I would like to point out something that not many people have thought through. While the intent of the morning after pill pricks the conscience of many, the effect is basically the same as that of the more common forms of the birth control pill. Both the morning after pill and the 'regular' contraceptive pill (and the patch, and the ring, and the shot for that matter) work in at least 4 ways. In some women, they suppress ovulation. They thicken the cervical mucous to block sperm transport. They partially paralyze the cilia of the fallopian tubes so that both sperm transport up and egg transport down are impeded. And they render the lining of the uterus thin and inhospitable, so that the conceptus can not snuggle in and grow.
There is one other possible effect that I have not seen examined in the literature, but that occurs to me based on my own studies of hormone chemistry. The synthetic progestins that are contained in all hormonally based contraceptives may also block natural progesterone, causing a pregnancy to fail even after implantation. I don't know if this happens, I don't know how one could even begin to find out. But I think it may also be a possible mechanism of action.
