Like other birth control methods, emergency contraceptive pills help prevent pregnancy after unprotected sex. How do they work, and when should you take them? Read on for a clear guide.

What are Emergency Contraceptive Pills?

Emergency contraceptive pills are taken after unprotected sex or when a regular contraceptive method fails. As the name suggests, they are intended for urgent situations only.

These pills contain a progestin-like hormone that prevents or delays ovulation and helps keep sperm from reaching an egg for fertilization.

Two contraceptive pills are commonly used are levonorgestrel and ulipristal acetate. Levonorgestrel can lower the chance of pregnancy after unprotected sex, but it does not protect women against sexually transmitted infections. Its effectiveness may be reduced in people with certain body weights, such as women that weighs more than 74 kg.

Ulipristal acetate also helps to prevent pregnancy but does not protect women against sexually transmitted infections. Its effectiveness may be lower in people with a body mass index (BMI) over 30.

Emergency contraceptive pills do not end an existing pregnancy. If you are already pregnant, these pills will not have an effect.

When Should You Use Emergency Contraceptive Pills?

Use emergency contraceptive pills in situations such as:

• Not using a condom during intercourse

• Not using any birth control during intercourse

• Miscalculating your cycle and having sex during your fertile window

• Not using a contraceptive method as directed

• A condom that expired, tore, or slipped off during sex

• Failure to withdraw penis in time, with possible ejaculation inside the vagina

• Forgetting to use spermicide or a diaphragm

• Premature ejaculation

• Recent sexual assault

Some emergency contraceptive pills are available over the counter without a prescription. Always read and follow the directions on the package.

You can take emergency contraceptive pills with or without food. They work best when taken as soon as possible, and they can reduce the risk of pregnancy by about 75–99% if taken within 72 hours of unprotected sex.

Side Effects of Emergency Contraceptive Pills

Possible side effects include:

• Nausea or vomiting

• Dizziness

• Fatigue

• Headache

• Breast tenderness

• Bleeding between periods or heavier bleeding

• A delayed period

• Lower abdominal cramps

Your next period may differ from usual; it can arrive earlier or later, and flow can be heavier. See a doctor if your period is more than 7 days late or if you notice symptoms of a sexually transmitted infection.

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