Progestin for Emergency Contraception

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Progestin for Emergency Contraception




Generic NameBrand Name
levonorgestrelPlan B, Plan B One-Step, Next Choice

Levonorgestrel, such as Plan B or Next Choice, is specially packaged for emergency contraception. You can buy this medicine in most drugstores.

  • If you are 17 or older, you can get emergency contraception from a pharmacist, without a prescription. Bring proof of your age.
  • If you are younger than 17, you can get emergency contraception with a prescription from a doctor.

Emergency contraception is used after unprotected sex to prevent a pregnancy from starting. It is most effective when it is used as soon as possible after intercourse. It is not necessary to take a pregnancy test before using emergency contraception.

How to take emergency contraception

Birth control experts recommend having emergency contraception pills, or a prescription for them, on hand in case you ever need them.  Emergency contraception is most effective when used as soon as possible after unprotected sex. Your risk of becoming pregnant increases as time passes.

For the emergency contraception option that contains 2 pills, you can take both pills at the same time. Or you can take 1 pill right away and the second pill 12 hours later.

There is also a one-pill emergency contraception option that lets you take the dose you need in just 1 pill.

You can take emergency contraception up to 5 days after unprotected sex. But it works best if you take it right away.

How It Works

Emergency contraception pills work by preventing ovulation, fertilization, or implantation.

Emergency contraception hormones may prevent fertilization by stopping the ovary from releasing an egg (ovum). They also make the fallopian tubes less likely to move an egg toward the uterus. Emergency contraception is also thought to thin the lining of the uterus, or endometrium. The thickened endometrium is where a fertilized egg would normally implant and grow.

Emergency contraception does not protect against sexually transmitted infections (STIs).

Why It Is Used

Emergency contraception is meant to be used as a backup method for preventing pregnancy. For regular protection, be sure that you have:

  • A birth control method that you know you can use every time you have sex.
  • Condoms for protection from sexually transmitted infections (STIs) every time you have sex.

You can use emergency contraception if you are not confident that you were protected against pregnancy during intercourse. This can happen if:

  • You have unplanned sex without birth control.
  • Your usual birth control method fails. For example:
    • A barrier method, such as a condom or diaphragm, has torn or dislodged.
    • You have missed taking birth control pills.
    • An IUD has come out, either completely or partially.
  • You are taking other medicines that may affect contraception medicines. These include some antiseizure, antibiotic, and antifungal medicines, and the herb St. John's wort.
  • You were sexually assaulted. Some emergency rooms offer emergency contraception as part of sexual assault care. Others will provide emergency contraception when they are asked for it.

Be sure to plan with your doctor for your birth control needs.

How Well It Works

Emergency contraception effectiveness varies according to the method used.

  • Emergency contraception, such as Plan B, can prevent nearly 74% of pregnancies.1
  • Plan B is more effective when used for emergency contraception than combined birth control pills (estrogen and progestin).

The sooner pills are used after unprotected sex, the more likely they are to prevent pregnancy.

Side Effects

Side effects may include the following:

  • Nausea or vomiting. If you get nauseous, nonprescription antinausea medicines, such as Dramamine or Pepto-Bismol, can prevent or reduce nausea.
    • Caution: If you vomit within 2 hours of taking a dose, call your doctor for advice. You may need to repeat the dose.
  • Pregnancy is possible after using emergency contraception. Although your next period may be slightly late, a delay of 3 weeks or longer may be a sign of pregnancy. If this happens, call your doctor to see whether you need a pregnancy test.
  • Breast tenderness, fatigue, headache, abdominal pain, and/or dizziness are possible after taking emergency contraception.

Call your doctor if side effects, such as headache, dizziness, or belly pain, continue for longer than 1 week after using emergency contraception.

See your doctor if you do not have your period within 21 days after using emergency contraception.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Some pharmacists refuse to fill emergency contraception prescriptions based on their personal beliefs. If this happens to you, ask for the location of a pharmacist who will fill the prescription, or contact:

  • The Emergency Contraception website
  • The Planned Parenthood clinic nearest you, or call 1-800-230-PLAN (1-800-230-7526).

Emergency contraception use is not recommended if you know or suspect you are already pregnant. If you may already be pregnant, see your doctor.

If hormonal emergency contraception does not work and a pregnancy develops and grows, there is no known risk to the embryo.2

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. American College of Obstetricians and Gynecologists (2010). Emergency contraception. ACOG Practice Bulletin No. 112. Obstetrics and Gynecology, 115(5): 1100–1109.
  2. Stewart F, et al. (2007). Emergency contraception. In RA Hatcher et al., eds., Contraceptive Technology, 19th ed., pp. 87–112. New York: Ardent Media.


ByHealthwise Staff
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
Specialist Medical ReviewerFemi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology
Last RevisedMay 4, 2012

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