Abstract
Rationale
Cognitive deficits are commonly found both in patients with schizophrenia (SCH) and in people with cannabis use disorders (CUD). Surprisingly, some small recent studies reported better cognitive performance in SCH patients with comorbid cannabis use disorders (SCH + CUD) compared to other SCH patients.
Objectives
The aim of the present study was to investigate the residual impact of CUD and specific patterns of consumption on cognition in a larger sample of SCH + CUD patients.
Methods
We administered a cognitive test battery to 34 SCH and 35 currently abstinent SCH + CUD patients. We explored the association between patterns of cannabis consumption and cognitive performance. Potential confounds with influence on cognitive ability were assessed and controlled for.
Results
SCH + CUD patients had poorer academic achievements and lower vocabulary scores, but they performed better in tests of verbal and working memory, visuomotor speed and executive function (p < .05). More frequent cannabis use was associated with better performance in attention and working memory tasks.
Conclusions
Although our findings might be interpreted as beneficial effect of cannabis use on cognition in patients with schizophrenia, we favorise an alternative interpretation: in our view, the better cognitive functioning of SCH + CUD patients may rather reflect a relatively lower vulnerability to psychosis compared to the SCH group. Lower vulnerability may correspond to a higher level of functioning such as cognitive ability. This conclusion is consistent with the view of cannabis playing a critical role in the manifestation of psychosis in at least some of the SCH + CUD patients.
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Acknowledgements
The authors want to thank Laura Kranaster, Sonja Gross, Karsten Heekeren, Knut Schnell and Anna Neukirch for their assistance in recruiting the subjects. In addition, the authors want to thank Ralf Pukrop for his help in selecting the neuropsychological tests. Finally, we want to thank Karsten Blume for his assistance in testing the subjects.
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The authors declare that they have no conflicts of interest.
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Funding sources did not play any role in conducting or reporting this research.
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Schnell, T., Koethe, D., Daumann, J. et al. The role of cannabis in cognitive functioning of patients with schizophrenia. Psychopharmacology 205, 45–52 (2009). https://doi.org/10.1007/s00213-009-1512-9
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DOI: https://doi.org/10.1007/s00213-009-1512-9