Oestrogens
Also known as: estrogens, HRT oestrogen, oestrogen therapy, sex hormones
Steroid hormones that act on the oestrogen receptor. Estradiol and related oestrogens replace the ovaries' output after the menopause, treat genitourinary symptoms locally and feminise the body in gender-affirming care.
- Biological target
- Oestrogen receptor
- Also called
- estrogens, HRT oestrogen, oestrogen therapy, sex hormones
Mechanism of action
Oestrogens diffuse into cells and bind nuclear oestrogen receptors, which switch genes on or off. Estradiol, the ovaries' own hormone, is used for replacement; estriol is a weaker oestrogen in vaginal creams; conjugated oestrogens are an oral mixture; ethinylestradiol resists liver breakdown, which suits the combined pill but makes it more thrombogenic, so it is not used in HRT or feminising therapy. Oestrogen makes the endometrium proliferate, so anyone with a uterus takes a progestogen with systemic oestrogen. Oral routes raise clotting factors in the liver, unlike patches, gel and spray.
Members of the class
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Conditions treated
Class effects
- Breast tenderness, nausea, bloating, headache, leg cramps and fluid retention, especially in the first months
- Irregular bleeding in the first months of combined HRT; endometrial thickening if oestrogen is taken unopposed with a uterus
- Raised clotting factors and venous thromboembolism risk with oral routes, and a small rise in stroke risk with oral HRT
- Relief of hot flushes, improved vaginal and urinary symptoms, preserved bone density and, in feminising therapy, breast growth and fat redistribution
Cautions
- Previous or current breast cancer or other oestrogen-dependent cancer, undiagnosed vaginal bleeding, untreated endometrial hyperplasia, active or recent venous thromboembolism and active liver disease
- Systemic oestrogen without a progestogen when the uterus is present raises the risk of endometrial cancer
- A transdermal route is chosen where clot risk is raised: previous clots, obesity, smoking, migraine with aura, older age or immobility; oestrogen is usually paused around major surgery
- Combined HRT carries a small, duration-dependent increase in breast cancer risk that falls after stopping; breast awareness and screening continue
- Enzyme-inducing medicines reduce oestrogen levels, and oestrogens can increase levothyroxine requirements
Class warnings
- Oestrogens raise the risk of venous thromboembolism, most with oral preparations and least with transdermal ones; they are avoided in active or recent thromboembolism and a transdermal route is preferred where risk factors are present. UK
- Systemic oestrogen taken without a progestogen by anyone who has a uterus increases the risk of endometrial cancer; combined HRT carries a small increase in breast cancer risk related to duration of use. UK
Class interactions
| With | Effect | Source |
|---|---|---|
| Enzyme inducers (carbamazepine, phenytoin, rifampicin, St John's wort) | Increase oestrogen metabolism and lower its effect. | UK |
| Levothyroxine | Oestrogens raise thyroxine-binding globulin, so the levothyroxine dose may need to rise; TSH is checked. | UK |
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