The Impact of Cannabis Use on Cognitive Functioning in Patients With Schizophrenia: A Meta-analysis of Existing Findings and New Data in a First-Episode Sample.
Yücel M, Bora E, Lubman DI, Solowij N, Brewer WJ, Cotton SM, Conus P, Takagi MJ, Fornito A, Wood SJ, McGorry PD, Pantelis C.Melbourne Neuropsychiatry Centre, Department of Psychiatry, University of Melbourne and Melbourne Health, National Neuroscience Facility, Alan Gilbert Building, 161 Barry Street, Carlton South, Victoria 3053, Australia.
Abstract
Cannabis use is highly prevalent among people with schizophrenia, and coupled with impaired cognition, is thought to heighten the risk of illness onset. However, while heavy cannabis use has been associated with cognitive deficits in long-term users, studies among patients with schizophrenia have been contradictory.This article consists of 2 studies. In Study I, a meta-analysis of 10 studies comprising 572 patients with established schizophrenia (with and without comorbid cannabis use) was conducted. Patients with a history of cannabis use were found to have superior neuropsychological functioning. This finding was largely driven by studies that included patients with a lifetime history of cannabis use rather than current or recent use.
In Study II, we examined the neuropsychological performance of 85 patients with first-episode psychosis (FEP) and 43 healthy nonusing controls. Relative to controls, FEP patients with a history of cannabis use (FEP + CANN; n = 59) displayed only selective neuropsychological impairments while those without a history (FEP – CANN; n = 26) displayed generalized deficits. When directly compared, FEP + CANN patients performed better on tests of visual memory, working memory, and executive functioning. Patients with early onset cannabis use had less neuropsychological impairment than patients with later onset use.
Together, these findings suggest that patients with schizophrenia or FEP with a history of cannabis use have superior neuropsychological functioning compared with nonusing patients. This association between better cognitive performance and cannabis use in schizophrenia may be driven by a subgroup of “neurocognitively less impaired” patients, who only developed psychosis after a relatively early initiation into cannabis use.
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[...] of cannabis increasing greatly during that decade. (Read up on all my coverage of studies showing cannabis-using schizophrenics have better cognitive functioning, how THC may help schizophrenics, how schizophrenia has not increased with cannabis use increasing, [...]
Maia Szalavitz recently covered some of this work in her excellent story for Time.com here:
http://www.time.com/time/health/article/0,8599,2005559,00.html
Two issues may be at play here. 1) Cannabinoids may be neuroprotective in certain patients with schizophrenia; or 2) schizophrenics who use marijuana are more likely to be highly functional than those who don’t use it. My guess is the answer likely lies more in the latter explanation than in the former, but there is yet non consensus. But this result (higher cognitive functioning in mj using patients w/ SZ) has been replicated numerous times now.
This is interesting news that I didn’t see anywhere on the tube this morning. Go figure!