A morning-after pill is a type of emergency female contraception. A woman can take this within 120 hours, or 5 days, of sexual intercourse without contraception that might lead to an unwanted pregnancy.

According to data from the 2006-2010 National Survey of Family Growth carried out by the Centers for Disease Control and Prevention (CDC), 11 percent of women in the United States have used emergency contraception. Of this figure, 59 percent have used it on one occasion.

In this article, we explore the different types of morning-after pill, how to choose, and the possible side effects.

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A morning-after pill can prevent an unwanted pregnancy.

The morning-after pill is a medication that a woman can take 3–5 days after having sexual intercourse without contraception to prevent a pregnancy.

People may require emergency contraception after sex for many reasons, including:

  • forgetting to use a primary method of birth control
  • condom breakage or slippage
  • failing to use the withdrawal method effectively
  • having unplanned or unintended sexual intercourse without contraception
  • sexual assault or rape

There are different forms of the morning-after pill that contain the hormones levonorgestrel or ulipristal acetate.

The morning-after pill works primarily by preventing ovulation, which is when the ovary releases an egg, blocks fertilization of an egg, and stops a fertilized egg from implanting in the wall of the uterus. According to the Mayo Clinic, fertilization can occur up to 5 days after having intercourse.

According to the World Health Organization (WHO), between 1.2 and 2.1 percent of women who took the morning-after pill containing levonorgestrel became pregnant, compared to 1.2 percent of women who took tablets containing ulipristal acetate.

The WHO adds that people must take these pills as soon as possible after sex without contraception — ideally, within 72 hours, or 3 days. While some of the pills may still work up to 120 hours, or 5 days, after intercourse without contraception, they become less effective.

A range of brands contain levonorgestrel, including Plan B One-Step. Only one brand of morning-after pill called ella contains ulipristal acetate. Always read the prescribing information on the packages, as advice on how and when to take the medications varies between brands.

The morning-after pill does not disrupt an established pregnancy so will not result in a pregnancy loss, or abortion. Also, it will not protect against pregnancy if a person has sex without contraception shortly after taking the pill. Anyone intending to have sexual intercourse should start or continue with regular methods of contraception.

Choosing the right morning-after pill can increase the chances of successfully preventing a pregnancy

Some earlier literature suggested that emergency contraceptive pills that contain levonorgestrel may be less effective in women with a high body mass index (BMI). A study published in 2017 in the journal Contraception notes that some people with obesity and a BMI of over 30 may experience reduced efficacy from this type of morning-after pill.

However, it also states that healthcare professionals should still offer medicines containing levonorgestrel to all women that need them, regardless of weight or BMI. The study also recommends additional counseling and guidance for those who have obesity.

According to Planned Parenthood, however, women with higher BMIs may find ella a more effective option. Those with extremely high BMIs might consider a copper IUD as emergency contraception.

Plan B One-Step and other pills that contain levonorgestrel are available over the counter, but some brands require a prescription for women who are 16 years of age or younger.

Women looking to take ella will require a prescription in all circumstances.

Morning-after pills range in price, costing from $15 to $50 for levonorgestrel to between $30 to $65 for ella.

Depending on the brand, a woman can sometimes use different doses of her regular birth control pill as emergency contraception under the direction of a healthcare professional.

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Headaches might be a side effect of taking emergency contraception.

While the morning-after pill offers women a safe option to prevent pregnancy, it does have some disadvantages. These include mild side effects and no protection against sexually transmitted diseases.

Temporary side effects of a morning-after pill include:

  • menstrual changes
  • breast tenderness
  • dizziness
  • headaches
  • cramping
  • nausea
  • vomiting

The morning-after pill loses efficacy if vomiting occurs within 3 hours of consumption. Anyone who vomits after taking the morning-after pill should take an additional dose.

Frequent use of the morning-after pill can cause menstrual irregularities, such as irregular and unpredictable periods. If the menstrual cycle does not resume within 3-4 weeks of using the morning-after pill, take a pregnancy test.

Other methods of contraception are available for regular or on-going birth control.

While the morning-after pill is generally safe, some women should not take it, including:

  • women who have an allergy or sensitivity to the ingredients
  • women who are pregnant

Doctors do not recommend that women who are pregnant or breastfeeding take ulipristal acetate, as scientists do not know the risks to the fetus or infant.

According to some prescribing information from the Food and Drugs Administration (FDA), some pregnant animals experienced adverse effects after taking ulipristal acetate during the first trimester of pregnancy.

Levonorgestrel is not harmful during pregnancy, although a woman should not take it if she knows she is pregnant. Women who are breastfeeding can take levonorgestrel since there are no known adverse effects to an infant.

Anyone who notices bleeding or spotting that lasts longer than a week, or experiences severe lower abdominal or pelvic pain should contact a healthcare provider as these symptoms could indicate an ectopic pregnancy or miscarriage.

Another option for emergency contraception is a copper IUD, also known as ParaGard (copper) IUD. This involves a medical professional inserting the device into the uterus to prevent pregnancy.

According to Planned Parenthood, the device is 99.9 percent effective when a medical professional applies it within 5 days, 120 hours, of having sex without contraception.

The additional benefit of ParaGard is that, in addition to acting as emergency contraception, it also provides effective birth control for up to 10 years.

Anyone considering emergency contraception should speak with a healthcare professional about suitable options.