The Psychotomimetic States Inventory (PSI): Measuring psychotic-type experiences from ketamine and cannabis

Background: This study reports a new measure of psychotomimetic states in the context of cannabis and ketamine use. The Psychotomimetic States Inventory (PSI) has sub-scales of Delusory Thinking, Perceptual Distortions, Cognitive Disorganization, Anhedonia, Mania and Paranoia. Methods: The PSI was administered in two independent group, repeated measures designs: an experimental study of ketamine and a naturalistic study of cannabis. Results: Both cannabis and ketamine produced reliable increases in ratings of psychotomimetic state effects across several subscales. Conclusions: The PSI is a potentially useful measure of the nature and extent of the phenomenological effects of psychotropic drugs in schizophrenia-related research. (C) 2008 Elsevier B.V. All rights reserved.