The neuropsychological correlates of cannabis use in schizophrenia: Lifetime abuse/dependence, frequency of use, and recency of use

This study examined the relationship between neuropsychological performance and three different indices of cannabis use in schizophrenia. These indices were DSM-IV lifetime abuse/dependence, frequency of use, and recency of use. Sixty males with schizophrenia/schizoaffective disorder and 17 healthy males were recruited. The two groups were matched for age, years of education, and premorbid IQ. Medical history, substance use, and psychiatric symptoms were assessed. A neuropsychological battery was also administered to assess attention/processing speed, executive functions, memory, and perceptual organisation. Substance use within 24 hours of cognitive assessment was screened by urine analysis, and a range of confounds were controlled. In the schizophrenia group, 44 participants met DSM-IV criteria for lifefime cannabis abuse/dependence. in addition, there were three mutually exclusive frequency-of-cannabis-use subgroups comprising "high" frequency users (n=11), "medium" frequency users (n=7), and "low" frequency users (n=34) over the preceding year. There were also four mutually exclusive recency-of-cannabis-use categories comprising "cannabis abuse/dependence in the past week" (n=11 users), "non-dependent cannabis use in the past week" (n=7 users), "non-dependent cannabis use in the past month, but prior to the past week" (n=7 users), and "non-dependent cannabis use prior to the past month" (n=9 users). The control group performed better than the schizophrenia group in all cognitive domains. Within the schizophrenia group, a larger proportion of participants with lifetime cannabis abuse/dependence demonstrated better performance than those without lifetime abuse/dependence on a component of psychomotor speed. Frequency and recency of cannabis use were also associated with better neuropsychological performance, predominantly in the domains of attention/processing speed and executive functions. In conclusion, cannabis use is associated with enhanced cognitive functioning in schizophrenia. Implications of the results, I imitations of the study, and directions for future research are discussed. Crown Copyright (C) 2007 Published by Elsevier B.V. All rights reserved.