Gosh I hate to say it, but it could be meth too (or both).
Meth destroys your skin, teeth (pretty fast). In my opinion worse than heroin. But of course, both are awful and destroy you. With meth, mood swings are common.... you can snort it, shoot it, smoke it... You'll lose weight fast. He'd stay up for day on it potentially and then crash. People can be prone to psychotic rages when they abuse for a while.
I wish I knew the law more. I mean, I think you can only forcefully hold (called a 5150) in a psych ward( they'd evaluate him there all the way) if you believe him to be a harm to himself (suicidal, self harm maybe )... But I don't know how you prove that. Perhaps call your local hospital? I think they can only hold him 48 hours (again, I'm not sure) but if he was on drugs, you could at least then try to get him to rehab. Or at least he'd know you knew... (please remember I'm no expert. These are just ideas, thoughts...you'd have to check my suggestions for the full facts...)
If you knew he had drugs at his home, you could call the cops. Although, I don't know that all judges would say, give him rehab ...some would just jail him, which isn't what u are looking for.
What about staging an intervention? Can your family do that? Can you reach out to a rehab facility or someone local that does interventions and tell them your story? Get their advice? Maybe that's worth a try.
I wish I had more solid advice for you. Please keep us posted!
I'm sending you good vibes. You are doing the right thing...trying to help. In that way, you are being a good parent to him. This is a hard thing to help.
Thinking of you,