Usage Information
Description and Dosage
Not actual size

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


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

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

Significant changes (increase or decrease) in the plasma levels of progestin have been noted in some cases of co-administration with HIV protease inhibitors or with non-nucleoside 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.