Toward the very end of my dad's pancreatic cancer battle, he was having a lot of problems with pain. He was already taking Oxycontin time-release pills three times a day plus Percocet for breakthrough pain, but toward the end, he was having a lot of pain despite the medication prescribed. So his doctor suggested a Fentanyl patch. Although it was supposed to be good for three days, we found that after 48 hours it was losing its effectiveness and were given permission to change it every two days instead of every three days. It is hard to say whether this gave any relief or not, since he was on other powerful pain meds at the same time. Thankfully the only side effect from any of this stuff was constipation. He did not experience hallucinations or other mind-altering experiences, and was coherent until the very end. The patch went on easily, although he was pretty much skin and bones at the end of his illness.
