Better IQ but worse Premorbid Academic Adjustment in cannabis-users psychotic patients: another brick in the intuition

Purpose: several studies report that patients with psychosis who used cannabis in their lifetime have a better cognitive performance than those who did not and this association is most likely due to a better premorbid functioning. We aimed to test the hypothesis of a better premorbid functioning in First Episode Psychosis (FEP) cannabis-using and non-using patients coming from different European countries. Materials and Methods: 1.745 people (746 cases; 999 healthy controls) completed the assessment for Intellectual Quotient (IQ) (WAIS-brief version) premorbid adjustment (Premorbid Adjustment Scale – PAS) and cannabis use (CEQ-Revised). We first obtained two main factors from PAS: “Premorbid Social Adjustment” (PSA) and “Premorbid Academic Adjustment” (PAA). We therefore performed linear mixed models with IQ, PSA, and PAA as dependent variables and cannabis lifetime (Yes/No) and subject status (Cases/Controls) as independent variables. Results: across all countries, IQ was higher in cannabis users patients compared to non users (p=0.027). Conversely, PAA resulted worst in cannabis-users patients than non users (p<0.001). Neverthless, cannabis-users patients showed better PSA scores than non users (p=0.009) and this difference was significantly greater in patients than controls (p=0.038). Moreover, a better IQ resulted related to a better PAA (<0.001) but not to PSA (p=0.260). Conclusions: a better IQ is not directly predictable by a better adjustment at school between 12 and 16 years (PAA), even if these two scores are positivelty correlated. Additionally we can speculate an independent relationship of IQ and a better sociability between 12 and 16 years (PSA) with cannabis use.