Mackey's right. This problem is way too big for you to handle on your own. The good news is that your friend is willing to talk about it, but the most important thing for a drug addict after professional counseling is a network of friends who will get him away from the environments where he used to use drugs. Environment plays a very powerful role in addiction. Next is to get him away from friends who encourage him to use and help him to make better connections with friends who don't use, even if that means making new friends. It's going to be a painful process, and you can't give up on him if he falls off the wagon. Just be supportive and don't judge. Judging is one of many things that keep people addicted.

Whew! That was a mouthful.