Mechanism of action of emergency contraception

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. (C) 2010 Elsevier Inc. All rights reserved.