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Understanding Levonorgestrel: A Guide to Emergency Birth Control Options

Levonorgestrel 1.5 mg (ie. My Choice, Plan B)

The morning-after pill (levonorgestrel 1.5 mg) is a method of emergency birth control, used toprevent pregnancy for women who have had unprotected sex or whose birth control method has failed (for example, a broken condom or missed birth control pill). Note, this contraceptive isintended only for backup birth control, NOT as a primary method of long-term birth control. 

How does it work?

Morning after pills prevent pregnancy after unprotected sex bydelaying or preventing ovulation, which is the process by which an egg is released into the female reproductive system for potential fertilization by sperm and subsequent pregnancy. Note, this is NOT the same as other medications used for medical abortions, sincemorning after pills cannot terminate a fertilized egg that has already attached to the uterus and begun to develop. In other words, Plan B does not abort a pregnancy. 

How and when to best use the morning after pill?

Levonorgestrel (1.5 mg) is a pill taken by mouth and ismost effective when taken less than 72 hours after unprotected sex. You may know this medication by its common brand names like Plan B, My Choice, or EContra EZ, to name a few. For maximum effectiveness, emergency contraception should be taken as soon as possible after unprotected sex. You can take emergency contraceptive pills anytime during your menstrual cycle. 

If taken within 24 hours = risk of pregnancy is ~5%

If taken within 48 hours = risk of pregnancy is ~15%

If taken within 72 hours = risk of pregnancy is ~50%

ERGO…THE EARLIER taken after sex THE BETTER chances of preventing pregnancy.

If you vomit within two hours after taking the morning-after pill, please ask your health care provider if you should take another dose.

Don't have sex until you start another method of birth control.The morning-after pill doesn't offer lasting protection from pregnancy. If you have unprotected sex in the days and weeks after taking the morning-after pill, you are again at risk of becoming pregnant. Be sure to begin using or resume use of birth control.

Situations in which you may want to consider using this pill as emergency birth control may include:

  • Sex in which no birth control method was used (no condom, IUD, pill, hormonal implant)
  • Having sex after having missed a birth control pill
  • Sexual assault
  • The method of birth control failed during sex (ex. broken condom)

Risks ofLevonorgestrel

Emergency contraception is an effective option for preventing pregnancy after unprotected sex, but is not as effective as other methods of contraception.This medication is NOT intended as a long term method of birth control, and should only be used for emergencies (mentioned above).

Users should know:

  • The morning-after pill can fail even with correct use
    • This pill works bydelaying or preventing ovulation and egg implantation, but may not be as effective in preventing pregnancy if you have already ovulated (this depends on what day in your cycle you are on).This is why it is important to NOT USE emergency contraception as a long-term form of birth control.
  • Levonorgestrel is NOT an effective way to prevent sexually transmitted infections/diseases (STIs/STDs). To protect yourself against STIs/STDs, consider using other barrier methods, like condoms.

Do NOT useLevonorgestrel if you are:

  • allergic to any component of the morning-after pill
  • taking certain medications that can decrease the effectiveness of the morning-after pill, such as barbiturates or St. John's wort
  • Breast-feeding
  • Already pregnant

Side effects typically last a few days and might include: 

  • Nausea or vomiting
  • Dizziness
  • Fatigue
  • Headache
  • Breast tenderness
  • Bleeding between periods or heavier menstrual bleeding
    • If you experience bleeding/spotting that lasts longer than a week or develop severe lower abdominal pain 3-5 weeks after taking Levonorgestrel, contact your doctor. These symptoms can indicate a miscarriage or that a fertilized egg has implanted outside the uterus, usually in a fallopian tube (ectopic pregnancy).
  • Lower abdominal pain or cramps
  • Delayed period by up to 1 week
    • Note, if you don't get your period within 3-4 weeks of takingLevonorgestrel, you should take a pregnancy test.


Mayo Clinic Staff. "Morning-after pill (Emergency Contraception)."Mayo Clinic, Mayo

Foundation for Medical Education and Research, 2022,