I have a daughter who used to substance abuse. I can tell you that legally you can't do anything at 13 in some states, let alone 17. I'm not sure why, but they make all the decisions. I would recommend a new evaluation of what his problems may be (aside from substance abuse) if he were younger or if he wasn't using drugs, but that won't help you much now that he is. Any diagnosis or new medication for a psychiatric illness won't really work if he is using illegal drugs/alcohol. As hard as it was for us, we finally made our daughter leave home at 18 because she would not get help and was getting worse in our house (and the younger kids were scared when the cops would stop by). Our gamble worked out and she quit--she is 24 now and has been clean since 19. I truly believe that it has to be their own decision by age 17 if they want to quit. Nothing can force them to do it, and you kind of have to learn to detach. I think you may get more out of posting in either "Teens and Substance Abuse" or "Parent Emiterus." Those are for parents of older kids who have been through similar problems. Most on this particular forum have younger kids. It is hard to relate to the incredible difficulties you have trying to get a 17 year old to help himself until you get there...it is frustrating. I used to stay up nights on end and just cry.
My daughter threatened suicide too--that is common when one is using drugs--and you don't really know what drugs he is using and how much. They don't tell us. They usually try to make us think it's just pot. It usually isn't just pot, although that's the Gateway drug. Pot and alcohol started when my daughter was 12 (no, I didn't have a clue). She progressed. My daughter started crushing ADHD stimulants into a pillcrusher and snorting them, then adding stuff with the stimulants. ADHD drugs are "hot" for teen abuse. It shocked me. Who thinks of crushing pills and snorting them? She claims she was addicted to speed.
Also, a psychiatric hospital, after daughter pulled a knife on herself, was so pointless. It didn't help her at all. In the end, she stopped using because she saw somebody with track marks up her arms and decided she didn't want to be that person. She didn't go to rehab--she just quit. We moved her from one state to another so that she could get away from her friends. She claimed that they harassed her each time she tried to quit. Once she had her own space, it was easier for her to stop. She even quit cigarettes.
I suggest learning how to detach or you'll drive yourself nuts. You can not stop your son at his age. He has to make that choice himself. Scary, I know. I"ve been there. I also suggest joining an organization such as Nar-Anon, so that you can have a lot of support from others who have a loved one who is using drugs. I found that really helpful.
Welcome to the board. Sorry though that you had to come here.