Phencyclidine (PCP) was originally developed as an intra¬ venous surgical anesthetic in the 1950s. It was used routinely in veterinary medicine, but clinical trials with humans were discontinued in 1965 due to a number of adverse side effects, including agitation, delirium, and irrational behavior (National Institute on Drug Abuse, 2001b). It is classified as a dissociative anesthetic because users experience a trancelike, out-of-body feeling as well as a detachment from their environment (National Institute on Drug Abuse, 2001a).