Pharmacology · Antiprogestogens (progesterone receptor modulators)
Ulipristal !
Progesterone receptor modulator taken once after unprotected sex to delay ovulation (emergency contraception, up to 5 days). It does not end a pregnancy.
Updated 2026-11-01
Also called: Ulipristal acetate
Crystal structure of the human progesterone receptor with ulipristal acetate and a co-repressor peptide.
Mechanism of action
Ulipristal is a selective progesterone receptor modulator. Taken before ovulation, it delays or prevents the release of the egg, so sperm already present cannot fertilise it. It may also change the endometrium. It does not affect an established pregnancy.
- Ulipristal binds the progesterone receptor and modulates it
- Ovulation is delayed or prevented
- Without an egg, fertilisation does not happen
Pharmacokinetics
- Absorption
- Single tablet by mouth
- Metabolism
- Liver, through CYP3A4
Indications
- Emergency contraception up to 5 days after unprotected sex or contraceptive failure
Adverse effects
Common
- Painful periods, spotting or a change in the next period
- Nausea
- Tiredness, headache and dizziness
Contraindications
- Known pregnancy (it is not used to end one)
- Hypersensitivity to ulipristal
Key interactions
- Hormonal contraceptives started within 5 days
- Both may work less well; a barrier method is used until the next period
- CYP3A4 inducers such as St John's wort
- Lower ulipristal levels and less effect
What is monitored
- Timing of the next period; a pregnancy test if it is more than a week late
- Severe abdominal pain (ectopic pregnancy)
Administration and safety
- One tablet, as soon as possible after unprotected sex, within 5 days.
- If vomiting occurs within 3 hours, the patient contacts the health service about another dose.
- Not for regular contraception and not more than once per cycle.
Nursing care
- Ask the date of unprotected sex and of the last period, and whether hormonal contraception is used.
- Teaching: wait at least 5 days before starting or resuming hormonal contraception, and use a barrier method until the next period.
- Teaching: it does not protect against HIV or other sexually transmitted infections.
- Advise a pregnancy test if the period is more than a week late, and urgent care for severe abdominal pain.
Pregnancy and breastfeeding
It is not used to end a pregnancy; if pregnancy is suspected, it is confirmed before use.
Test yourself
Think of the answer, then tap the question to see it.
Up to how many days after unprotected sex can ulipristal be used?
Up to 5 days (120 hours), as early as possible.
Why should hormonal contraception not be started within 5 days of ulipristal?
Taking hormonal contraception within 5 days of ulipristal may make both less effective; a barrier method is used until the next period.
How does ulipristal prevent pregnancy?
It delays or prevents ovulation; it does not end an established pregnancy.
Related drugs
← Back to the class: Antiprogestogens (progesterone receptor modulators)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Ulipristal: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); eEML - Electronic Essential Medicines List (World Health Organization, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.