Contradictory cognitive capacities among substance-abusing patients with schizophrenia: A meta-analysis Stéphane Potvin a,b , Christian C. Joyal a,c,d, ⁎ , Julie Pelletier e , Emmanuel Stip a,e a Fernand-Seguin Research Center, University of Montreal, Montreal, Canada b Department of Neurosurgery, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada c Philippe-Pinel Institute of Montreal, Canada d Department of Psychology, University of Quebec at Trois-Rivieres, Trois-Rivieres, Canada e Louis-H Lafontaine Hospital, Department of Psychiatry, Faculty of Medicine, University of Montreal, Montreal, Canada Received 1 December 2006; received in revised form 20 April 2007; accepted 24 April 2007 Available online 5 July 2007 Abstract Although a substance use disorder (SUD) is traditionally associated with psycho–bio-social impairments, recent investigations among persons with schizophrenia (Sz) generated divergent results. Certain persons with Sz + SUD might in fact present better social and cognitive functioning than persons with Sz without SUD. This meta-analysis was conducted to verify this counterintuitive possibility and to determine whether factors such as substance type, severity or nature of psychotic symptoms and age of the patients help discriminate these subgroups. Twenty-three studies met the inclusion criteria and data from 1807 persons with schizophrenia, with or without comorbid SUD, were available for analyses. As a group, persons with Sz + SUD did not obtain significantly higher scores at a Global Cognitive Index than persons with Sz without SUD, although they were better at the Trail Making Task and the speed processing domain. Secondary analyses showed the importance of considering intermediate factors, particularly the preferred substance used and the mean age. While consumption of alcohol was associated with a global cognitive scores similar to that of persons with Sz without an SUD and lower working memory capacities, preferential use of cannabis was instead associated with higher scores for problem solving and reasoning and visual memory. Age was inversely related to the size of the effects. It is concluded that previous mixed results obtained with cognitive evaluations of persons with Sz + SUD might reflect the heterogeneity of participants and that subgroups of patients might be defined on the basis of intermediate factors. © 2007 Elsevier B.V. All rights reserved. Keywords: Schizophrenia; Substance abuse; Cognition; Neuropsychology; Meta-analysis 1. Introduction Lifetime prevalence of substance use disorders (SUD) among persons with schizophrenia (Sz) approaches 50% (Kavanagh et al., 2002; Regier et al., 1990). Substance use and abuse are commonly reported as a mean to alleviate distress and painful affect by the patients (e.g. Dixon et al., 1990), and negative-type symptoms such as blunted af- fect, dysphoria, social isolation, and poor interpersonal skills represent risk factors for an SUD within this population (see Mueser et al., 1998 for an overview). These factors are associated with lower level of general functioning, less years of education, more neurological Available online at www.sciencedirect.com Schizophrenia Research 100 (2008) 242 – 251 www.elsevier.com/locate/schres ⁎ Corresponding author. University of Quebec at Trois-Rivieres, Department of Psychology, 3351 des Forges, C.P. 500, Trois-Rivieres, Quebec, Canada G9A 5H7. Fax: +1 819 376 5210. E-mail address: christian.joyal@uqtr.ca (C.C. Joyal). 0920-9964/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.schres.2007.04.022