I agree with Outtolunch. My AS is also an opiate addict (heroin), and towards the end of his second week of in-patient rehab (the first time), he was intent on leaving AMA. Took several of us to convince him to stay until the end only a few days later. He told us the same thing your son is saying -- he's already heard everything, there's nothing new to learn, he knows it all already, he just wants to get out so he can start his recovery program. Except he never started his recovery program. He was using again within hours of being released from rehab. I made the mistake of allowing him to move back into our house after rehab. He should have gone into a 3/4 house (sober living environment), where there is regular drug testing, structure, meetings, etc. I tried to encourage him to pursue recovery, but that put us into an adversarial position, and the next thing I knew, my house was a veritable "drug house" again. I ended up throwing him out. He lived in his car for about a week, then checked himself into another in-patient rehab program ON HIS OWN. His attitude is totally different this time. He's embracing it rather than fighting it. He's still there, so I can't tell you whether things will be different when he gets out. I can tell you, though, that he will NOT be moving back into my house when the program is over this time around.
I have concluded that there is nothing I can do or say that will convince my AS to go into or stay in recovery. He will do it only if HE really wants to and when he is ready. We can essentially force our addicted loved ones into a rehab program - that's pretty much how it happened the first time with my AS - but if he doesn't really want recovery FOR HIMSELF, it won't stick. My son knows that I will not be a part of his life if he is using because it is simply too hard for me. I can't make his problem my problem any longer. But I will definitely be there for him if he is pursuing recovery.