Cannabis use is highly prevalent among people with schizophrenia and,coupled with impaired cognition, is thought to heighten the risk of illnessonset. Paradoxically, several studies report lifetime cannabis use asa predictor of a better cognitive performance in psychotic patients. Thiscase/control study was conducted in order to observe in a First Episodegroup the association between cannabis use lifetime and two measures ofgeneral cognition: current and pre-morbid IQ. The data are derived fromthe GAP study, a case-control study of first-episode psychosis (FEP) - SouthLondon and Maudsley Mental Health NHS Foundation Trust. 279 consentingsubjects: 119 FEP patients (age 29.6±8.5; 70% males) and 160 healthycontrols (age 29.6±10.8; 52% males), completed neuropsychological testsable to measure current IQ (WAIS-III, short version) and pre-morbid IQ(WTAR). They all completed a Cannabis Experience Questionnaire aboutcannabis and other drugs use. In each group, those that had used cannabislifetime what dopes lifetime meanwere compared to those who never hadused 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 twofixed factors on IQ and WTAR. Finally, we compared IQ and pre-morbid IQbetween “affective” and “non affective” psychosis by cannabis use. Patientsperformed significantly worse than controls in IQ (p<0.0001) and premorbidIQ (p<0.0001). ANCOVAs showed significant higher IQ (p=0.001)and pre-morbid IQ (p=0.011) in people who smoked cannabis lifetime inthe 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 groupwas significantly affected by drug on IQ (p=0.006). Interestingly, there wasnot significant differences in WTAR between cases and controls if they hadused only cannabis lifetime (p=0.284). This suggests that patients who usedonly cannabis lifetime were more similar in pre-morbid IQ to controls.Drug use, considered alone, was more important than diagnosis in determiningcognitive differences between subjects, especially in non affectivepsychosis. Our results confirm a strong relationship between cannabis uselifetime and higher cognitive performance in patients. First episode subjectwho used only cannabis lifetime seem to be a high pre-morbid functioningsub-group, which does not show significant differences with control group.Non affective psychosis is the most impaired diagnostic group, althoughpeople in this group with cannabis use lifetime show a significantly higherpre-morbid IQ than others, more similar to affective psychosis group. Thesefindings confirm a different relationship of cannabis with cognitive functionin FEP patients and controls, and in different diagnostic groups. They alsosuggest that the relationship between higher cognitive functioning andcannabis use could be read in the direction of pre-existing less impairedcognitive functioning in which cannabis could be a marker of a betterpre-morbid social functioning.
|Number of pages||2|
|Publication status||Published - 2012|