Plan B dosage, forms, and strengths

Plan B One-Step is an over-the-counter emergency oral contraceptive. Also called the “morning-after pill,” it’s intended to reduce the risk of pregnancy after unprotected sex or in situations where another method of birth control has failed. A single dose of Plan B One-Step must be taken within 72 hours of unprotected sex. The sooner it’s taken, the more effective it is at preventing pregnancy. The active ingredient in Plan B One-Step is levonorgestrel, a drug that acts like a natural female hormone to delay ovulation and reduce sperm motility.

Plan B forms and strengths

Plan B One-Step is only available in one dosage form.

• Tablets: 1.5 mg levonorgestrel

Plan B dosage for adults

Plan B One-Step helps prevent pregnancy in women who have had unprotected intercourse, when contraception has failed (such as a condom breaking), or when a woman misses one or more birth control pill doses. 

The single dose must be taken within 72 hours of the sexual encounter. When taken within that 72-hour window, the dose will reduce the risk of pregnancy by up to 84%, according to the initial clinical trials.

The active ingredient in Plan B One-Step is levonorgestrel, a progestogen. It’s a synthetic drug that works like progesterone in the body. Among those effects, levonorgestrel blocks the release of an egg from the ovaries and thickens mucus in the cervix. In a woman who hasn’t yet ovulated, levonorgestrel prevents pregnancy by blocking the release of a viable egg and decreasing sperm motility. When taken past ovulation, levonorgestrel decreases sperm motility and makes it less likely the sperm will pass into the uterus.

Some people cannot take Plan B One-Step, including those with allergies to the drug, severe liver disease, or women who are pregnant. Plan B should not be used in place of regular birth control. 

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Plan B dosage for children

Plan B One-Step is FDA-approved for women of all ages who have had their first period. The dosage is the same for children and adults. 

Plan B can be purchased without a prescription in all 50 states by adults and children. No age or identification is required.

Plan B dosage restrictions

Plan B One-Dose has no dosage restrictions for liver impairment, kidney disease, or any other medical condition. 

However, women who are allergic to levonorgestrel, allergic to any of the inactive ingredients in the drug, or have severe liver disease should never take Plan B One-Step. The drug is also contraindicated in pregnant women, postmenopausal women, young women who haven’t yet had their first period, and men. 

How to take Plan B

Plan B One-Step must be taken within 72 hours of unprotected sex or failed contraception to be effective. Only one dose is required. 

• Take the Plan B pill as soon as possible.

• Wait to remove the tablet from the blister pack until ready to take it.

• Plan B can be taken with or without food.

• Swallow the tablet whole with a drink of water.

• If you vomit within two hours of taking the dose, contact a healthcare professional about taking a second dose.

• Store Plan B at room temperature, but take the pill as soon as possible. 

• Discard after the expiration date on the package.

Plan B dosage FAQs

How long does it take Plan B to work?

The levonorgestrel in Plan B begins to work soon after it’s swallowed. The drug hits its peak concentration in the blood about 2 hours after being taken. 

How long does Plan B stay in your system?

On average, it takes the body about 27.5 hours to eliminate half a dose of levonorgestrel from the system. That means that it will only work for one instance of unprotected sex. 

What happens if I miss a dose of Plan B?

Take the Plan B pill as soon as possible after unprotected sex or contraception failure. If you forget, the drug is only considered effective when taken within 72 hours after unprotected sex. After that, the risk of pregnancy goes up.

How long can you take Plan B?

Plan B One-Step can be safely used as needed. However, it is not effective as a regular form of birth control. If frequent unprotected sex is an issue, then get medical advice about regular birth control.

How do I stop taking Plan B?

Plan B One-Step is a single-dose medication. It can be stopped after one dose without causing withdrawal or dependence.

What is the maximum dosage for Plan B?

The maximum dosage for Plan B is a single 1.5 mg levonorgestrel pill taken as emergency contraception.

Can you overdose on Plan B?

An overdose is unlikely because Plan B is purchased as a single pill. Healthcare professionals don’t know what an overdose will do. If too many pills are taken or someone accidentally takes a Plan B tablet, contact a poison helpline or visit an emergency department. 

What interacts with Plan B?

Although Plan B One-Step is an OTC medication, talk to the pharmacist or other healthcare professional if you take other prescription drugs, over-the-counter medications, vitamins, supplements, or herbal remedies. Some drug interactions can make Plan B less effective at preventing pregnancy, so you’ll want to know if you’re taking one of these drugs or supplements before using Plan B. These include:

• Barbiturates

• Drugs that treat seizures (carbamazepine, oxcarbazepine, topiramate, and phenytoin)

• The antibiotic rifampin

• The antifungal drug griseofulvin

• The high cholesterol treatment felbamate

• Drugs that treat HIV/AIDS

• The herbal supplement St. John’s wort

Does Plan B affect regular birth control pills?

Plan B One-Step does not interfere with regular birth control pills. Continue to take oral contraception after taking the Plan B pill following the current schedule unless you’ve missed enough doses that you need to start over. For restarting the birth control schedule, consult the prescribing information that comes with the birth control pills. If you are not on regular birth control when you use Plan B, you can start taking combination or progestin-only birth control pills immediately at any point in the menstrual cycle.

What happens when you mix Plan B and alcohol?

There are no known interactions between Plan B and alcohol. 

Is it safe to take Plan B during pregnancy?

Pregnant women should not take Plan B One-Step. There is no evidence that it’s unsafe, but it cannot end an existing pregnancy.

Is it safe to take Plan B while breastfeeding?

Plan B One-Step can be taken by women who are breastfeeding. The levonorgestrel in the pill will show up in breast milk but in a small amount, not enough to affect the nursing infant or cause adverse reactions.

Are there side effects of Plan B?

Plan B One-Step is likely to cause some adverse effects. The most common side effects are menstrual changes (heavier or lighter periods), nausea, lower abdominal pain, fatigue, headache, dizziness, and breast tenderness.

Does Plan B affect fertility?

Plan B One-Step only affects ovulation for a short period after the pill is taken. It does not affect ovulation or fertility in the future.

Does Plan B prevent sexually transmitted diseases?

Levonorgestrel emergency contraceptives will not prevent STDs, including HIV/AIDS. If there are any concerns about STDs, use barrier methods of birth control and get tested regularly.

What happens if the next period is missed?

One of the side effects of Plan B is to delay menstrual bleeding in some women. However, Plan B One-Step is not 100% effective at preventing pregnancy. If the next period is at least seven days late, get a pregnancy test.

When should I see a healthcare professional?

If you miss a period and test positive for pregnancy, see a healthcare professional. If you have severe abdominal pain, it may be due to an ectopic pregnancy. See a healthcare provider as soon as possible.

Sources

• Levonorgestrel, StatPearls

• Plan B One-Step, Foundation Consumer Healthcare

• Plan B One-Step levonorgestrel tablet prescribing information, FDA (Food and Drug Administration)

• Plan B One-Step levonorgestrel tablet drug information, DailyMed (NIH National Library of Medicine)