The morning-after pill is a type of emergency birth control (contraception). Emergency contraception is used to prevent pregnancy for women who've had unprotected sex or whose birth control method has failed.
The morning-after pill is intended for backup contraception only, not as a primary method of birth control. Morning-after pills contain either levonorgestrel (Plan B One-Step, Aftera, others) or ulipristal acetate (ella).
Levonorgestrel is available over-the-counter without a prescription; ulipristal acetate is available only with a prescription.
WHY IT'S DONE
Morning-after pills can help prevent pregnancy if you've had unprotected sex -- either because you didn't use birth control, you missed a birth control pill, you were sexually assaulted or your method of birth control failed.
Keep in mind that the morning-after pill isn't the same as mifepristone (Mifeprex), also known as RU-486 or the abortion pill. This drug terminates an established pregnancy -- one in which the fertilized egg has attached to the uterine wall and has begun to develop.
Emergency contraception is an effective option for preventing pregnancy after unprotected sex, but it isn't as effective as other methods of contraception and isn't recommended for routine use. Also, the morning-after pill can fail even with correct use, and it offers no protection against sexually transmitted infections.
The morning-after pill isn't appropriate for everyone. Don't take a morning-after pill if:
-- You're allergic to any component of the morning-after pill