How Long Is the Morning After Pill Effective For?


The "morning after pill," or emergency contraception, is a pill that contains synthetic hormones that will prevent pregnancy if taken properly after unprotected or compromised sexual intercourse. Available over-the-counter since 2006, emergency contraceptives are an effective way to prevent unintended pregnancy, and are most effective when taken as quickly as possible.

Preventing Ovulation

When the “morning after pill” hit the over-the-counter market in 2006, the public could obtain emergency contraceptives for the first time ever without a prescription . The emergency contraception pill was regarded as a viable solution to failed condom use or the occasional lapse in judgment that led to unprotected sex. Several years later, the morning-after pill continues to be popular because of its reliability and ease of use.

This pill, which has an 80 to 90 percent effectiveness rate when taken within 72 hours of unprotected or compromised sexual intercourse, works by utilizing a large dose of the synthetic hormone levonorgestrel to prevent ovulation. Without the occurrence of ovulation, an egg is not released from a patient's ovary, and fertilization of the egg cannot occur.

Preventing Implantation

The hormones in emergency contraception also prevent the uterus from building up the nutrient-rich lining that is required for a blastocyst, or early-fertilized egg, from attaching to the uterine wall and growing into an embryo. In this instance, if a woman who has already ovulated and conception occurs before or shortly after taking the emergency contraception, the embryo would not be able to attach to the wall of her uterus and would likely be expelled during her regular menstrual period. She wouldn't know this ever happened, as the size of the fertilized egg at this point would be nearly microscopic.


The morning-after pill, including the popular U.S. Brand “Plan B," must be taken within 72 hours of unprotected sex. While some brands of emergency contraception can be taken up to 120 hours after unprotected intercourse, medical experts agree that due to the decrease in effectiveness in the morning-after pill after three days, the 72-hour marker is an important one for women looking for a reliable method to prevent pregnancy on an emergency-only basis.

The very name “morning after” pill is a good indicator that emergency contraception works best when taken the morning after unprotected sex. While patients can wait up to three days to take the pill, it has its highest effectiveness rate when taken within 24 hours of the incident.


The morning-after pill is not effective in terminating an existing pregnancy. Once the fertilized egg has attached to a patient's uterine wall, an abortion must occur if the woman wishes not to be pregnant. Since this implantation of the embryo occurs within approximately three to five days of unprotected sex, the cut-off time for the morning after pill correlates. For emergency contraception to be effective, err on the side of caution and take them within 72 hours of unprotected sex; otherwise, implantation can occur and pregnancy begin.

After Implantation

If despite her efforts to prevent pregnancy a woman becomes pregnant, a medication abortion can be the next best method of termination. The medication abortion, also known as the abortion pill, induces miscarriage in early pregnancy.

To obtain information on medication abortion, contact your local family planning center or women's health clinic.

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