Effects of cannabis use status on cognitive function, in males with schizophrenia.

Cognitive impairment and cannabis use are common among patients with schizophrenia. However, the moderating role of cannabis on cognition remains unclear. We sought to examine cognitive performance as a function of cannabis use patterns in schizophrenia. A secondary aim was to determine the effects of cumulative cannabis exposure on cognition. Cognition was assessed in male outpatients with current cannabis dependence (n=18) and no current cannabis use disorders (n=29). We then parsed non-current users into patients with lifetime cannabis dependence (n=21) and no lifetime cannabis dependence (n=8). Finally, as an exploratory analysis, we examined relationships between cumulative cannabis exposure and cognition in lifetime dependent patients. Cross-sectional comparisons suggest that lifetime cannabis users demonstrate better processing speed than patients with no lifetime dependence. Exploratory analyses indicated that patients with current dependence exhibited robust negative relationships between cumulative cannabis exposure and cognition; these associations were absent in former users. Cannabis status has minimal effects on cognition in males with schizophrenia. However, cumulative cannabis exposure significantly impairs cognition in current, but not former users, suggesting that the state dependent negative effects of cannabis may be reversed with sustained abstinence. Prospective studies are needed to confirm these findings.