1. ¹Department of Psychiatry, School of Clinical Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
2. ²Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, UK
3. ³Department of Experimental Psychology, University of Cambridge, Cambridge, UK
4. ⁴Brookfields Hospital, Cambridge Drug & Alcohol Service, Cambridge, UK

Correspondence: Professor BJ Sahakian, Department of Psychiatry, School of Clinical Medicine, University of Cambridge, Box 189, Addenbrooke's Hospital, Cambridge, Cambridgeshire CB2 2QQ, UK. Tel: +44 1223 331209; Fax: +44 1223 336968; E-mail: ke220@cam.ac.uk

Received 10 May 2005; Revised 1 August 2005; Accepted 2 August 2005; Published online 14 September 2005.

Abstract

Cognitive function was assessed in chronic drug users on neurocognitive measures of executive and memory function. Current amphetamine users were contrasted with current opiate users, and these two groups were compared with former users of these substances (abstinent for at least one year). Four groups of participants were recruited: amphetamine-dependent individuals, opiate-dependent individuals, former users of amphetamines, and/or opiates and healthy non-drug taking controls. Participants were administered the Tower of London (TOL) planning task and the 3D-IDED attentional set-shifting task to assess executive function, and Paired Associates Learning and Delayed Pattern Recognition Memory tasks to assess visual memory function. The three groups of substance users showed significant impairments on TOL planning, Pattern Recognition Memory and Paired Associates Learning. Current amphetamine users displayed a greater degree of impairment than current opiate users. Consistent with previous research showing that healthy men are performing better on visuo-spatial tests than women, our male controls remembered significantly more paired associates than their female counterparts. This relationship was reversed in drug users. While performance of female drug users was normal, male drug users showed significant impairment compared to both their female counterparts and male controls. There was no difference in performance between current and former drug users. Neither years of drug abuse nor years of drug abstinence were associated with performance. Chronic drug users display pronounced neuropsychological impairment in the domains of executive and memory function. Impairment persists after several years of drug abstinence and may reflect neuropathology in frontal and temporal cortices.