What is the prognosis of a 20yr old male with substance abuse pyscosis. He was using dmt and mephadrone? Please any information would be helpful!

Depends. In general the psychosis resulting from most substance use resolves itself after the substance is out of the person's system. However, chronic use of certain substances, especially in individuals who may have a genetic risk for psychosis or bipolar disorder, can lead to chronic symptoms of psychosis. This is particularly true of methamphetamine and possibly marijuana.
Good once off it. Substance abuse is a chronic and complicated problem that involves multiple layers of treatment, including therapy, psychiatric and medical help, acute detox and long term sport from family, friends and loved ones and often from na meetings. Once someone has gone through the detox period, the psychosis itself often resolves completely, and then the hard work begins...