Background: Several studies report that patients with psychosis who
used cannabis have a better cognitive performance than those whodid not (Rabin et al. 2011). In a previous study we found out a higher
premorbid IQ, and a better IQ in psychotic patients who smoked
cannabis in their lifetime, and our findings were consistent with the
idea that this association is due to a better premorbid functioning
rather than to an ameliorative effect of cannabis use on cognitive
performance (Ferraro et al., 2013). A number of authors have
hypothesized that psychotic patients who consume cannabis constitute
a differentiated subgroup of patients that have better cognitive
and social skills, necessary to engage in illegal drug consumption,
than non-using patients (Compton et al., 2011; L\uf8berg et al., 2014;
Arnold et al., 2015). Given that the prevalence, and patterns, of
cannabis use are culturally driven, we wanted 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 (England, Italy, Spain, France, the Netherlands)
as part of the EUGEI-STUDY.
Methods: 1.745 people (746 cases; 999 controls) completed the
assessment for Intellectual Quotient (IQ) (WAIS-brief version) premorbid
adjustment (Premorbid Adjustment Scale \u2013 PAS) and cannabis
use (CEQ-Revised). We first performed a factor analysis on PAS
components, by obtaining two main factors: \u201cPremorbid Social
Adjustment\u201d (PSA) and \u201cPremorbid Academic Adjustment\u201d (PAA). We
therefore performed linear mixed models with IQ, PSA, and PAA as
dependent variables and cannabis lifetime (Yes/No), subject status
(Cases/Controls), gender and age as independent variables.
Results: Across all countries, IQ was higher in those patients who
smoked cannabis in their lifetime compared to those who did not
(P = 0.027). This IQ difference was only 3 points and was the same for
cases and healthy controls (P = 0.949). Similarly, patients who had
smoked cannabis in their lifetime showed better PSA scores than non
users (P = 0.009). The difference in PSA score between cannabis-users
and non-users was significantly greater in cases than controls
(P = 0.038). Conversely, across all countries, PAA resulted worst in
patients who smoked cannabis lifetime than patients who did not
(Po0.001) and this PAA score difference was the same for cases and
controls (P = 0.693).
Discussion: Our cannabis-using FEP patients have higher IQ, better PSA
and lower PAA than non user patients across 5 different European
countries. Starting from these preliminary results, we can conclude
that a better PSA is significantly associated with cannabis use in FEP
patients. Nevertheless, in an exploratory analysis, a better IQ resulted
related to a better PAA (o0.001) but not to PSA (P = 0.260); thus
indicating an independent relationship of IQ and PSA with cannabis
use. Further analysis are required in order to model these multivariate
relationships