I really hate to have to say this as so many people on this board hope for their child to be arrested so they will be safe, but as a 24 year veteran of Department of Corrections I can assure you that our prisons are a far cry from safe. I currently work at a minimum security prison and so far this year we've had a murder, multiple assaults, and God only knows how many fights. Drugs are rampant here. Granted, things like heroin are harder to get and more expensive but they are still available. There are times I feel that K2 is more common that tobacco.
That being said, I'm not trying to scare you. I just want you to understand that there are dangers here. That being said, there is also help to be had. We have drug treatment programs, anger management programs, mental health programs, and many others. Offenders simply need to take advantage of them and get the help they need. Unfortunately, as you have found out, more often than not they don't want the help. He has to want the help. Even if they force him into programs, and this happens regularly, he wont get much out of it unless he listens.
Your son seems to be very similar to mine and Lil's son. The only real difference that I can see is the IQ. Our son is very intelligent, sometimes too smart for his own good. Our son has never been diagnosed but we are positive that he is high functioning Aspergers. We know he is fond of marijuana, going on rants from time to time about how its ok that he uses it because it SHOULD be legal. We also know he has used synthetic marijuana although I don't think he has done this for a while. He also likes to drink which can sometimes be the most concerning issue since his bio-dad was an alcoholic. I don't know that he's done anything harder that what I've listed, but wouldn't be surprised to find out that he had done so.
The point is, at almost 21, our son is FINALLY starting to get a clue. He's held his current job since November and is slowly getting more hours. He has an apartment with his girlfriend. Granted, he promptly started making arrangements for his druggie friend to move in, but as the friend is still unemployed almost two months later HOPEFULLY he will figure out that he isn't really a friend and kick him out. He's almost paying his bills. Long story, will probably start my own thread on that if Lil decides to pay his past due electric bill for him. But he is trying. Not as hard as he should, not as smart as he should, but he IS trying. Hopefully your son will start to grow up as well. As truly hard as it is to do, sometimes you need to step back and let them fall then let them pick themselves up again. Its how people learn. I wish I could tell you the magic formula that would make your son turn his life around but unfortunately, that formula doesn't exist. Good luck and keep posting.