I have been on Fentanyl (25, then 50 then 75) patches for about 18 months now. Problem is that they don't seem to be working very well any more. Does the body build up a resistance? I am getting more side effects but less pain relief. I am using this (and other medication) to stop the agonizing pain from a broken back and severed nerves. If these are stopping working - I truly don't know how to go on - the pain is simply too great to bear most days. Any ideas anyone?