The Neuropsychological consequences of cannabis use in schizophrenia: a preliminary analysis

Background: There has been considerable controversy regarding the possible causal role of cannabis use in the development of schizophrenia; there have also been contradictory findings concerning the impact of cannabis use on neuropsychological function in schizophrenia and in non-psychiatric samples. This paper presents preliminary data comparing neuropsychological task performances of people with a diagnosis of schizophrenia with and without cannabis use. Methods: Participants included 17 individuals with a diagnosis of schizophrenia (10 without cannabis use, plus 3 with current cannabis use, combined with 4 for whom cannabis use was significant at onset but is no longer in use, to make the 7 members of the cannabisusing group). All participants were tested on neuropsychological measures covering a range of cognitive domains (executive functioning, memory, learning, attention and information processing speed). Psychopathological assessments (eg depression, symptom ratings) and detailed drug use measures were also conducted. Results: The cannabis-using group was more symptomatic, had lower levels of current intelligence and showed greater impulsivity as indexed by the CPT, compared with the non-cannabis-using group. There were trends toward greater recognition memory deficits and arousal deficits as indexed by the CPT in the cannabis-using group. Conclusions: Cannabis use in schizophrenia may be associated with greater symptom severity and increased deficits in impulse control and current intelligence. Although preliminary, these results are inconsistent with the self-medication hypothesis, as symptoms are exacerbated by cannabis.