Can you tell me what are signs of meth use or signs of a serious mental dissorder?

Many signs: People abusing any long-term stimulant develop anxiety, insomnia, irritability, paranoia and sometimes outright psychosis, as well as weight loss, severe skin and dental problems, and all the problems associated either with shooting it (aids, hepatitis b/c, endocarditis, other severe infections) or smoking ("crack lung"). Some look like severe schizophrenics after only a year or two of use.