How long can prednisone be in your system?

Depends! Prednisone has a pre conversion half life off one hour. Prednisone is a converted into prednisolone, which also has "steroid" effects! Its plasma half life as Prednisolone is 2-3 hours. So the total effect a duration of 18-36 hours. But once its out of your system it takes a while for your system to re-regulate itself as well.