How to get a friend to stop screwing his life up?

Ive got this friend that Ive known for like a couple years and we used to skate and **** but now hes all getting into drugs and does coke and shrooms and smokes at least like twice a day. He also got kicked out of his pad and I just feel bad for him. I know hes deppressed and he is living at his friends house and is about to get sent away. He dosnt really go to school and theres alot of people that are out to get him cuz hez hella scandalous and steals from people. I barely ever see him anymore. I know its his deal and there alot more goin on than i know about but like its frustrating to see him all messed up like this. What would you say to someone in this condition?