Emergency Contraceptive Pills

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Emergency Contraceptive Pills




Generic NameBrand Name
levonorgestrelPlan B, NorLevo

Combination birth control pills

Generic NameBrand Name
estrogen and progestin Alesse, Aviane, Min-Ovral, Ovral

Levonorgestrel, such as Plan B and NorLevo, is specially packaged for emergency contraception. You can buy this medicine in most drugstores without a prescription.

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 (Plan B), you take both pills at the same time.

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

For most regular birth control pills, you take one dose of 2 to 5 pills as soon as you can. Then you take a second dose 12 hours later. The dose depends on the type of pill.

You can take emergency contraception up to 5 days after unprotected sex. But it works best if you take it right away or within 48 hours.

Intrauterine device (IUD)

As another option, a copper intrauterine device (IUD) can be inserted within 5 to 7 days after unprotected sex.

Generic Name
Nova-T or Flexi-T 300 (intrauterine device)

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.

A copper IUD makes the uterus and fallopian tubes produce fluids that kill sperm and prevent fertilization. These fluids contain white blood cells, copper ions, enzymes, and prostaglandins.2 As emergency contraception, a copper IUD also prevents an already fertilized egg from implanting in the uterus.1

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 are raped. 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 75% of pregnancies.3
  • The copper IUD is more than 99% effective. Only about 2 women out of 1,000 who use it for emergency contraception will get pregnant.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

Hormonal methods of emergency contraception

Side effects of hormonal methods include the following:

  • Nausea or vomiting is most likely when using special doses of birth control pills with estrogen plus progestin. Non-prescription antinausea medicines, such as Gravol or Pepto-Bismol, can prevent or reduce nausea. Levonorgestrel is a progestin-only pill that seldom causes nausea, so antinausea medicine is not usually recommended.
    • 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.
  • Some women have breast tenderness, fatigue, headache, abdominal pain, or dizziness 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.

IUD method of emergency contraception

Side effects during the first few days after having an IUD inserted include:

  • Uterine cramping.
  • Vaginal bleeding.

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 carry emergency contraception prescriptions based on their personal beliefs. If this happens to you, ask for the location of a pharmacist who sells emergency contraception, or see:

  • Your nearest public health clinic.
  • The Canadian Federation for Sexual Health (CFSH) Web site at www.cfsh.ca. Or call the CFSH national emergency contraception toll-free information line at 1-888-270-7444.
  • The Society of Obstetricians and Gynaecologists of Canada's (SOGC) emergency contraception information online at www.sogc.org/health/contraception-emergency_e.asp.


All of the methods for emergency contraception effectively prevent an unintended pregnancy after unprotected sex. Each has different advantages.

  • Experts recommend levonorgestrel, such as Plan B or NorLevo, for emergency contraception. It requires fewer pills and is less likely to cause nausea and vomiting. Also, it is slightly more effective than pills with both estrogen and progestin in them.
  • Women who can't take estrogen for health reasons are advised to use levonorgestrel.
  • Emergency contraception and estrogen-progestin do not help or hurt an embryo if you are already pregnant.1
  • Insertion of a copper-bearing IUD is the most effective and the most expensive emergency method.


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 you have a history of blood clots, use levonorgestrel, which is a progestin-only pill. (Estrogen makes blood clots more likely.)
  • If you are having a migraine headache at the time that you need emergency contraception, use levonorgestrel. Use of estrogen-progestin is not recommended. (Estrogen can start migraines or make them worse.)

If hormonal emergency contraception does not work and a pregnancy develops and grows, there is no known risk to the embryo.1


  • If you have a pelvic infection, including any kind of sexually transmitted infection (STI), an IUD is not the right emergency contraception for you. Inserting an IUD can spread infection into your uterus and fallopian tubes, causing pelvic inflammatory disease.
  • If you have been pregnant for 5 to 7 days or longer, inserting an IUD is dangerous. It can cause a miscarriage and a serious infection in the uterus (septic abortion).

In countries other than Canada, these emergency contraception choices and other choices may be available or regulated differently.

If emergency contraception is not available or you are early in an unplanned pregnancy, talk to your doctor about medical pregnancy care options and/or abortion as soon as possible.

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



  1. Stewart F, et al. (2007). Emergency contraception. In RA Hatcher et al., eds., Contraceptive Technology, 19th ed., pp. 87–112. New York: Ardent Media.
  2. Grimes DA (2007). Intrauterine devices (IUDs). In RA Hatcher et al., eds., Contraceptive Technology, 19th ed., pp. 117–143. New York: Ardent Media.
  3. American College of Obstetricians and Gynecologists (2005, reaffirmed 2007). Emergency contraception. ACOG Practice Bulletin No. 69. Obstetrics and Gynecology, 106(6): 1443–1452.


By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Primary Medical Reviewer Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer Kirtly Jones, MD, MD - Obstetrics and Gynecology
Last Revised July 6, 2010

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.