Should I Worry About Blood Clots on the Pill? Real Risk, Real Numbers

Blood-clot statistics are useful only when the comparison is clear: which pill, which population, and over what period? This guide separates those questions so a small population risk is neither dismissed nor exaggerated.

What kind of blood clot are we discussing?

Venous thromboembolism (VTE) includes deep vein thrombosis (DVT), usually a clot in a deep leg vein, and pulmonary embolism (PE), a clot blocking a blood vessel in the lungs. Both need medical attention. This article concerns venous clots, not the separate risks of heart attack or stroke. NHS: DVT and pulmonary embolism.

Combined pills: absolute risk in context

The table uses the European Medicines Agency's estimates for the specified combined hormonal contraceptives. The numbers describe events among 10,000 women over one year, not the risk from one tablet.

Source: EMA combined hormonal contraceptive review. These are approximate estimates for the listed products, not a prediction for an individual or a complete ranking of every pill available today. Estrogen dose and personal risk factors also matter.

Different studies can produce different estimates. For example, a 2025 Danish cohort study reported a standardized rate of 10.0 VTE events per 10,000 person-years across combined-pill users, with variation between formulations. That study should not be mixed with another source to create a precise personal risk calculation.

Pregnancy and postpartum: why the time period matters

Pregnancy and the weeks after birth also increase clot risk, particularly after delivery. But pregnancy is not the only alternative to a combined pill: other contraceptive methods may be appropriate.

One English cohort study published in 2013 reported 99 VTE events per 100,000 person-years during pregnancy and 468 during the early postpartum period, using its restrictive case definition. Converted to the same denominator, these are 9.9 and 46.8 per 10,000 person-years.

These are annualized incidence rates, not the chance of a clot during a pregnancy or six weeks after birth. The study defined its early postpartum interval separately from the days around delivery, and risk changes over time. Differences in study populations and case definitions also limit direct comparisons with contraceptive estimates.

These figures provide context. They do not establish that every pill is safer than pregnancy for every person or override a reason to avoid estrogen.

What about progestin-only pills?

Progestin-only pills contain no estrogen. An updated systematic review of studies published through November 2022 generally found no increased VTE risk with these pills, but rated the evidence low or very low certainty. That review distinguished pills from the DMPA injection, for which it found a different risk signal.

A newer Danish study published in 2025 reported 3.6 events per 10,000 person-years among progestin-only pill users versus 2.0 among nonusers. This observational association does not by itself establish causation, but it is a reason to avoid saying the mini-pill has no clot risk.

Method choice should reflect your medical history and the specific product. CDC guidance for progestin-only methods treats pills, implants, and injections separately.

Personal factors to discuss with a prescriber

Tell your prescriber about previous DVT or PE, known thrombophilia, close relatives with clots, major surgery or prolonged immobility, recent childbirth, and other relevant health conditions. Obesity can also affect VTE risk. Smoking at age 35 or older raises important cardiovascular concerns with combined pills, including arterial events. CDC eligibility guidance explains how these circumstances affect contraceptive choices.

A previous clot often makes estrogen-containing contraception unsuitable, but recommendations depend on recurrence risk and anticoagulant treatment. Do not start, stop, or switch methods based on this article alone. Routine thrombophilia testing for everyone before starting contraception is not recommended by CDC.

Related guides: smoking and pill eligibility, migraine, and high blood pressure.

Symptoms: when to seek help

Possible DVT symptoms include pain, swelling, warmth, or a change in skin colour in one leg. Seek urgent assessment for a suspected DVT. NHS symptom guidance.

Sudden breathing difficulty, pain in the chest that worsens with breathing, or coughing up blood can signal a pulmonary embolism. Seek immediate medical help; call your local emergency number for severe breathing difficulty, chest pain, a very fast heartbeat, or collapse. Do not drive yourself if emergency care is needed. NHS emergency guidance.

Using records during a routine consultation