Thanks for your concern about your son.
Xanax (Alprazolam) is a drug given in
anxiety and panic disorders, however this drug can be addictive, both psychologically and physically. As you say, your son is
smoking marijuana along with Xanax, and now
Vistaril. Marijuana is an illegal drug and has many side effects. It can lead to severe anxiety, which people who abuse marijuana colloquially call a "bad trip". If marijuana were harmless, it would not be illegal. Furthermore, I would like to point out that the psychological effects of marijuana cannot be predicted. Your son is probably using it as a tranquilizer. Vistaril (
hydroxyzine) is an anti anxiety drug.
I'd advise you to take your son to a
psychiatrist, and I'd rather that your son be treated with an antidepressant from the Prozac family (SSRI's), as these drugs are good treating anxiety problems.
I hope this helps.