Mechanism of action of emergency contraception

Contraception. 2010 Nov;82(5):404-9. doi: 10.1016/j.contraception.2010.05.004.


A major barrier to the widespread acceptability and use of emergency contraception (EC) are concerns regarding the mechanisms of action of EC methods. Today, levonorgestrel (LNG) in a single dose of 1.5 mg taken within 120 h of an unprotected intercourse is the most widely used EC method worldwide. It has been demonstrated that LNG-EC acts through an effect on follicular development to delay or inhibit ovulation but has no effect once luteinizing hormone has started to increase. Thereafter, LNG-EC cannot prevent ovulation and it does not prevent fertilization or affect the human fallopian tube. LNG-EC has no effect on endometrial development or function. In an in vitro model, it was demonstrated that LNG did not interfere with blastocyst function or implantation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Adolescent
  • Adult
  • Animals
  • Contraception, Postcoital / methods
  • Contraceptives, Postcoital / pharmacology*
  • Female
  • Genitalia, Female / drug effects
  • Humans
  • Levonorgestrel / pharmacology
  • Male
  • Norpregnadienes / pharmacology
  • Ovarian Follicle / drug effects*
  • Ovulation / drug effects*
  • Receptors, Progesterone / agonists
  • Receptors, Progesterone / antagonists & inhibitors
  • Reproduction / drug effects
  • Young Adult


  • Contraceptives, Postcoital
  • Norpregnadienes
  • Receptors, Progesterone
  • Levonorgestrel
  • ulipristal acetate