Mechanism of action of the emergency contraceptive pill

The article was consulted professionally by Specialist I Pham Thi Yen – Obstetrician and Gynecologist – Share99 Hai Phong International Health Hub.

Emergency contraceptive pills can help if you have just had forgotten sex or improperly used protective measures. By using emergency contraception within 3 days of sexual contact (the earlier, the better), you can significantly reduce the likelihood of pregnancy.

1. Mechanism of Action

An emergency contraceptive pill is a method of using hormones or drugs that prevent pregnancy. Most of these hormones are similar to those in regular contraceptives. The drug works mainly by delaying the launch of eggs or ovulation. Once the egg has been transplanted, emergency contraception is no longer effective. If you are already pregnant, these pills will not work as a contraceptive.

Emergency contraception works well. But you should take it quickly – it is best to within 24 hours of sex. But the sooner you actually take it, the more effective it will be. If you perform emergency contraception within 72 hours of sex, the likelihood of pregnancy is only 1% to 2%.

Contraceptive pills

Women should not abuse emergency contraceptive pills

2. Types of emergency contraception

There are 3 types of emergency contraceptives in the form of tablets that are sold even when prescribed and without a prescription. Depending on the brand and dosage, you can take 1 tablet or 2 tablets.

  1. The drug contains a hormone called levonorgestrel: You should use these drugs within 72 hours after sex. But the drug still works up to 5 days later, but is less effective with the initial time.
  2. Contraceptive pills contain progesterone and estrogen. If you take them at a higher dose within 3 to 5 days of sexual contact, they will act as an emergency contraceptive. This approach is effective, but less effective than other forms of emergency contraception. Side effects, such as nausea, can also be worse. It is not recommended to use this method regularly unless prescribed by a doctor.
  1. Ulipristal (ella, ellaOne) is an emergency contraceptive drug that is sold only on prescription. This is an emergency form of contraception that does not use hormones but instead, it is a drug called ulipristal acetate, which blocks the action of hormones. The drug is effective up to 5 days after sex. If you think, you may be pregnant then ask for advice from your doctor before using it, as you should not take this drug during pregnancy.

Copper contraceptive ring (DCTC). This is a different approach. Medical staff will place a small plastic and copper contraceptive ring in the uterus to prevent sperm from fertilizing with eggs, avoiding pregnancy. The copper contraceptive ring is considered an effective form of emergency contraception and it is suitable for women who want long-term contraception.

T-shaped contraceptive ring

Copper contraceptive ring

The advantage of the contraceptive ring is that women can use it as a long-term contraceptive – it has an effect of up to 10 years – and also an emergency contraceptive if it is placed in the uterus within 5 days of sex. It can work better than pills. Less than 0.1% of women choose to place a pregnant contraceptive ring. This means fewer than 1 in 1,000 women using DCTC because emergency contraception will get pregnant.

DCTC must be equipped by a healthcare professional within 5 days (120 hours) after uns protected sex or, if it is possible to estimate when you ovulate, up to 5 days after ovulation.

4. Side effects

Side effects of using emergency contraceptive pills are similar to oral contraceptives, such as nausea and vomiting, uneven vaginal bleeding, and fatigue. Side effects are uncommon, they are mild and will usually cure themselves without taking additional medication.

If vomiting occurs within 2 hours after taking a dose, this dose should be repeated. Anti-vomiting medications should not be used regularly before taking emergency contraceptives.

The drug used for emergency contraception does not harm future fertility. There are no delays in returning to fertility after taking the emergency contraceptive pill.

Nausea is a sign of stomach pain.

Nausea is a side effect after using the drug

5. In situations where emergency contraception can be used?

Emergency contraception can be used in some situations after sexual contact. Include:

  • When having sex do not use contraception.
  • Sexual assault when the woman is not protected by an effective contraceptive. When there are concerns about possible contraception, from improper or improper use, such as: broken, slipped, or incorrectly used condoms;
  • Consecutive missed oral contraceptives such as

+ 3 hours later than the time of taking progestogen-only pills (minipill), or more than 27 hours after taking the previous drug;

+ 12 hours later than the normal desogestrel-containing medication time (0.75 mg) or more than 36 hours after taking the previous pill;

+ More than 2 weeks late for progestogen norethisterone enanthate (NET-EN);

+ More than 4 weeks late for drugs containing only progestin-depot-medroxyprogesterone acetate (DMPA);

+ More than 7 days late for combined injectable contraception (CIC).

Dr Pham Thi Yen has 11 years of experience in examination and treatment in the field of Obstetrics and Gynecology. Doctors with strengths and insights in:

  • Examination and consultation of common pregnancies, pathology pregnancies, high-risk pregnancies
  • Examination and treatment of gynecologic diseases: cervical inflammation, cervical glands
  • Laparoscopic surgery of gynecological diseases : extra-uterine pregnancy, uterine tumor , ovarian tumor
  • Surgery for breast tumors, vaginal, cervical tumors
  • Obstetric surgery : pregnancy surgery, examination
  • Treatment of female endormonal disorders of all ages: puberty, reproduction age; pre-menopause.

For direct advice, please click hotline number or register online HERE. In addition, you can register for remote consultation HERE

Source reference articles:,,, NCBI


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About: John Smith

b1ffdb54307529964874ff53a5c5de33?s=90&r=gI am the author of I had been working in Vinmec International General Hospital for over 10 years. I dedicate my passion on every post in this site.


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