How do levonorgestrel-only emergency contraceptive pills prevent pregnancy? Some considerations

Gynecol Endocrinol. 2011 Jun;27(6):439-42. doi: 10.3109/09513590.2010.501885. Epub 2010 Jul 29.


Controversial opinions exist about the possible mechanisms throughout emergency contraception prevents pregnancy. Recently, the International Federation of Gynaecology and Obstetrics and the International Consortium for Emergency Contraception released a Joint Statement declaring that 'inhibition or delay of ovulation should be their primary and possibly only mechanism of action'. They still added that 'Review of the evidence suggests that LNG-ECPs cannot prevent implantation'. Concerning levonorgestrel-only emergency contraceptive pills effects on ovulation, the Statement based on seven reference papers which considered a total of only 142 patients, divided into still different subgroups. Basing on their same references we got quite different conclusions.

Publication types

  • Evaluation Study
  • Review

MeSH terms

  • Contraception, Postcoital / methods*
  • Contraceptive Agents, Female / administration & dosage
  • Contraceptive Agents, Female / pharmacology
  • Contraceptives, Postcoital / administration & dosage
  • Contraceptives, Postcoital / pharmacology
  • Embryo Implantation / drug effects
  • Female
  • Humans
  • Levonorgestrel / administration & dosage*
  • Levonorgestrel / pharmacology*
  • Ovulation / drug effects
  • Pregnancy / drug effects*
  • Signal Transduction / drug effects
  • Tablets


  • Contraceptive Agents, Female
  • Contraceptives, Postcoital
  • Tablets
  • Levonorgestrel