Emergency Contraception Effectiveness: Facts and Myths

The effectiveness of emergency contraception depends on the time of administration. Levonorgestrel (Escapelle) is effective up to 72 hours, and ulipristal acetate (ellaOne) up to 120 hours after risky sexual contact. Both medications work by inhibiting ovulation, modifying cervical mucus, and affecting the uterine lining.

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What is the effectiveness of emergency contraception?

Emergency contraception is a method of preventing pregnancy that can be used after sexual intercourse. It is recommended in situations where a previously used contraceptive method has failed or sexual intercourse has taken place without protection. Examples of such situations include:

  • slipping, breaking, or incorrect application of a condom,
  • missing or delaying the intake of contraceptive pills,
  • situations preventing the absorption of oral contraceptive doses, such as vomiting,
  • detachment of the contraceptive patch,
  • failure to use any contraceptive method before or during intercourse,
  • in cases of sexual assault victims.

Pearl Index

The effectiveness of emergency contraception is determined by the Pearl Index, which is the ratio of the number of pregnancies to the number of women using a particular method per year. In the case of emergency contraception, the Pearl Index ranges from 1.5 to 2.5%. This means that out of 100 women using emergency contraception, 1.5-2.5 women may become pregnant within a year.

Mechanism of Action

Oral emergency contraception works by inhibiting or delaying ovulation. The released egg cell (oocyte) in this process can only be fertilized by a sperm for 24 hours, while sperm can survive in a woman’s reproductive tract for up to 5 days.


The effectiveness of emergency contraception depends on the time it is taken. The earlier it is taken, the more effectively it prevents pregnancy.

  • Tablets containing levonorgestrel are effective in 95% if taken within 24 hours of unprotected sexual intercourse. The effectiveness decreases to 85% if the tablets are taken within 72 hours.
  • Tablets containing ulipristal acetate are effective in 99% if taken within 24 hours of unprotected sexual intercourse. The effectiveness decreases to 85% if the tablets are taken within 72 hours.

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Side Effects

The most common side effects of emergency contraception include:

  • nausea and vomiting,
  • headache,
  • abdominal pain,
  • fatigue,
  • changes in the menstrual cycle.

Emergency contraception is an effective way to prevent pregnancy after unprotected sexual intercourse. However, it is essential to remember that it is a backup method and should not be used as a substitute for regular contraception.

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What Is the Effectiveness of Contraception? Clinical Studies

The effectiveness of the “morning-after pill” is influenced by various factors. These mainly include: the type of taken preparation, the phase of the menstrual cycle in which the preparation was taken, and the time that has passed since unprotected intercourse.

Effectiveness Depending on Time of Use After Intercourse

The therapeutic window for “morning-after pills” varies depending on the active substance. In the case of pills based on levonorgestrel (e.g., Escapelle), clinical studies conducted in 2010 showed that using the drug within 72 hours of unprotected intercourse prevents pregnancy in 97% of cases.

More modern preparations based on ulipristal acetate show effectiveness even up to 120 hours after intercourse. According to research and meta-analyses, they are characterized by even higher effectiveness reaching up to 99% and a pregnancy rate of 1.2%.

Effectiveness Depending on Type of Emergency Contraception

Emergency contraceptive pills, regardless of the active substance, have similar effectiveness if used according to the manufacturer’s recommendations. If embryo implantation in the uterine lining has already begun, the use of the “morning-after pill” will be ineffective.

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Common Mistakes and Factors Affecting the Effectiveness of Emergency Contraception

It is essential to emphasize that emergency contraception is not a preventive method, so it should not be used before engaging in intercourse. It is crucial to adhere to the time frames recommended by the drug manufacturer.

If the patient experiences vomiting or diarrhea within three hours of taking the “morning-after pill”, both for levonorgestrel-based and ulipristal acetate-based preparations, another dose of the drug should be taken immediately due to the possibility of reduced absorption.

Emergency contraception does not provide protection against sexually transmitted infections.

Effect of Time on Effectiveness

The most crucial criterion affecting the effectiveness of “morning-after pills” is the time of taking the preparation. Due to this, emergency contraception should only be taken in accordance with the manufacturer’s recommendations. With the passage of time from the start of treatment after unprotected intercourse, the risk of pregnancy development significantly increases. In the case of levonorgestrel-based preparations, their effectiveness decreases to approximately 16% if used later than 3 days.

Interactions with Other Medications

Both levonorgestrel and ulipristal acetate are metabolized by liver enzymes, mainly CYP3A4. Simultaneous use of other drugs that induce this enzyme may affect the pharmacokinetics of emergency contraception, reducing both its effectiveness and the effectiveness of other medicinal products used at the same time.

These include, among others: barbiturates, phenytoin, carbamazepine, herbal products containing St. John’s wort, rifampicin, ritonavir, rifabutin, griseofulvin. Additionally, simultaneous use of levonorgestrel and cyclosporine may increase the toxic effect of the antibiotic.

It is important to inform the doctor about all your illnesses, medications, and dietary supplements during the visit, especially herbal preparations, which often interact with medications.

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What are the side effects and contraindications of emergency contraception?

Emergency contraception is generally safe but may cause certain side effects, including:

  • nausea
  • vomiting
  • headache
  • irregular mid-cycle bleeding
  • fatigue
  • painful menstruation

Who should avoid its use?

Women should not use emergency contraception if they:

  • have uncontrolled severe bronchial asthma
  • have severe liver or kidney dysfunction
  • are pregnant (although there is no clinical data unequivocally indicating risk to the fetus)
  • have a risk of ectopic pregnancy (e.g., with tubal inflammation or a history of ectopic pregnancy)
effectiveness of emergency contraception

Effectiveness of the morning-after pill – frequently asked questions

Is emergency contraception 100% effective?

No, no method of contraception is 100% effective. The effectiveness of emergency contraception depends on the time of administration, the patient’s body weight, and other factors.

How long after intercourse can emergency contraception be used?

Emergency contraceptive pill should be taken as soon as possible, preferably within 72 hours (3 days) of intercourse. In the case of ulipristal acetate (ellaOne), this time is 120 hours (5 days).

Can emergency contraception be used as a regular method of contraception?

No, emergency contraception is not intended for regular use. It is designed for use in emergency situations, such as unprotected sexual intercourse or when another method of contraception has failed.

Is emergency contraception safe?

Generally, emergency contraception is safe. However, it may cause certain side effects such as nausea, vomiting, abdominal pain, headache, and menstrual bleeding.

Where can emergency contraception be obtained?

In Poland, emergency contraception is available only by prescription. A prescription can be issued by a doctor of any specialization, including primary health care physicians.

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Summary of Product Characteristics Escapelle, [online], [accessed 16.09.2023], available at: http://chpl.com.pl/data_files/2012-10-02_Escapelle_1500_ChPL_GedeonRichter.pdf

Summary of Product Characteristics ellaOne, [online], [accessed 16.09.2023], available at: https://ec.europa.eu/health/documents/community-register/2014/20141001129545/anx_129545_pl.pdf

Recommendations of the Polish Gynecological Society “Use of levonorgestrel in emergency contraception,” [online], [accessed 16.09.2023], available at: https://www.ptgin.pl/sites/scm/files/2021-09/02.2012%20-%20W%20TRAKCIE%20AKTUALIZACJI%20-%20Zastosowanie%20lewonorgestrelu%20%20w%20antykoncepcji%20awaryjnej.pdf

Clinical practice guidelines for obstetricians and gynecologists: Emergency contraception, ACOG Practice Bulletin, 2010, 05, 112.

World Health Organization website, [online], [accessed 16.09.2023], available at: https://www.who.int/en/news-room/fact-sheets/detail/emergency-contraception

Erecept.pl Portal, [online], [accessed 16.09.2023], available at: https://www.erecept.pl/tabletka-dzien-po-antykoncepcja-awaryjna

Redakcja recepta-online.info jest złożona z doświadczonych redaktorów i lekarzy specjalistów. Wiedzę zawartą w publikacjach opieramy o wieloletnie doświadczenie lekarzy POZ, ginekologów i neurologów, którzy biorą czynny udział w tworzeniu wiarygodnych treści popartych renomowanymi źródłami naukowymi. Dokładamy maksymalnych starań, aby nasze publikacje wyróżniały się szybkim dostępem do wiarygodnych informacji na temat recept online, antykoncepcji awaryjnej i innych tematów specjalistycznych.

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