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.
The last sentence gives it away...
It's bad science to use the package insert disclaimer and ignore all sorts of new evidence that the Plan B protocol only works to block ovulation and therefore will only work for 5 days before ovulation (the most fertile period in a natural cycle, anyway) and may actually increase the implantation of any embryo after fertilization (if the embryo is in the uterus when the hormone effects are present). Croxatto and Durand have documented the lack of change in the uterine wall with the progesterone-only protocols.
The most significant are the studies from Brazil
by Croxatto and his group (H.B. Croxatto et al. / Contraception 70
(2004) 442–450)," which was a blind study, cycling women who were
otherwise unable to get pregnant (sterilized or with - what I consider
unethical and potentially abortifacient - IUD's) through 3 courses -
placebo, and two forms of progesterone-only pills. The researchers
followed the women with serial ultrasound and hormonal blood essays.
There is a study by Durand, et.al. (M. Durand et al. / Contraception 71
(2005) 451– 457), from 2001 which tested surgically sterilized women
given 2 doses of Levonorgestrel, 12 hours apart. These women were
studied by serial ultrasounds and women who ovulated also underwent
endometrial biopsy. There was no difference in their uterine lining
function or anatomy although there was a difference in the expression of
glycodelin-A. This protein prevents binding of the sperm to the zona
pellucida of the oocyte and so, prevents fertilization. (There is some
speculation that the protein acts to help implantation, too.)
I do not believe that hormone preparations should be "OTC" or dispensed without a physician's prescription, however. A woman with unprotected sex is likely to have more problems than a risk of "unwanted pregnancy."
The pill does not work to acheive the public health goal of fewer pregnancies and/or cutting intentional interventional abortions.
Now, before I get flamed I've never been on one of these threads so I'm not "jumping" on any band wagon. I know it's a slippery slope but I'm wondering everyone's take on it if used right away.
It "may" do that, there's just a complete absence of any evidence. All the evidence suggests that the hormones -- the same hormones that are in "the Pill" prevent fertilization, not implantation. This is not an abortion drug.