some website Wrote:
Birth control pills fool the body into acting as if it's pregnant. Birth control pills, also called oral contraceptives (OCs), come in two forms: the combined OC, a combination of two synthetic hormones, estrogen and progestin; and, the minipill, which consists solely of progestin. Combined OCs are more commonly used, though both kinds are available through health care providers. The combination pill prevents ovulation by suppressing the natural hormones in the body that would stimulate the ovary to release an egg. By taking this estrogen throughout the month, you insure that no egg will be developed or released for that cycle. Progestin thickens the cervical mucus, hindering the movement of sperm. Progestin also prevents the uterus's lining from developing normally; so, if an egg were fertilized, implantation is unlikely.
The minipills, which contain no estrogen, inhibit the egg's ability to travel through the fallopian tubes, alter the cervical mucus to block sperm, partially suppress the sperm's ability to unite with an egg, and partially inhibit implantation in the uterine wall. For maximum effectiveness, you need to take the pills as prescribed.
I'll bet if you took enough of the first kind, you'd notice some... em... changes.