Plan B emergency contraception should not be used as a regular method of birth control. However, if you have already used Plan B, it can be safely used again after another instance of unprotected sex or birth control failure. It works in the same way every time you take it and will not become less effective over time.
Plan B doesn’t provide long‑term protection against future pregnancy—it works to help prevent pregnancy after only one act of unprotected sex or birth control failure. It will not affect your future fertility.