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I am 100% pro-life but I have some questions if Plan B actally makes the uterine lining thin and inhospitable. Regular hormonal contraception will do that over time, after some months of use.

But there is a natural rise in progesterone after ovulation occurs which encourages the growth of the lining, and if conception has occured, the hormonal signals from the embryo tell the mother's body to keep producing progesterone and nourishing the lining.

I don't quite see the mechanism whereby a one-time dose of progestin (not the quite the same as natural progesterone, it is true) will impair the receptivity of the lining, as opposed to a several months' regime of progestin taken at times when the body isn't supposed to be producing much progesterone at all.

Any Freeper with a medical background here?

Mrs VS

The makers admit that Plan B stops implantation
from the makers website:
How does Plan B work (mechanism of action)?
Plan B is believed to act as an emergency contraceptive principally by preventing ovulation or fertilization (by altering tubal transport of sperm and/or ova). In addition, it may inhibit implantation by altering the endometrium. Plan B is not effective if a woman is pregnant. Plan B is a contraceptive and cannot terminate an established pregnancy.

The

Yes it does, which is why it is considered back-up contraception. The JP insititue for life and family has documentation proving this as does Human Life International and all other right to life organizations. This is why they opposed it.

It is also why Catholic hospitals were forbidden to prescribe it to rape victims, if they were unable to determine if the vicim had ovulated or not.

As an ex-pharmaceutical rep who worked for Searle and Schering Plough, here's my take on this pill. The Plan B effect creates a huge spike in the hormone which initiates the uterine lining build up ... this hormone is a trace chemical produced when the follicle has erupted and expelled an ovum, thus the spike is designed to prevent the release of the voum. Hormone cycle feedback is a delicate one and the huge spike results in an eventual inhospitable uterine lining rather than a gradually built up one, thus a menses results shortly rather than two weeks later.

The emergency contraception pill should not be confused with mifepristone (also called Mifeprex, and formerly known as RU-486), an abortifacient which is taken after implantation has occurred, aborting the pregnancy. The morning-after pill must be taken before implantation, or it will have no effect. Earlier, it was believed that emergency contraception worked by preventing blastocysts from implanting in the womb. Today, however, current medical science, as reflected in research papers published in respected medical journals, states that emergency contraception works by preventing ovulation. Recent medical studies in animals (the rat and the monkey) did not suggest that emergency contraception prevents implantation; however, this mechanism of action cannot be ruled out in all cases, as it is impossible to prove a negative.

My personal impression is that with studies indicating that such treatment is 89% effective at preventing pregnancy, that something more than preventing ovulation is going on. As for a specific mechanism of action that would prevent implantation, I can't really give you an answer to that.