel or norethisterone) if you use one
• consider progestin-only or non-hormonal methods if you have risk factors
• do not smoke
• stay active, and move regularly on long flights and car trips
• tell your doctor you take the pill before surgery; it may be stopped 4 weeks before major operations

Frequently asked questions

How likely is a blood clot on the birth control pill?

The risk is low. About 5 to 12 out of 10,000 people using a combined pill develop a clot each year, compared with about 2 in 10,000 who do not use hormones. Pregnancy carries a higher risk than the pill.

Which birth control has the lowest blood clot risk?

Progestin-only methods, including the mini-pill, implant and hormonal IUD, and the non-hormonal copper IUD do not meaningfully raise clot risk. Among combined pills, those with levonorgestrel or norethisterone have lower risk than those with desogestrel, gestodene or drospirenone.

What are the warning signs of a blood clot on the pill?

Remember ACHES: severe abdominal pain, chest pain or breathlessness, severe headaches, eye problems such as vision loss, and severe leg pain or swelling. Seek emergency care for any of these.

Can I take the pill if blood clots run in my family?

If a parent or sibling had a clot, especially before age 50, talk to your doctor before using estrogen. You may be advised to use a progestin-only or non-hormonal method, or to have testing for inherited clotting disorders.