You got strong nerves there, man. I for example couldn't deal with a drug addict, neither would I even let them near my house. It's just that I'm against drug use totally and I think those are very weak people.

But yeah, I guess it would be hard for me not to help a good friend who would have such a problem.

All you can do is talk to this guy and try get some sense in his head that using drugs is not the answer. Then take him to rehab. But the man needs to understand and want himself to get rid of the addiction. Otherwise it won't work.

One major thing is as the others said already, think first about yourself. If the man doesn't want to change it's his life. There's nothing you'll do about it. Even if you force him in rehab, he'll be out of it soon and will continue using.