Generic name: levonorgestrel emergency contraceptive [ LEE-voe-nor-jes-trel ]
Dosage form: tablet (1.5 mg)
Drug class: Contraceptives

Medically reviewed by Melisa Puckey, BPharm. Last updated on May 13, 2025.

What is Plan B?

Plan B is an over-the-counter emergency contraceptive pill used to help prevent pregnancy after unprotected sex or contraceptive failure, including a broken condom, missed birth control pills. Plan B (levonorgestrel) works by temporarily delaying ovulation (the release of an egg), which helps prevent pregnancy before it can happen.

Plan B is most effective when taken as soon as possible, within 72 hours (3 days) of unprotected sex. While it's often called the "morning-after pill," it can be taken any time within that 72-hour window.

Anyone, regardless of age or gender can purchase Plan B One-Step right off the shelf without a prescription or ID requirement at all major retailers in the U.S.

The Plan B pill is a backup method of preventing pregnancy and should not be used as a regular form of birth control. Talk with your doctor or healthcare professional about the many forms of birth control available.

Learn more: Emergency Contraception: What You Need to Know

How effective is Plan B?

According to a clinical trial, Plan B reduced the average chance of pregnancy from about 8% to 1.1% after a single act of unprotected sex during the most fertile part of the menstrual cycle, provided it was taken within 72 hours.

In a review of clinical trials, Plan B was shown to have an efficiency rate of 89% when taken correctly, as directed.

Learn more: What are the signs that Plan B didn't work?

Learn more: What's the weight limit for Plan B?

How does Plan B work? 

Plan B contains a hormone called levonorgestrel (1.5mg). It works by blocking the surge of luteinizing hormone, which typically happens before ovulation occurs (when your ovary releases an egg). This delays or stops ovulation. Additionally, Plan B thickens cervical mucus, which affects how well sperm can move and reach the released eggs. These actions help prevent fertilization of an egg so that pregnancy cannot occur.

Learn more: Does Plan B work during ovulation?

Plan B side effects

Common Plan B side effects

Common Plan B side effects can include: 

• stomach pain;
• breast pain or tenderness;
• nausea, vomiting, diarrhea;
• headache, dizziness;
• feeling tired; or
• changes in your menstrual periods, including your period being earlier or later than expected. Learn more: Can Plan B make your period late or cause bleeding?

Serious Plan B side effects

Allergic reaction: Get emergency medical help if you have signs of an allergic reaction to this medicines. Symptoms may include hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Tubal (ectopic) pregnancy: Call your doctor or seek emergency medical help if you have severe pain in your lower stomach or side. This could be a sign of a tubal pregnancy (a pregnancy that implants in the fallopian tube instead of the uterus). A tubal pregnancy is a medical emergency that needs medical treatment immediately.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Related/similar drugs

Warnings

Do not use this medicine if you are already pregnant. Levonorgestrel will not terminate a pregnancy that has already begun (the fertilized egg has attached to the uterus).

Ask a doctor or pharmacist before taking levonorgestrel if you regularly use medication for seizures, tuberculosis, or HIV/AIDS. Certain medications can make levonorgestrel less effective as an emergency form of contraception.

Before taking this medicine

You should not use Plan B  if you are allergic to levonorgestrel or any of the ingredients in this medicine. A list of all ingredients is near the bottom of this page.

Pregnancy

Do not use this medicine if you are already pregnant. This medicine will not terminate a pregnancy that has already begun (the fertilized egg has attached to the uterus).

Breastfeeding

Levonorgestrel may slow breast milk production. Tell your doctor or healthcare professional if you are breastfeeding.

How should I take Plan B?

Take Plan B One-Step exactly as directed on the label, or as prescribed by your doctor or health professional.

Plan B One-Step (levonorgestrel 1.5 mg) is one tablet that is taken once.  It must be taken as soon as possible and no later than 72 hours (3 days) after unprotected sex.  The sooner the tablet is taken, the better it works.

Call your doctor right away if you vomit within 2 hours after taking this medicine, as you may need to take another tablet.

Visit your doctor within 3 weeks after taking this medicine. A doctor should confirm that you are not pregnant and that this medicine has not caused any harmful effects.

If your period is late by 1 week or longer after the expected date, you may be pregnant. Get a pregnancy test and contact your doctor if you are pregnant. Levonorgestrel will not terminate a pregnancy if the fertilized egg has attached to the uterus.

Plan B dosing information

• Plan B One-Step (levonorgestrel 1.5 mg) is one tablet that is taken within 72 hours (3 days) of unprotected sex. The sooner the tablet is taken, the more effective it is.
• Plan B contained two levonorgestrel 0.75 mg tablets and was taken as one tablet at once, followed by a second tablet 12 hours later. Plan B should be taken within 72 hours (3 days) of unprotected sex. This dose is now discontinued.

What happens if I miss a dose?

Since this medicine is used as a single dose, it does not have a daily dosing schedule.

What happens if I overdose?

Because this medicine is supplied as a single tablet in an exact strength, an overdose is unlikely to occur when this medicine is used as directed. Do not take more than one tablet at the same time.

What to avoid

This medicine will not protect you from sexually transmitted diseases--including HIV and AIDS. Using a condom is the only way to protect yourself from these diseases. Avoid having unprotected sex.

What other drugs will affect Plan B?

Certain other medications can make levonorgestrel less effective, which may result in pregnancy. Do not take this medicine without telling your doctor or pharmacist that you are using any of the following medications:

• efavirenz (Atripla, Sustiva);
• rifampin (Rifadin, Rifater, Rifamate, IsonaRif, Rimactane); or
• seizure medication--carbamazepine, felbamate, fosphenytoin, oxcarbazepine phenobarbital, phenytoin, primidone.
•  Bosentan
• Griseofulvin
• topiramate

This list is not complete. Other drugs may interact with levonorgestrel, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide, to check for interactions with Plan B click on the link below.       

Storage

Store tablet at room temperature 20–25°C (68–77°F)

What are the ingredients in Plan B?

Active ingredient: levonorgestrel 1.5 mg

Inactive ingredients: colloidal silicon dioxide, potato starch, magnesium stearate, talc, corn starch, lactose monohydrate

Manufacturer

Teva Women’s Health, Inc.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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