I have been on the Fentanyl patch going on three months now. When I put my first patch on June 6th at 7:00 am I started feeling it work by lunch time. On the third day I thought I was getting a virus, I had cold chills and didn't feel well at all so I went home and went to bed. The next morning I put on my second patch and on day three I felt the same way so I called the doctor and he said it may not have had enough time to build up in your system so by the end of the first month I counted ten bad day's I had. When I went back to him I told him that and he said I was having withdrawls so he wrote me a script to change them every 48 hrs and I have done great since then. My question is has anyone else had this problem because every thing I have read it say's they are supposed to last 72 hrs but the last 24 feels like I was running on fumes. The patch was the Mylan brand.