My buddy was hooked on fentanyl patches, he actually ODed and stopped for a while, then he started to do it again, mixed it with crack but he was super functional about it. He was going to school for a masters in social work, along with counseling licenses. I didn't know about it before he ODed, then when I found out he was doing it again, I confronted him about it and he told me about how much he couldn't kick it. He said that it hurt too much even after he ODed. My wife and I alternated days and took a week and a half off of work and put him on our couch and just took care of him. It was ugly and it came in waves that were sometimes extremely fast. We took his keys and his phone too. It took a week before the pain went away and another few days before the nausea went away and after that he was just really weak for another 2 weeks. He went back home and we had his roommate clean his room before he did and he has been off since.
They have to want it though.