Emergency Contraception: Mechanism Effectiveness Side Effects by NJE


Emergency contraception (EC) can prevent pregnancy soon after unprotected intercourse, sexual assault, or failure or improper use of a birth control method. EC reduces the risk of pregnancy when used up to 120 hours (5 days) after unprotected sex but is more effective if used earlier.


The primary mechanism of all EC pills is inhibition or delay of ovulation. Emergency insertion of the copper IUD may prevent fertilization or implantation.


The copper IUD prevents 99% of expected pregnancies and should be considered the first-line option for all women of childbearing age. Oral ulipristal acetate and levonorgestrel prevent the majority of pregnancies after unprotected intercourse. Ulipristal acetate is more effective than levonorgestrel, particularly in overweight and obese patients.


Morning-after pill, postcoital contraception EC 


Approximately 49% of all pregnancies and more than 82% of teen pregnancies in the U.S. are unintended. An estimated 1.7 million unintended pregnancies could be prevented annually if EC use were widespread.



• If there is doubt about whether a patient is already pregnant from intercourse that occurred more than 2 weeks previously, a pregnancy test may be helpful. However, there is no need for a pregnancy test before administering EC pills. Delays in the administration of the medication will reduce its efficacy. The medication in EC pills will not harm an established pregnancy.

• A pregnancy test should be done before the insertion of a copper IUD.



• Administer EC as soon as possible after unprotected intercourse. All forms of EC reduce the risk of pregnancy when used up to 5 days after unprotected intercourse but are more effective if used earlier. EC pills function by delaying ovulation, so it is important to counsel patients to abstain or use a barrier method for 2 weeks following EC use in order to avoid a later-cycle pregnancy.

• Copper IUD for Emergency Contraception

1. Emergency insertion of the copper IUD is the most effective option for EC.

2. Ideal for women who desire effective long-term contraception and have no contraindications to IUD insertion.

3. A pregnancy test should be done before IUD insertion.

4. Requires insertion by a clinician.

5. Some women may experience changes in bleeding patterns that are bothersome to them.

• Emergency contraceptive pills.

1. Ulipristal acetate (Ella)

• Single dose 30 mg ulipristal acetate, a progesterone-receptor modulator.

• More effective than levonorgestrel EC. Prescription is required.

2. Levonorgestrel (Next Choice, Plan B One-Step)

• Total dose 1.5 mg levonorgestrel.

• A single dose is equally effective and causes no more side effects than two divided doses.

• Less effective in overweight and obese women (BMI >25). Available over the counter without a prescription for all ages. Providing a prescription may decrease the cost of the medication, especially for Medicaid recipients.

3. Combined estrogen/progestin contraceptive pills:

1. Least effective method with highest incidence of side effects.

2. Two doses, 12 hours apart, of 100 to 120 mcg Ethinyl estradiol and 0.5 to 0.6 mg of levonorgestrel (or 1.0 to 1.2 mg of norgestrel) per dose.

3. Prescription is required, but if patient uses combined oral contraceptives, she may have the product on hand.

4. The Emergency Contraception website provides instructions for using available combined oral contraceptive pills for EC.

• Side effects of Emergency Contraception

1. Combined estrogen-progestin EC will cause nausea in 50% of women and vomiting in 20%. Side effects resolve within 1 to 2 days. Antinausea medication such as meclizine 25 mg orally is recommended 1 hour before taking combined estrogen-progestin EC. It can be used on an as-needed basis with the other EC methods.

• Contraindications of Emergency Contraception

1. Few contraindications to EC exist other than hypersensitivity to the product. EC pills will not affect an established pregnancy.

2. There are no other evidence-based medical contraindications to the use of EC pills. The benefits of EC in preventing pregnancy generally outweigh the theoretical risks for women with contraindications to long-term use of combined hormonal contraception, such as thromboembolic disease, smoking after age 35 years, heart disease, or liver disease. Non–estrogen-containing EC is preferable for all women because of better efficacy but particularly for those with any of these conditions or who are breastfeeding.

CHRONIC Rx of Emergency Contraception

Because EC pills are less effective than other forms of contraception, they are not recommended as an ongoing method of contraception. The copper IUD is highly effective for EC and can be kept in place to prevent pregnancy for up to 12 years.

DISPOSITION of Emergency Contraception

After using EC, most women will have their menses within 1 to 2 weeks of the expected date. If a woman’s next expected menses are delayed by more than 3 weeks, a pregnancy test should be done.




• Copper IUD is the most effective form of EC and is the only method that provides users with long-term contraception.

• All forms of EC pills reduce the risk of pregnancy up to 5 days after unprotected intercourse, with ulipristal acetate being the most effective pill. Delayed ovulation can result in a later-cycle pregnancy, so patients should use a barrier method for 2 weeks following EC pill use.

• The copper IUD is highly effective regardless of BMI. EC pills are less effective in overweight and obese women, but the weight at which they lose efficacy is unclear and may vary between women. Therefore, regardless of BMI, all EC methods should be offered to all women with appropriate counseling that some forms may be less effective with higher BMI. Ulipristal acetate is more effective than levonorgestrel, particularly in overweight and obese women.

• A pregnancy test is not necessary before administering EC pills because the medicines will not harm an existing pregnancy.

• Advanced prescription of EC pills at routine visits may increase timely use of EC and does not decrease the use of more reliable means of contraception. Health care providers who speak with the pharmacist directly are more likely to ensure timely distribution of EC pills to their patients.


• Patients should begin an effective method of birth control immediately after using EC. Hormonal contraceptives can be started the day after EC is administered. Abstinence or a barrier method should be used for 2 weeks.

• EC should be offered to all women after sexual assault. 


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