Plan B known as Emergency contraceptive pills or morning-after pill. There are 2 kinds of Plan B in the market two step therapies and one step therapy. Both kind of Plan B are available over the counter and sold under the supervision of pharmacist. Women under 17 need a prescription.  Plan B works in two ways (stop ovulation and changing in cervical mucus and uterine lining) to preventing pregnancy after unprotected sex. Do not use Plan B if you are already pregnant. The Plan B should be taken as soon as possible, within 72 hours of unprotected sex. Plan B will not terminate a pregnancy that has already begun. Plan B is not RU-486 (the abortion pill).