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[Pharmacology](https://durgical.com/en/pharmacology/) · [Antiprogestogens (progesterone receptor modulators)](https://durgical.com/en/pharmacology/classes/antiprogestogens/)

# Mifepristone

Progesterone receptor blocker used with misoprostol to end an early intrauterine pregnancy or to empty the uterus after fetal death (WHO essential list).

Updated 2026-11-01

- Class: [Antiprogestogens (progesterone receptor modulators)](https://durgical.com/en/pharmacology/classes/antiprogestogens/)
- Receptor: Progesterone receptor (PGR); also glucocorticoid receptor
- ATC code: G03XB01
- WHO Model List of Essential Medicines

◎**Progesterone receptor (PGR); also glucocorticoid receptor**Mifepristone

ⓘ Crystal structure of the ligand-binding domain of the human progesterone receptor with mifepristone (RU486) bound.

**Target in 3D:** Progesterone receptor (PGR); also glucocorticoid receptor. PDB structure 2W8Y (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/2W8Y) · Drag to rotate · pinch to zoom

## Mechanism of action

Mifepristone is a steroid that binds the progesterone receptor without activating it. Without progesterone action the decidua breaks down, the cervix softens and the uterus contracts and becomes more sensitive to prostaglandins; misoprostol given afterwards completes the expulsion. It also blocks the glucocorticoid receptor and has weak antiandrogen activity.

- Mifepristone occupies the progesterone receptor and blocks it
- The decidua breaks down and the cervix softens
- The uterus becomes sensitive to prostaglandins
- Misoprostol, given afterwards, causes expulsion

## Pharmacokinetics

**Absorption**
By mouth; about 69% bioavailability

**Distribution**
About 98% bound to plasma proteins

**Metabolism**
Liver, mainly through CYP3A4

**Elimination**
Mostly in faeces

**Half-life**
About 18 hours (terminal)

## Indications

- Medical termination of an early intrauterine pregnancy, together with misoprostol
- Emptying of the uterus after fetal death, together with misoprostol (WHO essential list) [Miscarriage (early pregnancy loss) →](https://durgical.com/en/conditions/miscarriage/)

## Adverse effects

### Common

- Cramping and bleeding heavier than a period (expected)
- Nausea, vomiting and diarrhoea
- Fever or chills, weakness and headache
- Dizziness

### Serious (rare, important)

- Serious and rarely fatal infection and sepsis, which can occur without fever
- Prolonged heavy bleeding that may need surgical treatment
- Undiagnosed ectopic pregnancy that ruptures
- Allergic reactions

## Contraindications

- Confirmed or suspected ectopic pregnancy, or an undiagnosed adnexal mass
- Intrauterine device in place (it is removed first)
- Chronic adrenal failure or long-term corticosteroid therapy
- Bleeding disorders or anticoagulant therapy
- Inherited porphyria
- Allergy to mifepristone, misoprostol or other prostaglandins

## Key interactions

**CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, dexamethasone, St John's wort)**
Lower mifepristone levels and possible failure

**CYP3A4 inhibitors (ketoconazole, itraconazole, erythromycin, grapefruit juice)**
Higher mifepristone levels

**Narrow-margin CYP3A4 substrates**
Mifepristone can raise their levels for a long time

**Corticosteroids**
Their effect is blocked at the glucocorticoid receptor

## What is monitored

- Ultrasound or clinical assessment beforehand to confirm an intrauterine pregnancy and its duration
- Follow-up to confirm that the pregnancy has ended
- Amount and duration of bleeding; haemoglobin if heavy
- Signs of infection: fever, abdominal pain, fast pulse, even without fever
- Rh status, with the same prevention as after surgical abortion

## Administration and safety

- Given by mouth, followed later by misoprostol according to the protocol in use.
- Ectopic pregnancy is excluded and any IUD is removed before use.
- The patient receives clear written instructions on whom to call and when to go to an emergency service.

## Nursing care

- Before use: confirm pregnancy location and duration, Rh status, anticoagulants, steroids and adrenal disease.
- Teaching: cramping and bleeding are expected; soaking pads for hours, fainting, fever or severe pain need urgent care.
- Explain that infection can present without fever: weakness, abdominal pain or a fast heart rate also count.
- Arrange follow-up to confirm the outcome.

## Pregnancy and breastfeeding

Used only to end an early pregnancy or empty the uterus after fetal death; follow-up confirms the outcome, and an ongoing pregnancy is usually completed with a procedure.

## Memory aid

«Mife first, Miso second»: mifepristone primes the uterus (blocks progesterone), misoprostol pushes.

## Test yourself

Think of the answer, then tap the question to see it.

## Which diagnosis must be excluded before mifepristone is used?

Ectopic pregnancy: mifepristone does not treat it, and a rupture could be missed.

## Why is mifepristone contraindicated in chronic adrenal failure?

It also blocks the glucocorticoid receptor and could precipitate adrenal insufficiency.

## Which medicine follows mifepristone in the WHO-listed regimen?

Misoprostol, which causes the uterine contractions that complete the expulsion.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/mifepristone/)

## Related drugs

- [Misoprostol](https://durgical.com/en/pharmacology/misoprostol/)
- [Ulipristal](https://durgical.com/en/pharmacology/ulipristal/)

## Related conditions

- [Miscarriage (early pregnancy loss)](https://durgical.com/en/conditions/miscarriage/)

[← Back to the class: Antiprogestogens (progesterone receptor modulators)](https://durgical.com/en/pharmacology/classes/antiprogestogens/)

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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b63fad9b-7f12-4400-9019-b0586054e534) (DailyMed (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/medicines/242) (World Health Organization, 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=G03XB) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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