how long does it take to get phentermine out of your system for a drug test
Re: How long for phentermine to get out of your system?? It takes 5 half lives for a drug to get completely out of your system. Phentermine has a half life of between 16-31 hours, so it would take anywhere from 80-155 hours (3.5 to 7 days) to be completely free of it.'ve been a phentermine fan for a long time and I'm aware of it losing its intensity over a few weeks. My question is how long does it usually take to get it out of your system before you can 'start over', if that makes sense?