how long does adipex last
9 Jun 2011. Adipex (phentermine) has a half life of approximately 25 hours. It takes 5.5 half life's for the medicine to be totally eliminated. Therefore Adipex will be in your system for approximately 137.5 hours (5.5 x 25) i.e.5.7 days (or 6 days). Votes: +0.