How often does he do it? If it's only like once or twice a year, let it slide. If it's once or twice a day, talk to him about it. Really, the best advice I can give you is to confront him. Tell him that, as a friend, he needs to stop. If that doesn't work, and you really think he should stop, tell his parents.
Best comment in this whole damn topic.
it's like once a day but he comes into school tripping and really high. So i'm like, dude go sleep it off in the nurses office but he's like shut up.
If i tell his parents they'll disown him...