PATIENTS WITH THEIR FIRST EPISODE OF PSYCHOSIS (FEP) WHO USE CANNABIS HAVE NORMAL PREMORBID IQ

Cannabis use is highly prevalent among people with schizophrenia and, coupled with impaired cognition, is thought to heighten the risk of illness onset. Paradoxically, several studies report lifetime cannabis use as a predictor of a better cognitive performance in psychotic patients. This case/control study was conducted in order to observe in a First Episode group the association between cannabis use lifetime and two measures of general cognition: current and pre-morbid IQ. The data are derived from the GAP study, a case-control study of first-episode psychosis (FEP) - South London and Maudsley Mental Health NHS Foundation Trust. 279 consenting subjects: 119 FEP patients (age 29.6±8.5; 70% males) and 160 healthy controls (age 29.6±10.8; 52% males), completed neuropsychological tests able to measure current IQ (WAIS-III, short version) and pre-morbid IQ (WTAR). They all completed a Cannabis Experience Questionnaire about cannabis and other drugs use. In each group, those that had used cannabis lifetime what dopes lifetime meanwere compared to those who never had used cannabis, for IQ and pre-morbid IQ scores. A 2x3 factorial ANCOVA (Groups [cases, controls] × drugs [no drugs, only cannabis, cannabis andother drugs]) was carried out in order to check the significance of these two fixed factors on IQ and WTAR. Finally, we compared IQ and pre-morbid IQ between “affective” and “non affective” psychosis by cannabis use. Patients performed significantly worse than controls in IQ (p<0.0001) and premorbid IQ (p<0.0001). ANCOVAs showed significant higher IQ (p=0.001) and pre-morbid IQ (p=0.011) in people who smoked cannabis lifetime in the case group and no differences in control sample, either in IQ (p=0.757) and in WTAR scores (p=0.156). Factorial ANCOVAs confirmed that FEP group was significantly affected by drug on IQ (p=0.006). Interestingly, there was not significant differences in WTAR between cases and controls if they had used only cannabis lifetime (p=0.284). This suggests that patients who used only cannabis lifetime were more similar in pre-morbid IQ to controls. Drug use, considered alone, was more important than diagnosis in determining cognitive differences between subjects, especially in non affective psychosis. Our results confirm a strong relationship between cannabis use lifetime and higher cognitive performance in patients. First episode subject who used only cannabis lifetime seem to be a high pre-morbid functioning sub-group, which does not show significant differences with control group. Non affective psychosis is the most impaired diagnostic group, although people in this group with cannabis use lifetime show a significantly higher pre-morbid IQ than others, more similar to affective psychosis group. These findings confirm a different relationship of cannabis with cognitive function in FEP patients and controls, and in different diagnostic groups. They also suggest that the relationship between higher cognitive functioning and cannabis use could be read in the direction of pre-existing less impaired cognitive functioning in which cannabis could be a marker of a better pre-morbid social functioning.