coma can result. These substances are most commonly smoked or taken orally, but they
may also be snorted or injected. Although the primary psychoactive ef fects of PCP last for
a few hours, the total elimination rate of this  drug from the body typically extends 8 days
or longer. The hallucinogenic effects in vulne rable individuals may last for weeks and may
precipitate a persistent psychotic episode resembling schizophrenia. Ketamine has been
observed to have utility in the treatment of  major depressive disorder. Withdrawal symp-