Here are my thoughts

First, I think that you definitely want to say something to him - but I agree with keeping it as non-confrontational as possible.

Second, keep in your head the possibility that you have simply lost this friend. I am very fortunate to have two very close friends who I have been friends with for a long time - but most of my other high school friends have falled by the wayside. It happens - we all take our own paths through life and make our own decisions and sometimes you just have to let go.

Third - if you really want to help him, do not go into it with a superior attitude. Do not tell him what to do. Try and keep the conversation as light as possible.

Fourth - expect his reaction to be negative. And when I say "expect" I mean that it is a virtual certainty that he will be defensive and tell you to f*ck off and leave him alone or something like that. What you need to do in this case is not take that to heart. Let it slide off you. This is a standard defense mechanism for people who are being told that there is something wrong with how they are living their lives. We all want to believe that we know what we are doing and will often reinforce this with rationalizations.

I would recommend you start with something like

"I want to talk to you about something. I don't want to tell you how to live your life or anything like that, I am just concerned about you and, as your friend, I can't just let you go on doing this and not say anything about it. Feel free to take or leave what I have to say."