Perhaps the solution for the second group is to figure out a way to make them not get on drugs in the first place, at least not the variety that is prone to inducing psychosis. From what I know, most people who get hard into the drugs have usually had a shit start to their life. So better mental health care is probably a good option to start with. Besides that, better systems for looking after kids in care, more resources being put into rehabilitating parents who are in/have been in prison, more of an emphasis on family preservation and/or reunification are good bets.

I do think that the second group are fixable and can become their former selves again, but it's a fine line. The only option I see for them is some sort of forced intervention and rehabilitation. But obviously you can't just take people in psychosis, stick them in a prison, and wish for the best. You also can't just make them go cold turkey, so you'd need somewhere to ethically hold them (more than likely against their will), while also still providing some of whatever drug they're on, without risking an overdose or allowing any secret syphoning into other people's bodies (people pretending to shoot up but saving some to sell to other people, etc), and all of that while keeping them and their families reasonably happy, and not violating UN conventions on illegal detainment, and our human rights laws. So thats probably not happening under any democratic government

And then you'd also need a way to make sure that it isn't easily accessible to them again. Which probably means even more enforcement of drug laws, more drug dogs in public, random searches, etc, which would also piss off everybody

Tbh I don't see how it is possible to rehabilitate them in an ethical, just, and civilised way. But nonetheless, there are options. It's the sort of thing I could see working in a dictatorship, but then the problem becomes the dictators or their cronies getting paid off to look the other way