A single 0.5 mg dose of Xanax stays in your system for 3 to 5 days. But the longer period of taking Xanax, and the higher the dosages, the longer it will take your system to get rid of traces of Xanax.You may sometimes need a month or more to get yourself quite clear of the medication.hat is, after this length of time, one half of the taken dose is still present in your system. After another 6 to 12 hours, a half of this half is still present, and so on. How long Xanax will stay in your system cannot be predicted for sure.