Plan B One-Step: Seven Questions and Answers

What you need to know about Plan B One-Step, the emergency contraceptive.

Medically Reviewed by Carol DerSarkissian, MD on March 09, 2022

Here are questions and answers about the emergency contraceptive Plan B One-Step.

1. What is Plan B One-Step?

Plan B One-Step is an emergency contraceptive pill taken by mouth after unprotected sex. It is used to prevent pregnancy. It is not for routine contraceptive use and does not prevent against sexually transmitted diseases, including HIV.

2. How is Plan B One-Step taken?

Plan B One-Step should be taken within 72 hours of unprotected intercourse. When taken within 72 hours, it decreases the chance of getting pregnant by 89%.

It's even more effective when taken within 24 hours. Effectiveness decreases the longer a woman waits to take it.

3. Who may buy Plan B One-Step?

Plan B One-Step can be purchased over the counter by anyone. There's no need to have a prescription or show proof of age.

4. What is Plan B One-Step's active ingredient?

Each pill contains levonorgestrel, a synthetic version of the hormone progestin. Levonorgestrel has been used in birth control pills for over 35 years. Plan B One-Step contains a higher dose of levonorgestrel than that in regular birth control pills.

5. How does Plan B One-Step work?

Plan B One-Step works like other birth control pills to prevent pregnancy. The drug acts primarily by stopping the release of an egg from the ovary. It may prevent a sperm from fertilizing the egg.

If fertilization does occur, Plan B One-Step may prevent a fertilized egg from attaching to the womb. If a fertilized egg is implanted prior to taking Plan B One-Step, the drug will not work and pregnancy proceeds normally.

6. Does Plan B One-Step have any side effects?

Like any medication, Plan B One-Step does have side effects. The most common side effect is nausea, which occurs in about a quarter of women after taking the drug. Other side effects include abdominal pain, fatigue, headache, dizziness, vomiting, and menstrual changes. If you vomit within two hours of taking Plan B One-Step, consult a health care professional to find out if you need to take another dose.

7. Is Plan B One-Step the same as RU-486?

No. RU-486, sold as Mifeprex, is a prescription drug for medical abortion. Mifeprex is used after a woman is already pregnant. Plan B One-Step is an emergency contraceptive. It is used to prevent pregnancy. While some people do feel that pregnancy begins at the time of conception, many doctors and the FDA do not describe Plan B One-Step as an abortion pill but as emergency contraception.

Show Sources

SOURCES: News release, Barr Pharmaceuticals. FDA: "FDA's Decisions Regarding Plan B: Questions and Answers," May 7, 2004. Steven Galson, MD, MPH, director, FDA's Center for Drug Evaluation and Research. Teva Women's Health, Inc.

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