Does HRT cause blood clots?
Last reviewed July 6, 2026 by Dr. Sapna Jadhav, General Physician. Sources from ACOG, NHS, Mayo Clinic, CDC, NICE, NIH, Cochrane, and peer-reviewed journals.
Bottom lineOral HRT tablets roughly double blood clot risk (from about 1-2 to 2-4 cases per 1,000 women per year) because swallowed estrogen stimulates the liver's clotting factors, but patches, gels, and sprays bypass the liver and show little to no added risk - making transdermal delivery the default choice, especially with any clot risk factor.
HRT tablets roughly double the risk of blood clots - but patches, gels, and sprays show little to no added risk, which makes this the most avoidable risk in all of HRT.
Why the delivery route matters
Estrogen swallowed as a tablet passes through the liver first, where it increases the production of clotting factors. Estrogen absorbed through the skin enters the bloodstream directly, bypassing the liver - and the clotting effect largely disappears.
- Oral HRT: venous thromboembolism (DVT and pulmonary embolism) risk roughly doubles - in absolute terms, from about 1-2 cases per 1,000 women per year to about 2-4.
- Transdermal HRT (patch, gel, spray): observational studies consistently show little or no increase in clot risk, even in women with risk factors.
For comparison: pregnancy raises clot risk more than oral HRT does.
What this means in practice
- Transdermal is the default choice in modern guidance, especially if you have any clot risk factors: a raised BMI, smoking, a family history of clots, reduced mobility, or migraine.
- A personal history of DVT, pulmonary embolism, or stroke generally rules out oral HRT; transdermal may still be possible with specialist input.
- The progestogen component matters too - micronized progesterone appears more clot-neutral than some older synthetic progestogens.
Know the warning signs
Seek urgent care for: a painful, swollen, or warm calf; sudden breathlessness; chest pain that worsens on breathing; or coughing up blood. Clots on HRT are rare, but these symptoms always warrant immediate assessment.
This is general information, not medical advice. Read the full evidence review: the risks of HRT.
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