No! No! No!
I beg of you, do not listen to any of these people. Your problem is that your having difficulties getting along with your son, who also has problems of his own. Everyone here is telling you that you should let him go to fend for himself. Tell me this, do you want to push your son out of your life because he's not minding you, or do you want to help him fix his problems so you can breath easy that he's on a better path?
Hear me out. If you love your son, you will do everything in your power to help him, not disown him. I'm not a psychologist, so the advice I'm about to give may very well not work, but I can tell you that everyone else here is giving the worst possible advice. DON'T DISOWN YOUR SON.
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First things first, you need to figure out why you and your son aren't getting along. Obviously the drugs and alcohol are adding onto the stress, but I'm willing to bet there are other underlying problems.
You said your son told his brother that he doesn't need you at all. Talk to the brother and see if you can learn anything else about your son and what else might have him upset. Think about some of the arguments you have had and ask yourself how they were started.
It's probably safe to assume that your son might be depressed. Often, parents who try to help their children by scolding them will often discourage their children from taking up more responsibilities. At the age of 21, he may feel like you're treating him too much like a child. I don't know what the problem is, but consider the possibility that your efforts to help him may have come off the wrong way to him.
He could be ashamed of his lifestyle, and when you tell him he needs to get a job, you make him feel worse. Maybe he feels like there are other issues in his life he wants to fix and he feels like you're only getting in the way.
Whether your son lives in the same house as you, or not, you MUST work with him. Do NOT disown him. Do NOT let him hit rock bottom and hope he is able to pick himself back up. Everyone else here believes you should let him suffer for his own actions, but he's your son. Children aren't supposed to work for their parents, parents are supposed to work for their children.
Please, don't give up on him. Talk to him like an adult, but try to sympathize with him like he's a child who needs their parent. You don't have to give into his every whim. Before you can fix his alcoholism problem, or his drug problem, you need to fix your relationship with him. This might mean you have to let him think he's right when he's not. When the two of you are on good terms, it's then you can talk to him about his problems (but don't badger him about them, try to be understanding).
