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What Is Plan B?

Plan B is a name associated with levonorgestrel emergency contraception, which reduces the chance of pregnancy after unprotected sexual intercourse or contraceptive failure. The original two-tablet Plan B product has been discontinued in the United States. Its successor, Plan B One-Step, contains levonorgestrel 1.5 mg in a single oral tablet and is available over the counter without an age restriction. It is intended for emergency use rather than routine birth control. Plan B One-Step does not terminate an existing pregnancy and does not protect against sexually transmitted infections.

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What Is Plan B?

Plan B is a name associated with levonorgestrel emergency contraception, which reduces the chance of pregnancy after unprotected sexual intercourse or contraceptive failure. The original two-tablet Plan B product has been discontinued in the United States. Its successor, Plan B One-Step, contains levonorgestrel 1.5 mg in a single oral tablet and is available over the counter without an age restriction. It is intended for emergency use rather than routine birth control. Plan B One-Step does not terminate an existing pregnancy and does not protect against sexually transmitted infections.

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How Does Plan B Work?

Plan B One-Step contains levonorgestrel, a synthetic progestin that works primarily by preventing or delaying ovulation. When ovulation has not occurred, delaying the release of an egg can reduce the chance of fertilization after unprotected intercourse. Plan B One-Step does not work by disrupting implantation and does not affect an established pregnancy. Its effectiveness depends largely on how soon it is taken and whether ovulation has already occurred. The medication does not protect against pregnancy from intercourse occurring after the dose.

When Is Plan B Used?

Plan B One-Step is used after unprotected intercourse or when a contraceptive method fails, such as a condom breaking or missed birth control pills. It is intended to reduce the chance of pregnancy and works best when taken as soon as possible, preferably within 72 hours. Levonorgestrel emergency contraception may still have some effect when taken later, but effectiveness declines with delay. Other emergency contraception options can be more appropriate later in the five-day window or under certain clinical circumstances. Plan B is not an abortion medication and does not prevent HIV or other sexually transmitted infections.

How Should Plan B Be Taken?

Plan B One-Step is taken as one 1.5 mg levonorgestrel tablet orally as soon as possible after unprotected intercourse, preferably within 72 hours. It can be taken at any time during the menstrual cycle. If vomiting occurs within two hours, contact a healthcare professional about whether another dose is needed. Normal contraceptive use should continue or begin according to the selected method's instructions, with backup protection when appropriate. If the menstrual period is more than one week late, take a pregnancy test. Plan B One-Step should not replace regular contraception.

What Are the Side Effects and Warnings of Plan B?

Common side effects include nausea, lower abdominal discomfort, fatigue, headache, dizziness, breast tenderness, and changes in menstrual bleeding. The next period may arrive earlier or later than expected and can differ in flow. Severe abdominal pain after use requires medical evaluation because ectopic pregnancy must be considered if pregnancy occurs. Certain medications that induce liver enzymes can reduce levonorgestrel exposure and potentially decrease effectiveness. Plan B does not protect against sexually transmitted infections. It should not be used as a substitute for evaluation when pregnancy symptoms or persistent menstrual changes occur.

Common Questions About Plan B

Is Plan B available without a prescription?

Yes. Plan B One-Step is available over the counter in the United States without an age restriction. The original two-tablet Plan B product has been discontinued.

Does Plan B work after 72 hours?

Levonorgestrel emergency contraception may retain some effectiveness after 72 hours, but it becomes less reliable with time. A healthcare professional can discuss alternatives suitable for use within five days.

Does Plan B cause an abortion?

No. Plan B One-Step primarily works by preventing or delaying ovulation. It does not interrupt an established pregnancy.

Can Plan B delay the next menstrual period?

Yes. The next period can arrive earlier or later than expected. A pregnancy test is recommended if menstruation is more than one week late.

References

DailyMed - PLAN B ONE-STEP (levonorgestrel) tablet. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=fcc7ba8e-ad54-4efe-87e4-5eb0fbf4f064. Date Accessed November 2, 2026.

Emergency Contraception. Centers for Disease Control and Prevention. https://www.cdc.gov/contraception/hcp/usspr/emergency-contraception.html. Date Accessed November 2, 2026.

Levonorgestrel. MedlinePlus. https://medlineplus.gov/druginfo/meds/a610021.html. Date Accessed November 2, 2026.

Levonorgestrel (Plan B One-Step). MotherToBaby. https://www.ncbi.nlm.nih.gov/books/NBK583410/. Date Accessed November 2, 2026.

Plan B One-Step (1.5 mg Levonorgestrel) Information. U.S. Food and Drug Administration. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/plan-b-one-step-15-mg-levonorgestrel-information. Date Accessed November 2, 2026.