What are Plan B side effects?
Last updated September 3, 2026.
Plan B's common side effects are nausea, vomiting, headache, dizziness, tiredness, breast tenderness, and lower belly pain, plus a next period that may come early, late, heavier, or lighter. Most resolve within a day or two. Three situations need action. Vomiting within 2 hours of the dose means the pill likely did not absorb, so retake it. A period missing after 3 weeks means take a pregnancy test. And severe lower abdominal pain 3 to 5 weeks after taking levonorgestrel is the one true red flag, since it can indicate an ectopic pregnancy; that needs urgent care. Menstrual changes are the most lingering effect: your cycle should normalize the following month. Taking Plan B repeatedly is not known to be dangerous, but it reliably scrambles cycle timing, which is a practical reason to set up a regular method rather than leaning on emergency contraception.
What to do
- Vomited within 2 hours? Take another dose; the first one likely did not absorb.
- Expect a weird period: early, late, heavier, lighter, or spotting between periods are all normal once.
- Test at 3 weeks: no period by then means pregnancy test.
- Know the red flag: severe lower abdominal pain 3 to 5 weeks later is an emergency.
- Repeat use scrambles cycles: a regular method is the better long-term answer.
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