The "morning after pill"
With this method high dosages of estrogen combined with progesterone or a high dosage of pure progesterone is ingested as soon as possible after unprotected sexual intercourse or within 72 hours afterwards, at the latest. The efficiency of this approach amounts to around 99%, but it represents a hormonal overdose.
Various mechanisms appear to work together: namely an inhibition of ovulation, interference with the transport of the oocyte/sperm through the fallopian tube, interference with fertilization, and changes to the endometrium. Thereby this contraceptive method intervenes before the oocyte is implanted in the uterus.
Is a chemical substance that interrupts early pregnancy. The active substance is a synthetic steroid molecule, the strongly anti-progesterone-property of which is based on a competitive inhibition of the progesterone receptors. Mifepriston or RU486, which gives the pill its name, has an anti-nidation effect on the endometrium, the uterine muscle, and the cervix.
With this type of pregnancy interruption, the efficiency is increased to 95% by a combination with prostaglandins. The rejection of the embryo is also accelerated. Mifeprison must be ingested, though, within 49 days, at the latest, after menstrual bleeding has ceased.