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Progestin for Emergency Contraception

Table of Contents

Progestin for Emergency Contraception




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

Levonorgestrel is specially packaged for emergency contraception. You can get emergency contraception without a prescription at most drugstores.

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:

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

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.

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

Side Effects

Side effects may include the following:

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:

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) 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.

Other Works Consulted

Credits for Progestin for Emergency Contraception

By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer Femi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology
Last Revised August 7, 2013

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