1. ¹Department of Psychiatry, The University of Chicago, Chicago, IL, USA
2. ²The American Institute for Cognitive Therapy, New York, NY, USA
3. ³University of New York at Buffalo, Behavioral Medicine, New York, USA

Correspondence: Dr H de Wit, Department of Psychiatry, MC3077, The University of Chicago, 5841 S. Maryland Avenue, Chicago, IL 60637, USA. Tel: +1 773 702 1537; Fax: +1 773 834 7698; E-mail: hdew@midway.uchicago.edu

Received 29 July 2002; Revised 3 December 2002; Accepted 27 January 2003; Published online 30 April 2003.

Abstract

This study investigated the acute effects of ⁹-tetrahydrocannabinol (THC) on four behavioral measures of impulsivity in recreational marijuana users. Although impulsive behavior has been studied using several different measures of impulsivity, few studies have utilized more than one of these measures on a single cohort. In this study, 37 healthy men and women participated in three sessions, in which they received capsules containing placebo, 7.5, or 15 mg THC in randomized order under double-blind conditions. Subjects were tested on the following four tasks: the Stop task, which measures the ability to inhibit a prepotent motor response; a Go/no-go task; a Delay discounting task, which measures the value of delayed or uncertain reinforcers; and a time estimation task, which measures alterations in time perception through a time reproduction procedure. Subjects also completed mood questionnaires and general measures of performance. THC produced its expected effects on subjective measures including increases in ARCI euphoria and marijuana scales. THC increased impulsive responding on the Stop task but did not affect performance on either the Go/no-go or Delay or Probability discounting tasks. On the time reproduction task, THC increased estimates of the duration of short intervals while not affecting estimates of longer intervals. There were no significant correlations between the four tasks either before or after drug administration. These results suggest that THC may increase certain forms of impulsive behavior while not affecting other impulsive behaviors. The dissociations between the four measures of impulsivity suggest that impulsivity is an assemblage of distinct components rather than a unitary process.