My family has a long history of schizophrenia, been one or two per generation for 5 generations, including my younger brother. Most serious mental illness is a biochemical issue and the anti-psychotics address the symptoms not the cause. And the self-medicating with recreational drugs is the same.
He was treated with IV B vitamins in the 70’s (as a teen) and made a complete recovery in about 6 months of weekly infusions. The difference was apparent immediately after the first infusion. He remains very careful about food (no sugar, lots of B vitamins) and has been a successful productive adult. It was a controversial treatment at the time and I don’t think it has ever become widely accepted but it worked for him and if any of my kids presented with mental illness it is the first thing I would do.
Nowadays, there are quite a few clinics doing IV therapy for anti-aging, sports medicine, drug rehab, etc. There are even mobile services that do them in home. Prices vary wildly, from $200 to $2000, so shop around.
It’s late in the game for your nephew, but it can’t hurt and it might help. That’s my two cents, fwiw.
Do you happen to know if that B vitamin treatment was performed successfully for other mental illnesses, such as anxiety, depression or OCD?