Plan B

Emergency Contraception

Levonorgestrel, marketed as Plan B® One-Step and Next Choice®, is classified as an “emergency contraceptive,” and is commonly referred to as “the morning after pill.” It is approximately a 50x dose of the progesterone-only oral birth control pill designed for daily use.

How It Works

The morning after pill has three effects:

  • Prevents ovulation, if it has not yet occurred.
  • Thickens cervical mucus, making it more difficult for sperm to enter the uterus.
  • Changes the lining of the uterus to prevent a baby from implanting and developing, should fertilization occur.1

Plan B labeling advises that the drug should be taken within 72 hours of intercourse, but the FDA indicates that it is effective until implantation, meaning that it will cause the destruction of a fertilized egg if one is present. There is no way to know before taking an emergency contraceptive whether fertilization has occurred or not.

Risks and Side Effects

Common side effects include:

  • Heavier menstrual bleeding
  • Nausea
  • Lower abdominal pain
  • Fatigue
  • Headache
  • Dizziness
  • Breast tenderness
  • Delay of menses by more than one week

Levonorgestrel is classified as “possibly carcinogenic to humans.” It has been shown to increase risk of cancer in animals.2

If you’re concerned that you may be pregnant or would like to discuss your options with a nurse, please contact us or schedule an appointment online.


  1. American Society of Health System Pharmacists (2014). AHFS Drug Information: Levonorgestrel. National Institutes of Health. Retrieved from http://www.nlm.nih.gov/medlineplus/druginfo/meds/a610021.html 

  2. [IARC (1999). Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT, p. V72 385. (Multivolume work). Retrieved from http://monographs.iarc.fr/index.php