Pharmacology · Hormonal contraceptives
Levonorgestrel !
Progestin used alone as emergency contraception (within 3 days), in progestin-only pills, implants and intrauterine systems. No estrogen.
Updated 2026-11-01
Crystal structure of the ligand-binding domain of the human progesterone receptor with levonorgestrel bound.
Mechanism of action
Levonorgestrel is a synthetic progestin that activates the progesterone receptor. As emergency contraception it mainly prevents or delays ovulation; in daily or long-acting forms it also thickens cervical mucus and thins the endometrium. It does not work once a pregnancy is established and does not harm it.
- Levonorgestrel activates the progesterone receptor
- Ovulation is prevented or delayed
- Cervical mucus thickens; an established pregnancy is not affected
Pharmacokinetics
- Absorption
- Almost complete by mouth, without first-pass metabolism
- Metabolism
- Reduction, hydroxylation and conjugation; enzyme inducers lower its levels
- Half-life
- About 34 hours (measured with the combined pill)
Indications
- Emergency contraception after unprotected sex or contraceptive failure, as soon as possible and within 3 days
- Progestin-only contraception (pill, implant, intrauterine system)
Adverse effects
Common
- Changes in the next period (earlier, later, heavier or lighter)
- Nausea, vomiting and lower abdominal pain
- Tiredness, headache and dizziness
- Breast tenderness
Contraindications
- Known allergy to levonorgestrel
- Not used in a known pregnancy: it does not work then
Key interactions
- Efavirenz, rifampicin and some antiepileptics
- Lower levels and less effect
- St John's wort and other enzyme inducers
- Less contraceptive effect
What is monitored
- Timing of the next period; pregnancy test if it is more than a week late
- Severe abdominal pain (ectopic pregnancy)
Administration and safety
- Emergency use: one oral dose as soon as possible after unprotected sex, within 3 days; the earlier, the better it works.
- If vomiting occurs within 2 hours, the patient contacts the health service about another dose.
- It is a backup method, not for regular contraception.
Nursing care
- Ask the timing of unprotected sex and the last period, and current medicines (enzyme inducers).
- 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.
- Severe abdominal pain needs urgent review for ectopic pregnancy.
- Offer information on regular contraceptive methods.
Pregnancy and breastfeeding
It does not end or harm an established pregnancy; it is not used when pregnancy is known.
Test yourself
Think of the answer, then tap the question to see it.
What is the main mechanism of levonorgestrel as emergency contraception?
It prevents or delays ovulation; it does not end an established pregnancy.
Within how many days after unprotected sex is levonorgestrel used, compared with ulipristal?
Levonorgestrel within 3 days; ulipristal up to 5 days. Both work better the sooner they are taken.
Which HIV medicine lowers the effect of levonorgestrel?
Efavirenz, an enzyme inducer.
Related drugs
← Back to the class: Hormonal contraceptives
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 - LEVONORGESTREL TABLET, 1.5 MG tablet (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - LEVONORGESTREL AND ETHINYL ESTRADIOL kit (DailyMed (U.S. National Library of Medicine), 2026); 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.