Pharmacology · Class
Antiprogestogens (progesterone receptor modulators) !
Steroids that block or modulate the progesterone receptor: mifepristone for medical abortion and ulipristal for emergency contraception.
Updated 2026-11-01
What they are
Medicines that bind the progesterone receptor and block or modulate the action of progesterone. Mifepristone, with misoprostol, ends an early pregnancy or empties the uterus after fetal death; ulipristal delays ovulation and is used as emergency contraception.
Mechanism of action
Progesterone keeps the endometrium (decidua) and a pregnancy in place and blocks contractions. Blocking its receptor breaks down the decidua, softens the cervix and makes the uterus sensitive to prostaglandins. Before ovulation, a receptor modulator delays the LH surge and so ovulation. Mifepristone also blocks the glucocorticoid receptor.
Target: Progesterone receptor (PGR)
Drugs in this class
- MifepristoneProgesterone receptor blocker used with misoprostol to end an early intrauterine pregnancy or to empty the uterus…Progesterone receptor (PGR); also glucocorticoid receptor
- UlipristalProgesterone receptor modulator taken once after unprotected sex to delay ovulation (emergency contraception, up to 5…Progesterone receptor (PGR)
Test yourself
Think of the answer, then tap the question to see it.
How does blocking the progesterone receptor end an early pregnancy?
The decidua breaks down, the cervix softens and the uterus becomes sensitive to prostaglandins and contracts.
Which second receptor does mifepristone block, and what contraindication follows?
The glucocorticoid receptor: it is contraindicated in chronic adrenal failure and long-term corticosteroid therapy.
How does ulipristal prevent pregnancy?
It delays or prevents ovulation; it does not end an existing pregnancy.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - MIFEPRISTONE tablet (DailyMed (U.S. National Library of Medicine), 2026); Ulipristal: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.