Emergency contraception is used to prevent a woman from getting pregnant after she has had sex without using birth control or if her current method fails.

This page explains:


To understand how emergency contraception works, you should know what happens during reproduction. A woman has two ovaries, one on each side of the uterus. Each month, one of the ovaries releases an egg into a fallopian tube. This is called ovulation. It typically occurs about 12–14 days before the start of the menstrual period.

Each month during ovulation, an egg is released (1) and moves into one of the fallopian tubes (2). If a woman has sex around that time, an egg may meet a sperm in the fallopian tube, and the two may join (3). This is called fertilization. The fertilized egg then moves through the fallopian tube in the uterus (4).

A woman can get pregnant if she has sex around the time of ovulation. During sex, the man ejaculates sperm into the vagina. The sperm travel up through the cervix and into the fallopian tubes.

If a sperm meets an egg in the fallopian tube, fertilization—union of egg and sperm—can occur. The fertilized egg moves down the fallopian tube to the uterus. It then attaches to the uterus and grows into a fetus.

About Emergency Contraception

Two methods of birth control can be used for emergency contraception. The most commonly used method is pills (also known as the “morning-after pill”). Birth control pills contain the hormones estrogen and progestin or, in some cases, progestin only. The progestin-only method is more effective and is less likely to cause nausea. The intrauterine device (IUD) also can be used for emergency contraception. It must be inserted by a doctor.

The IUD for Emergency Contraception

The IUD can be used as emergency contraception. It works best if inserted within 5 days of having unprotected sex. The presence of the IUD prevents the fertilized egg from attaching to the wall of the uterus.

A benefit of the IUD is that it can be left in for long-term use. The IUD may be a good choice if you cannot take birth control pills. The IUD does not prevent sexually transmitted diseases.

How It Works

The hormones in emergency contraception pills disrupt the normal patterns in a woman’s menstrual cycle. Depending on where a woman is in her menstrual cycle and when the pills are given, these pills may:

Taken correctly, emergency contraception can be an effective way to prevent pregnancy. On average, about 8 out of 100 women become pregnant when they have sex without using birth control. Emergency contraception can reduce this risk by at least 75%. This means that only 2 women out of 100 women will get pregnant if they take emergency contraception correctly after having unprotected sex. A woman may use emergency contraception in some of the following situations:

Although emergency contraception is a good option for preventing pregnancy when a woman has unprotected sex, it should not be used on a routine basis. Regular use of a birth control method (such as condoms or birth control pills) is most effective.

How to Get It

If you are aged 18 years or older, emergency contraception can be bought in many places, including drugstores, without a prescription by asking the pharmacist. If you are younger than 18 years and need emergency contraception, call your doctor’s office or go to a family planning clinic or hospital emergency room. Tell them you need treatment right away. Your doctor can call in a prescription to a drugstore for you or you can get it directly from a pharmacy. You also can call the Emergency Contraception Hotline (888- NOT-2-LATE) to find a doctor who will provide you with a prescription. Many doctors will give you an advance prescription for emergency contraception. This way, you will have it on hand if you need it.

How to Take Emergency Contraception

Emergency contraception pills may be prescribed in one of two forms:

  1. A specific dosage of regular birth control pills (contains estrogen and progestin)
  2. A package with two pills (contains progestin only)

The pills are given in two doses. To prevent pregnancy, the first dose of pills must be taken by mouth as soon as possible, ideally within 3 days (72 hours), but no later than 5 days (120 hours) of having unprotected sex. A second dose is taken 12 hours after the first dose. The number of pills in the dose depends on the brand of pill used. For progestin-only pills, both doses can be taken at the same time or 12–24 hours apart.

Side Effects

Some nausea and vomiting may occur after taking the pills. Your doctor may give you a medicine to prevent nausea. If you vomit within 2 hours of taking either dose, you may need to repeat that dose. Your next period may not occur at the expected time. You may bleed or spot in the week or month after the treatment. Other side effects may include:

Any of these side effects will go away within a few days.

Follow-up Care

Emergency contraception can greatly reduce a woman’s risk of getting pregnant after having unprotected sex. However, there is still a chance you could become pregnant. If you take a pregnancy test and the result is positive, talk to your doctor. Emergency contraception does not harm a pregnancy or the health of the baby.

If you have sex after you use emergency contraception pills, you should use another contraception method, such as a condom, until you have your next period. After that you should talk to your doctor about using a reliable form of birth control for as long as you wish to avoid pregnancy. If you were taking birth control pills before, you should keep taking the pills and use a backup method. If you have not had a period within a week of when you expect it, you should see your doctor for a pregnancy test. You also should see your doctor if you have lower abdominal pain or if you have bleeding or spotting that lasts longer than a week. These can be signs of a miscarriage or ectopic pregnancy.

Keep in mind that emergency contraception does not prevent sexually transmitted diseases (STDs). You should be tested or treated if you are at risk for an STD.

Finally . . .

Using birth control when you have sex is the best way to prevent unwanted pregnancy. Ask your doctor about a method of birth control that you can use regularly. However, if you do have sex without birth control, you can use emergency contraception. It is simple and safe. It can greatly reduce the chance of pregnancy after unprotected sex.


Ectopic Pregnancy: A pregnancy in which the fertilized egg begins to grow in a place other than inside the uterus, usually in the fallopian tubes.

Estrogen: A female hormone produced in the ovaries that stimulates the growth of the lining of the uterus.

Fetus: A baby growing in a woman’s uterus.

Intrauterine Device (IUD): A small device that is inserted and left inside the uterus to prevent pregnancy.

Miscarriage: Early pregnancy loss.

Progestin: A synthetic form of progesterone that is similar to the hormone produced naturally by the body.

Sexually Transmitted Diseases (STDs): Diseases that are spread by sexual contact, including chlamydial infection, gonorrhea, genital warts, herpes, syphilis, and infection with human immunodeficiency virus (HIV, the cause of acquired immunodeficiency syndrome [AIDS]).

Source: acog.org