levonorgestrel (Plan B, Plan B One-Step)

Pharmacy Author:
Medical and Pharmacy Editor:

GENERIC NAME: levonorgestrel

BRAND NAME: Plan B, Plan B One-Step

DRUG CLASS AND MECHANISM: Levonorgestrel (Plan B) is emergency contraception (commonly called the morning after pill) that is used as backup contraception to prevent pregnancy when taken within 72 hours after unprotected sex or when birth control fails.

Levonorgestrel is a progestin. Progestins are hormones used in many birth control pills. Although levonorgestrel and similar emergency contraception pills contain a higher dose of levonorgestrel than birth control pills, they work in a similar way to prevent pregnancy, mainly by stopping the release of an egg from the ovary. Additionally, levonorgestrel also may prevent fertilization of an egg (the uniting of the sperm with the egg) or prevent the attachment (implantation) of a fertilized egg to the uterus (womb).

Emergency contraception pills do not work in women who are already pregnant and should not be taken during pregnancy. The FDA approved levonorgestrel in July 1999.

PRESCRIBED FOR: Emergency contraception pills are used to help prevent pregnancy after unprotected sex or when birth control methods fail. Emergency contraception is a backup method of preventing pregnancy and should not be used routinely.


  • Severe abdominal pain may be a sign of ectopic (outside of the uterus) pregnancy which requires immediate medical attention.
  • Levonorgestrel is not effective in terminating an existing pregnancy.
  • Some women may experience changes in their period such as spotting or bleeding before their next period. If the period is more than a week late, females should get a pregnancy test and consult with her doctor.
  • Emergency contraception pills do not protect against the AIDS virus or other sexually transmitted diseases.
Medically Reviewed by a Doctor on 9/15/2015

Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Pill Finder Tool

Need help identifying pills and medications?
Use the pill identifier tool on RxList.

Back to Medications Index

Health Solutions From Our Sponsors