Fuck man, I'm way too familiar with the OP's situation.
Some background: One of my best friends was/is into it deep. He could be clean now, but who knows. We grew up together, attended preschool throughout highschool, lived one block away from me. We were roommates during my last two years at OSU, he worked odd jobs, distro center stuff. It was college, so of course we were partying, he was always the "look at me" kind of guy, "I'm doing something other than drinking." He casually starts popping pain pills for fun. Didn't think much of it, then it got more frequent, then he's crushing them up in a mortar and pestle on a random Monday evening. He gets more and more out there, starts to slide at work, pills increase, gets fired from several jobs, moves back to our hometown in the Ohio Valley.
Then shit really started to go downhill, shacked up with another addict girl (has two kids, taken from her by child services), taking every pill he could get his hands on. Morphine patches, oxycontin, stealing from his parents, her parents, wrecks two cars, DUI, real degenerate stuff. After all that he ends up driving again, falls asleep at the wheel, fractures his neck and severely injures someone from the other car. I think he had to get a leg amputated. He's then in the hospital and back on the meds.
The last time I saw him was last summer and he was not all there, just out in space when talking. It really sucked seeing him still in that state. We all tried to help him, friends and family, multiple intervention style confrontations. None of it really worked. He never owned up to shit, always someone or something else causing his problems, everyone against him and blah blah. His parents are well aware of everything and they have money, so I'm not sure why he never went to a proper rehab facility.
I wish him well and I hope he gets his shit together, but as of now I've pretty much cut him off. He's back living with is parents, and the last I heard he was "doing better." But I've heard that regularly for the last 5 years. For reference, the bad stage began around 2009 and he's still struggling.
You can only do so much. Just support them as best you see fit, and at the end of the day change has to come from within.