Could a girls period be late if she took plan b?

Plan B effects: When a woman uses Plan B, additional hormones are introduced into her system. This can interfere with her normal menstrual cycle for a period of time.

Yes it could. : Plan B or any other hormonal drugs (like birth control) can alter menstrual bleeding. Something to keep in mind - not to worry you, but to be thorough - is that it *is* possible the “late” bleeding could indicate pregnancy and that Plan B was ineffective (there’s a small chance of Plan B failure). This should be considered particularly if menstruation is delayed 7 days greater than expected.