... was cheating on me. we started having marriage troubles. My Dr. said it could be caused by me taking the phentermine. I then was takin off of it. I lost over 100lbs on it but have regained it all back cause of my depression. Does anyone know how common phychosis is from taking phentermine? It seems funny that everything seems to deal with my husband and he did confess 2 times but he took them both back. I have been on anti phychotic medication for over a year now. If anyone has any information about phycosis while being on phentermine please let me know