1. ¹Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
2. ²GW Pharmaceuticals Ltd, Salisbury, UK

Correspondence: Dr RD Rogers, Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford OX3 7JX, UK. Tel: +44 1865 226 399; Fax: +44 1865 793 101; E-mail: robert.rogers@psych.ox.ac.uk

Received 3 August 2005; Revised 30 May 2006; Accepted 7 June 2006; Published online 27 September 2006.

Abstract

Research suggests that risky decision-making is sensitive to neuromodulatory influences acting upon corticolimbic circuitry. However, while other evidence attests to effects of -9 tetrahydrocannabinol (THC) on the activity of reward pathways, relatively little is known about the possible involvement of cannabinoid activity in risky choice. In this experiment, we examined the effects of a single sublingual 5 mg dose of THC on a test of risky decision-making (requiring choices between simultaneously presented gambles differing in their magnitude of gains, magnitude of losses and the probability with which these outcomes were delivered). Tests of non-normative decision-making involving risk-aversion when deciding between gains and risk-seeking choices when deciding between losses were also included. In all, 15 healthy adults were administered 5 mg THC and placebo in a double-blind, placebo-controlled, within-subject, cross-over design. THC had three principal effects relative to placebo: (i) THC reduced choice of gambles with variable gains and losses, but increased choice of gambles with zero-expected value; (ii) THC reduced participants' attention towards losses when the probability of winning was low (and the probability of losing was high); and (iii) THC speeded participants' responses to gambles with large compared to small potential gains. These results suggest that THC mediates specific motivational processes and the processing of reinforcement cues during risky choice, perhaps reflecting altered CB₁ receptor or catecholamine activity within corticolimbic pathways.