Cannabis users have higher premorbid IQ than other patients with first onset psychosis Laura Ferraro a,b, ⁎, Manuela Russo a , Jennifer O'Connor a , Benjamin D.R. Wiffen a , Maria Aurora Falcone a,e , Lucia Sideli b , Poonam Gardner-Sood a , Simona Stilo a , Antonella Trotta a,c , Paola Dazzan a , Valeria Mondelli a , Heather Taylor a , Bess Friedman a , Hannah Sallis d , Caterina La Cascia b , Daniele La Barbera b , Anthony S. David a , Abraham Reichenberg a , Robin M. Murray a , Marta Di Forti a a Institute of Psychiatry, Department of Psychosis Studies and Biomedical Research Centre, King's College, de Crespigny Park, Denmark Hill, London SE5 8AF, United Kingdom b Sezione di Psichiatria del Dipartimento di Biomedicina Sperimentale e Neuroscienze Cliniche (BioNeC), Università di Palermo, Via “Gaetano La Loggia” 1, 90100 Palermo, Italy c Dipartimento di Scienze Pedagogiche e Psicologiche “G. Catalfamo”, Universita' degli studi di Messina, Via Concezione 8, 98100 Messina, Italy d Institute of Psychiatry, Department of Biostatistics, King's College, de Crespigny Park, Denmark Hill, London SE5 8AF, United Kingdom e Institute of Psychiatry, Department of Psychology, King's College, de Crespigny Park, Denmark Hill, London SE5 8AF, United Kingdom abstract article info Article history: Received 26 February 2013 Received in revised form 9 July 2013 Accepted 25 July 2013 Available online xxxx Keywords: Premorbid IQ Cannabis First Episode of Psychosis (FEP) Schizophrenia Cognition IQ Risk of psychosis Substance use Background: A number of studies have reported that patients with psychosis who use cannabis have better cog- nitive performance than those who do not. This is surprising as cannabis can impair cognition in healthy subjects. An obvious question is whether the better current performance of psychotic patients who have used cannabis is a reflection of their having a higher premorbid IQ than those psychotic patients who haven't used cannabis. Aim: In a sample of patients at their first episode of psychosis, we tested the hypothesis that patients who smoked cannabis would have a higher premorbid IQ than patients who did not. Methodology: 279 participants (119 patients and 160 healthy controls) were assessed in order to obtain current and premorbid IQ measures and detailed information on cannabis use. We examined the association between cannabis use and both premorbid and current IQ in patients and controls. Results: Patients who had ever smoked cannabis had significantly higher current (p b .001) and premorbid IQ (p = .004) compared to patients who had never used cannabis. This difference was not found among controls. Conclusions: These findings suggest that the better cognitive performance of patients with their first episode of psychosis who have used cannabis compared with those who haven't is due to the better premorbid IQ of the former. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Cognitive impairment is a key feature of schizophrenia (Mohamed et al., 1999; Zanelli et al., 2010; Matheson et al., 2011) and also occurs, though to a lesser extent, in affective psychosis (Krabbendam et al., 2005; Kravariti et al., 2009). However, not all psychotic patients show cognitive impairment (Kremen et al., 2000). A recent epidemiological study of first-admission patients with psychotic disorders estimated that as many as 16% of schizophrenic, 20% schizoaffective, 42% of bipo- lar, and 42% of depressed patients may not be cognitively impaired (Reichenberg et al., 2009). Cannabis use has been repeatedly shown to be a risk factor for the development of psychosis (Henquet et al., 2005; Moore et al., 2007; Potvin and Amar, 2008; Di Forti et al., 2009; Casadio et al., 2011). Three recent meta-analyses have reported that among patients with psychosis, those who have used cannabis show better cognitive perfor- mance than those who have not (Potvin et al., 2008; Yücel et al., 2010; Rabin et al., 2011). This is unexpected as it has been shown that canna- bis use can impair cognition in healthy subjects (Fried et al., 2005; Meier et al., 2012). Two different explanations have been advanced for this finding. The first suggests that those psychotic subjects who use cannabis have less premorbid cognitive impairment than those who do not. This could be because good premorbid functioning is necessary to acquire and sustain an illegal drug habit (Joyal et al., 2003; Stirling et al., 2005; Rodriguez- Sanchez et al., 2010) or because cannabis use increases the risk of psychosis in a subgroup of patients with less neurodevelopmental vul- nerability (Løberg and Hugdahl, 2009; Schnell et al., 2009; de la Serna et al., 2010; Yücel et al., 2010; Leeson et al., 2012; Schnell et al., 2012). To our knowledge, only one recent study (Leeson et al., 2012) has found higher premorbid IQ in patients who smoked cannabis – among 99 FEP subjects – using the Wechsler Test of Adult Reading (WTAR) as an estimated measure of premorbid IQ. Other studies (Jockers-Scherübl Schizophrenia Research xxx (2013) xxx–xxx ⁎ Corresponding author at: Sezione di Psichiatria del Dipartimento di Biomedicina Sperimentale e Neuroscienze Cliniche (BioNeC), Università di Palermo. Via “Gaetano La Loggia” 1, 90100 Palermo, Italy. Tel.: +39 3208904741. E-mail address: laura_ferraro@hotmail.it (L. Ferraro). SCHRES-05534; No of Pages 7 0920-9964/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.schres.2013.07.046 Contents lists available at ScienceDirect Schizophrenia Research journal homepage: www.elsevier.com/locate/schres Please cite this article as: Ferraro, L., et al., Cannabis users have higher premorbid IQ than other patients with first onset psychosis, Schizophr. Res. (2013), http://dx.doi.org/10.1016/j.schres.2013.07.046