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Prism Blog, Self Care for Trans Health

Estrogen and Blood Clot Risk in Trans Women

Estrogen produced by the body lowers blood concentrations of several clotting factors and speeds the rate at which clots dissolve. Estrogen also suppresses production of a factor which is involved in enlarging the size of a clot, and is also beneficial to cholesterol levels. (This may be why cisgender men are about 18% more likely to develop DVT than cisgender women.)

Administered estrogen, however, actually increases plasma fibrinogen, the activity of coagulation factors, and platelet activity. This explains why estrogen medications increase blood clots (in both transgender women and cisgender women taking birth control or hormone replacement therapy). Oral estrogen also significantly increases “bad” cholesterol in trans women, while decreasing the level of “good” cholesterol, which can lead to clogged arteries, increasing chances of clots.

Highest risk: Combining antiandrogens (like spironolactone) with oral ethinyl estradiol (birth control pills) carries a much higher risk of thrombosis than any other regimen. Trans women taking birth control pills are 20 times more likely to suffer from DVT than the general population. Premarin also carries a higher risk of DVT than injectable estrogen, though not as high as birth control. This is most often the case for hormones that are procured without a prescription. Prescribed HRT for trans women in the U.S. usually includes spironolactone and 17-beta estradiol (aka micronized estradiol), rather than ethinyl estradiol. This regimen is much less likely to produce clots.

Other risk factors: lack of exercise, long periods of immobility (such as long airline flights), genetic clotting risk, injuries (broken bones especially), liver stress (support liver while taking hormones!), high blood pressure, type 1 diabetes. Aspirin therapy is often recommended if over age 40 because of increased plasma concentrations of coagulation factors. Smoking increases factor XIII, thrombin, and fibrinogen, which increase clotting risk. Smokeless nicotine does not carry the same risk, and abstention from smoking for a period of only 2 weeks significantly decreases the rate of fibrinogen synthesis. Risk is highest within the first year of estrogen use, potentially because oral estrogen is more common than injectable estrogen during this time.


  • Using injectable rather than oral estrogen of any kind (if using oral estrogen make sure it’s 17-B estradiol)
  • Taking baby aspirin for the first year of HRT if over age 40
  • Supporting your liver metabolism
  • Exercise regularly
  • Quit smoking (or switch to smokeless tobacco for at least the first year of HRT)
  • Test for genetic clotting risk
  • Check blood pressure regularly and maintain safe levels

Symptoms of DVT: inexplicably warm area on your lower leg which persists for more than an hour, localized swelling, redness, pain, shortness of breath, chest pain, symptoms of stroke. CALL 911!

All information in this blog is for educational uses only. Always consult your doctor before taking any herbs or supplements, or changing or discontinuing your medications.

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Deep Vein Thrombosis and Hormone Use

A Personal Story: bloodisthickerthanwaterr.wordpress.com/2015/01/13/my-blood-clot-story-2/

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