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09-09-2010 | Mental health | Article

Cognitive effects of cannabis use ‘minimal’ in schizophrenia patients


Free abstract

MedWire News: Cannabis use has little effect on cognitive performance in schizophrenia patients or healthy individuals, Australian research suggests.

"It has been suggested that cannabis use in healthy individuals can produce cognitive impairment which resembles that which is evident in schizophrenia," explain K Scholes and M Martin-Iverson from the University of Western Australia in Perth.

They add that "it may be hypothesized that patients with schizophrenia who use cannabis would show even further decrements in performance of these cognitive processes."

To investigate, the researchers enrolled 71 schizophrenia patients, of whom 22 were cannabis users, and 71 mentally healthy individuals (controls), of whom 36 were cannabis users.

All of the participants were assessed for attentional control, working memory, and executive functioning using the Stroop task, the letter-number sequencing and spatial span subtests of the Wechsler Memory Scale, and the Wisconsin Card Sorting Test (WCST), respectively.

Between-group analysis showed that patients with schizophrenia (both cannabis users and non-users) performed significantly worse on all of the neuropsychological tests compared with controls.

However, within-group analysis revealed no significant differences between cannabis users and non-users in the schizophrenia or control groups in neuropsychological test performance, apart from the perseveration subsections of the WCST.

Specifically, among schizophrenia patients, cannabis users had more non-perseverative errors on the WCST than non-users, and among controls, cannabis users had increased perseveration compared with non-users.

Scholes and Martin-Iverson conclude in the journal Psychological Medicine: "It appears that cannabis use in both healthy individuals and patients with schizophrenia has only very subtle effects on performance of the neuropsychological tasks administered here, which have long been established to index characteristic disturbances in schizophrenia."

They add: "As such, it may be that chronic cannabis use has no additive effect on cognitive dysfunction in schizophrenia."

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Mark Cowen

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