(((JSK))))
What you describe with your friend is very similar to the path my son chose. He too started with the painkillers, and moved on to heroin because it was "cheaper" to maintain.
There is a lot of information up top called "stickies" that's good place to start, to learn more about addiction.
Unfortunately, there's not much "you" can do to stop your friend. He has to want to stop. When he's ready, there's a lot of help out there for him.
As far as telling his parents...I would want to know. But I will warn you that someone did try to warn me, and I shrugged it off as gossip.
Stick around, read around, there are many good people on these boards.
(((Hugs)))
Cece