Cannabis use and premorbid functioning as predictors of poorer neurocognition in schizophrenia spectrum disorder.

Background: Evidence of associations between neurocognitive function and cannabis use in schizophrenia is inconclusive. However, direct measures of cannabis intake and premorbid function are rarely explored in this context. We investigated the relation between cannabis use, determined by its presence in urine, and neurocognitive functioning in schizophrenia controlling for the potential bias of premorbid functioning.
Methods: Naturalistic study of 364 patients with schizophrenia spectrum disorder from catchment areas in Oslo, Norway. Hierarchical multiple regression analyses were used to assess the relationship between cannabis in urine and measures of neurocognitive functioning, with adjustment for confounders, including premorbid functioning.
Results: Cannabis was detected in the urine of 21 patients, who had significant dysfunction in several neurocognitive domains independent of a current diagnosis of cannabis abuse. However, level of premorbid functioning explained the associations for all measures.
Conclusion: Differences in premorbid functioning may explain apparent differences in neurocognitive function between schizophrenia spectrum patients using cannabis or not. The findings suggest that illness-related traits present early in life can affect both later cannabis use and neurocognition, probably by complex mechanisms.
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