How Plan B works
Plan B contains levonorgestrel. According to the U.S. Food and Drug Administration, it usually stops or delays the release of an egg from the ovary. Current evidence does not support an effect on implantation, and Plan B will not work if a pregnancy already exists.
Plan B is different from mifepristone and misoprostol, the medications used for medication abortion.
When to take it
Follow the package directions and take levonorgestrel emergency contraception as soon as possible within 72 hours after unprotected sex or birth control failure. The sooner it is taken, the better it is expected to work.
Other emergency contraception options have different time windows. A pharmacist or licensed health professional can explain which options may still be available if more than 72 hours have passed, if you take medicines that can interact, or if you have questions about effectiveness.
Possible side effects and period changes
Possible effects include nausea, lower abdominal discomfort, tiredness, headache, dizziness, breast tenderness, and bleeding or spotting. Your next period may come earlier or later and may be lighter or heavier than usual.
Severe abdominal pain needs prompt medical attention because it can be a sign of an ectopic pregnancy or another urgent problem.
When to take a pregnancy test
Take a pregnancy test if your period is more than one week late, or follow the timing recommended by a health professional. A test taken too early can be negative even when pregnancy is present, so repeat testing may be needed.
Care Net offers pregnancy testing at no cost. Call before visiting to confirm current hours and availability.
Information on this page is general education, not medical or legal advice. Talk with an appropriately licensed professional about your situation.
Sources and review
Where this information comes from
Independent sources support the medical, legal, and community information on this page. Care Net's service details are maintained as current first-party information.
- Plan B One-Step informationU.S. Food and Drug Administration · Independent source
- Emergency contraceptionAmerican College of Obstetricians and Gynecologists · Independent source
- Ectopic pregnancyAmerican College of Obstetricians and Gynecologists · Independent source
- Pregnancy testsU.S. Food and Drug Administration · Independent source
Sources last reviewed .