Small molecule
PubChem CID 13109
Levonorgestrel
Plan B One-Step
- Mechanism of action
- Synthetic progestin — progesterone receptor agonist
- In plain language
- Temporarily delays the release of an egg from the ovary, so there's no egg around for sperm to fertilize.
- How it works
- Levonorgestrel is a synthetic progestin with high-affinity agonist activity at the progesterone receptor. Administered before the luteinizing hormone (LH) surge, it suppresses that surge and inhibits or delays follicular rupture, postponing ovulation by several days — long enough for any sperm present to lose viability before an egg is released. Current FDA-reviewed evidence indicates the drug does not have a demonstrated direct effect on fertilization or on the endometrium, and it does not interrupt an established pregnancy. Because its effect depends on acting prior to the LH surge, efficacy declines sharply once ovulation has already occurred.
- Therapeutic applications
- Indicated for the prevention of pregnancy following unprotected intercourse or a known or suspected contraceptive failure. Not indicated for routine contraceptive use, and not effective for termination of an established pregnancy.
- Class
- Small molecule
- Therapeutic area
- Reproductive health / Contraception
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