Oral oestrogen passes through the liver first and raises clotting factors; transdermal oestradiol, by patch or gel, largely avoids this and has been associated with lower venous thromboembolism risk in observational studies. For a woman with raised clot risk — obesity, a past provoked clot, or migraine with aura where hormone therapy is still being considered — transdermal is the usual choice when hormone therapy is appropriate.
A woman with a uterus needs a progestogen as well, whatever the oestrogen route, to protect the endometrium.
- Prefer transdermal oestradiol in women with higher venous thromboembolism risk, such as obesity.
- Add a progestogen for any woman with a uterus, whether oestrogen is oral or transdermal.
- Ask about previous clots, migraine with aura and breast cancer before starting any hormone therapy.
- Review symptom benefit and the ongoing need for therapy at least once a year.
Why it matters
The route, not just the decision to treat, changes the clot risk a woman accepts.
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