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 lifetime 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, limitations of the study, and directions for future research are discussed.