The pill works in one of two ways.

As a contraceptive, it can either prevent ovulation or thicken the mucous in a woman's reproductive tract (cervix, uterus, fallopian tubes) making it harder for sperm to reach the egg in a woman's fallopian tube, thereby preventing fertilization (starting of new human life).

As an abortifacient, it irritates the lining of the uterus, making it harder for the embryo to attach to the uterus. If a woman has already ovulated and a sperm does manage to fertilize the egg, then Plan B works by preventing this new human life from implanting (starting on day six after fertilization) in the uterus causing death of an embryo.

Plan B does not end an already existing pregnancy once the embryo has been implanted in the uterus, and it does not protect against STD's.

Since the manufacturer says that Plan B can work by preventing implantation of an embryo, they appear to rely on recent re-definitions of conception, pregnancy and abortion.

According to the new definitions of some pro-choice groups, conception and pregnancy begin at implantation rather than at fertilization and abortion is the termination of a post-impantation pregnancy.

The drug makers can then claim that their statements are true under these new definitions, however, according to scientific fact, human life begins at fertilization with the first cell division.

Another confusing statement is that Plan B "does not harm the fetus." This is true as the fetal stage does not begin until eight weeks after fertilization and there is no evidence that the pill harms a human being after it has implanted in the uterus, which occurs during the second week.