Mode of action
Lena Marions MD PhD,
Dep of Ob/Gyn, Karolinska University Hospital Stockholm Sweden
Emergency contraception is a method that is used after sexual intercourse to prevent unwanted pregnancy. Available methods are combined contraceptive pills (the Yuzpe method), levonorgestrel only, the antiprogesteron mifepristone and the insertion of a copper IUD.
Levonorgestrel has become the drug of choice in many countries because it is effective and well tolerated. However due to lack of knowledge, about the mechanism of action, millions of women have no access to postcoital contraception because of religious and/or political reasons. The sensitive question is whether the mode of action is exerted before or after fertilization. The only method that has shown to exert an inhibitory effect on the implantation process is the copper IUD, the EC pills act by postponing or prevention of ovulation and can not be regarded upon as abortifacient.
Even though the use of EC pills has significantly increased during the last years, the number of induced abortions has not decreased as expected. Studies indicate however that both women and providers have a tendency to underestimate the risk for pregnancy. It is important to recommend treatment after every unprotected intercourse at any time during the menstrual cycle.