Psychedelic Effects of Ketamine in Healthy Volunteers
Anesthesiology – January 01, 1998
Source: CrossRef
Summary
Even low doses of ketamine can reliably induce profound psychedelic experiences in healthy individuals. Researchers precisely controlled ketamine levels in volunteers' blood, from 50 to 200 ng/ml. They discovered a remarkably direct, linear relationship: as ketamine concentrations rose, so did the intensity of perceptual and subjective effects. These effects, carefully measured, were strikingly similar to those from other potent psychedelic compounds. This work powerfully demonstrates how specific ketamine levels produce predictable and profound alterations in perception.
Abstract
Background Ketamine has been associated with a unique spectrum of subjective "psychedelic" effects in patients emerging from anesthesia. This study quantified these effects of ketamine and related them to steady-state plasma concentrations. Methods Ketamine or saline was administered in a single-blinded crossover protocol to 10 psychiatrically healthy volunteers using computer-assisted continuous infusion. A stepwise series of target plasma concentrations, 0, 50, 100, 150, and 200 ng/ml were maintained for 30 min each. After 20 min at each step, the volunteers completed a visual analog (VAS) rating of 13 symptom scales. Peripheral venous plasma ketamine concentrations were determined after 28 min at each step. One hour after discontinuation of the infusion, a psychological inventory, the hallucinogen rating scale, was completed. Results The relation of mean ketamine plasma concentrations to the target concentrations was highly linear, with a correlation coefficient of R = 0.997 (P = 0.0027). Ketamine produced dose-related psychedelic effects. The relation between steady-state ketamine plasma concentration and VAS scores was highly linear for all VAS items, with linear regression coefficients ranging from R = 0.93 to 0.99 (P < 0.024 to P < 0.0005). Hallucinogen rating scale scores were similar to those found in a previous study with psychedelic doses of N,N-dimethyltryptamine, an illicit LSD-25-like drug. Conclusions Subanesthetic doses of ketamine produce psychedelic effects in healthy volunteers. The relation between steady-state venous plasma ketamine concentrations and effects is highly linear between 50 and 200 ng/ml.