How Effective Is the Morning-After Pill
The morning-after pill or emergency contraceptive pill is approximately 85% effective at preventing unplanned pregnancy

The morning-after pill, also called an emergency contraceptive pill (ECP), can be taken after unprotected intercourse to prevent an unplanned pregnancy. Emergency contraceptive pills are approximately 85% effective at preventing unplanned pregnancy. The sooner after sex you take the pill, the more effective it is.

Almost 95% of pregnancies can be avoided if the pill is taken within 24 hours. However, it can still prevent pregnancy if taken within 3-5 days of unprotected sex.

The morning-after pill is designed to be used in an emergency and should not be used as a replacement for regular contraceptives, such as condoms or intrauterine devices. If taken repeatedly, the pill can cause hormonal complications in the long run.

How does the morning-after pill work?

Conception takes place when sperm fertilizes an egg when it is released from an ovary during ovulation. However, since sperm can remain active in the female reproductive tract for up to 5 days, even if a woman is not ovulating during sex, she could still get pregnant if she ovulates within 5 days of unprotected sex.

Emergency birth control pills typically work by preventing or delaying the process of ovulation. There are two types of emergency birth control pills:

  • Ulipristal acetate (antiprogestin emergency contraception)
    • Available by prescription
    • Most effective form of birth control pill
    • Works best if taken within 5 days of unprotected sex
    • Works by altering the role of progesterone hormone, halting or delaying ovulation
  • Levonorgestrel (progestin emergency contraception)
    • Available over-the-counter (without a prescription)
    • Works best if taken within 3 days of unprotected sex
    • Works by delaying egg release from the ovary, preventing the sperm from fertilizing it

What can cause the morning-after pill to fail?

It is estimated that about 1 or 2 in every 100 women may get pregnant despite taking the morning-after pill within 72 hours of unprotected sex.

Factors that may lead to emergency contraceptive pill failure include:

Does the morning-after pill cause side effects?

There are no known serious risks associated with the use of emergency contraceptive pills.

However, taking the pill may cause your next period to come earlier or later. If your period is more than 7 days late or lighter than usual, take a pregnancy test as soon as possible.

Other potential side effects include:

How do you know if the morning-after pill has worked?

The only way to know the morning-after pill has worked is if your next period comes. 

Also, while emergency birth control provides a safe option to reduce the risk of pregnancy, it does not offer protection from sexually transmitted diseases.

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Medically Reviewed on 1/25/2022
References
Image Source: iStock Images

Stuart A. Levonorgestrel Emergency Contraception. WebMD. https://www.webmd.com/sex/birth-control/plan-b

World Health Organization. Emergency Contraception. https://www.who.int/news-room/fact-sheets/detail/emergency-contraception

Family Planning Victoria. Emergency Contraceptive Pill. https://www.fpv.org.au/for-you/contraception/emergency-contraception/morning-after-pill-emergency-contraception

KidsHealth. Emergency Contraception https://kidshealth.org/en/teens/contraception-emergency.html