Pharmacology · Class
Selective oestrogen receptor modulators (SERMs) !
Drugs that act like oestrogen in some tissues and block it in others: they treat breast cancer, prevent bone loss or trigger ovulation.
Updated 2026-11-01
What they are
Ligands of the oestrogen receptor whose effect depends on the tissue. Tamoxifen blocks oestrogen in the breast and is used for breast cancer; raloxifene protects bone and lowers breast cancer risk; clomifene blocks oestrogen feedback in the hypothalamus and is used to induce ovulation.
Mechanism of action
All SERMs bind the oestrogen receptor. The shape the receptor takes with each drug decides which co-activators or co-repressors it recruits, and those differ between tissues. The result is an agonist in one organ and an antagonist in another: tamoxifen blocks the breast but stimulates the endometrium and bone, raloxifene stimulates bone but not the endometrium, and clomifene blocks the hypothalamus so that it releases more GnRH.
Target: Oestrogen receptor (ERα, gene ESR1)
Drugs in this class
- TamoxifenA breast cancer tablet that blocks oestrogen in the breast but acts like it in the uterus and bone. It raises the risk…Oestrogen receptor alpha (ERα)
- RaloxifeneA tablet for postmenopausal osteoporosis that acts like oestrogen on bone but not on the uterus. It also lowers breast…Oestrogen receptor alpha (ERα)
- ClomifeneA tablet that tricks the brain into sensing low oestrogen, so it releases more hormones that make the ovary ovulate…Oestrogen receptor alpha (ERα)
Test yourself
Think of the answer, then tap the question to see it.
How can one drug act as an oestrogen agonist in bone and an antagonist in breast?
The drug changes the receptor's shape, and each tissue has its own mix of co-activators and co-repressors, so the same receptor-drug complex switches genes on in one tissue and off in another.
Which serious adverse effect is shared by tamoxifen and raloxifene?
Venous thromboembolism: deep vein thrombosis and pulmonary embolism.
Why does tamoxifen raise the risk of endometrial cancer and raloxifene does not?
Tamoxifen acts as a partial oestrogen agonist on the endometrium, while raloxifene does not stimulate it.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Tamoxifen: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); DailyMed - RALOXIFENE HYDROCHLORIDE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2024).
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Representative model, for educational purposes only.