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Plan B One-Step is supplied as a white, round tablet containing 1.5 mg of levonorgestrel.


Plan B One-Step is a single pill that is taken by mouth. It must be taken within 72 hours (3 days) after unprotected sex or birth control failure to help prevent pregnancy. Plan B One-Step should be taken as soon as possible after intercourse. The sooner it’s taken, the better it works.

Your patient should resume her regular method of contraception right away — or start one, if she doesn’t have a regular method — since Plan B One-Step does not protect against additional incidents of unprotected sex.

When it should not be taken

Plan B One-Step should not be taken:

  • If a woman is already pregnant, because it won’t work
  • If she is allergic to levonorgestrel or any of the ingredients in Plan B One-Step
  • As a regular birth control method, because it is not as effective

Plan B One-Step does not protect against HIV/AIDS or other STIs.

Drug Interactions

Drugs or herbal products that induce progestin-metabolizing enzymes, including CYP3A4, may decrease the plasma concentrations of progestins, and decrease the effectiveness of progestin-only pills.

Some drugs or herbal products that may decrease the effectiveness of progestin-only pills include:

  • barbiturates
  • bosentan
  • carbamazepine
  • felbamate
  • griseofulvin
  • oxcarbazepine
  • phenytoin
  • rifampin
  • St. John’s wort
  • topiramate
  • certain HIV/AIDS medications

Significant changes (increase or decease) in the plasma levels of progestin have been noted in some cases of coadministration with HIV protease inhibitors or with nonnucleoside reverse transcriptase inhibitors (NNRTIs).

Consult the labeling of all concurrently used drugs to obtain further information about interactions with progestin-only pills or the potential for enzyme alterations.

Safety and possible side effects

When taken as directed, Plan B One-Step is generally safe for women. Some women will have side effects that include:

  • menstrual changes
  • nausea
  • lower stomach (abdominal) pain
  • tiredness
  • headache
  • dizziness
  • breast tenderness
  • vomiting

Some women taking Plan B One-Step will have menstrual changes such as spotting or bleeding before their next period. Some women may have a heavier or lighter next period, or a period that arrives earlier or later than usual. If the patient’s period is more than a week late, she may be pregnant and should be tested.

If the patient has severe abdominal pain, she may have an ectopic pregnancy, and should get immediate medical attention.

If the patient vomits within 2 hours of taking the Plan B One-Step tablet, the patient should immediately contact a healthcare professional to find out if she should repeat the dose. It is up to the healthcare professional’s clinical judgment whether or not the patient should repeat the one-tablet dose.

Plan B One-Step is a registered trademark of Foundation Consumer Healthcare. PBO-40759 June 2017. This site is intended for US audiences only.