Emergency contraception is nothing more than a higher dose of the same active ingredients in already approved birth control pills, taken within 72 hours of unprotected intercourse to prevent pregnancy. They may also reduce the likelihood of implantation of the ovum in the uterus. The timing in the menstrual cycle when emergency contraception is taken, and the time that it is taken after unprotected intercourse, may be important factors in determining the mode of action and effectiveness for each woman in any given situation. Emergency contraception is considered to be more effective if it is taken soon after unprotected intercourse.
Emergency contraception has no effect after the ovum is implanted in the uterus.
Because emergency contraception has no effect on such an established pregnancy, it is not considered an abortifacient. Emergency contraception could significantly reduce the number of unwanted pregnancies and abortions worldwide. The Yuzpe regimen was developed by Canadian physician A. A. Yuzpe in the early 1970s. Under the protocol Yuzpe developed, which was published in the Federal Register in 1997, women take two birth control pills of the brand Ovral within 72 hours of unprotected intercourse and repeat the treatment 12 hours later. If Ovral brand pills are not available, women can use any one of six other brands that contain exactly the same ingredients.