How long does plan b stay in your system?

5 days: "plan b" can stay in your system for up to five days, though it is not effective after three days max. If you have taken it, anticipate an irregular period afterwards. This is typical.

24-48 hours: The drug reaches its highest concentration in about 2 hours and, assuming normal liver and kidney function should be out of your body between 24 and 48 hours.

Briefly: Even though Plan B is out of your system relatively quickly, the hormonal changes that occur may take up to several months after the Plan B was taken to even out.