Hi hun, Yes I have been on them. Fentenyl. I was on the lowest dose of 25mg. It could take up to 12 hours to begin to work. You are wise to get the right tape. I ruined 3 in one day. I found them laying on the floor around my house. Fortunately there were no kids around. You have to be careful with them. You can wear them when you bathe. Each one is good for 72 hours. Make sure you wash your hands after putting them on. I didn't get much out of them myself. But other people swear by them. Maybe it's because the dose was so low. Never wear more then one at a time. If I had to rate how I liked them I would give it about a 3 out of 10.