Author Topic: Early Use of Cannabis May Improve Cognitive Functioning in Subgroup of Patients  (Read 4643 times)

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Fwd: Early Use of Cannabis May Improve Cognitive Functioning in Subgroup
of Patients With Schizophrenia
Tue, 31 Aug 2010 15:44:15 +0000 (UTC)
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     From Medscape Medical News
     Early Use of Cannabis May Improve Cognitive Functioning in Subgroup
of Patients With Schizophrenia

     Caroline Helwick

     August 29, 2010 (Amsterdam, The Netherlands) — Although the use of
cannabis is believed to heighten the risk for schizophrenia and
psychotic episodes, a meta-analysis of existing data has yielded new
findings from Australian researchers that suggest the associations are
complex and, surprisingly, early use may improve cognitive function
among those patients who are relatively less neurocognitively impaired.

     At the 23rd European College of Neuropsychopharmacology Congress,
Murat Yücel, PhD, and colleagues from the University of Melbourne in
Australia reported that patients with schizophrenia having a history of
cannabis use had superior neuropsychological functioning compared with
nonusers. The conclusion was drawn from their meta-analysis of 10
studies involving 572 patients with schizophrenia.

     Furthermore, from their own study of 85 individuals with
first-episode psychosis (FEP), they found that regular users of cannabis
performed better on tests of visual memory, working memory, and
executive functioning. In addition, patients who began using cannabis by
the age of 16 years (ie, early users) had less neuropsychological
impairment than patients who began using cannabis later.

     "Patients with schizophrenia generally use more cannabis than the
general population, and there must be a reason. As researchers, we are
interested in what that association is about," Dr. Yücel told Medscape
Medical News. "Our key finding is that the relationship between cannabis
and psychosis is complex. In healthy persons, heavy or long-term use of
cannabis has negative effects on cognition and memory, but in psychosis
the relationship is apparently not as clear."

     The findings of both the meta-analysis and experimental data
together indicate that the use of cannabis in established schizophrenia
and also in FEP is associated with better cognitive performance than the
lack of using cannabis, although this does not indicate that it is
neuroprotective, he said.

     Global Cognition Index Better With Cannabis Use

     In the meta-analysis, neuropsychological variables were grouped
according to the 6 cognitive domains of the Measurement and Treatment
Research to Improve Cognition in Schizophrenia battery. A global
cognition index was calculated by averaging effect sizes from each
domain for each study.

     Patients with a history of cannabis use were found to have superior
neuropsychological functioning. The finding was largely driven by
studies that included patients with a lifetime history of cannabis use
rather than current or recent use. In 1 study, greater frequency of
cannabis use was associated with better cognitive performance. Overall,
earlier starting age of cannabis use (16 years or younger) was
associated with superior cognitive performance compared with later use,
Dr. Yucel reported.

     "We found that patients with a history of cannabis use had superior
neuropsychological functioning, with an average effect size of 0.50
across all the cognitive domains investigated," he said.

     The mean weighted effect size associated with lifetime cannabis use
was 0.55 (P = .001) for global cognition, 0.65 (P = .001) for processing
speed, and 0.64 (P = .003) for working memory.

     New Data in FEP

     In the second study, 85 FEP patients were compared with 43 healthy
non–cannabis-using controls with FEP. Regular use was defined as at
least 2 years of use and use of at least 2 g per week. None of the FEP
cannabis users had ever used cannabis regularly (ie, weekly for at least
12 months). Healthy controls had no current or past history of illicit
substance abuse or dependence.

     Relative to controls, FEP cannabis users displayed only selective
neuropsychological impairments, whereas FEP nonusers displayed
generalized deficits. When the 2 clinical groups were directly compared,
the cannabis users 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 of use. The early cannabis users were younger than the later-onset
users but did not differ in duration or monthly quantity of cannabis
use, diagnosis, treatment, or antipsychotic levels, he added.

     The investigators speculated that age of onset of cannabis use as a
moderator of the association between cannabis and psychotic illness may
be related to the effects of cannabis on the developing brain. "We
contend that the association between better cognitive performance and
cannabis use is driven by a subgroup of ‘neurocognitively less impaired'
patients who only develop psychosis after early initiation into cannabis
use. As such, early cannabis use may be an independent risk factor for
the development of psychosis," he said.

     "In other words, cannabis is potentially tipping some persons over
the edge, maybe in combination with a genetic predisposition. We wonder
if, in the absence of cannabis, they may not have developed the
illness," he added.

     The investigators are following up the patients and will soon have
10-year data on approximately 80% of the cohort.

     "It will be important to see the long-term data," commented Richard
Tranter, MBChB, consultant psychiatrist at the North West Wales NHS
Trust, Bangor, United Kingdom, who said he was intrigued by these
findings. "A large body of data is suggesting that cannabis can be an
important predisposing factor for schizophrenia. The current study
suggests, however, there may be a group that is different—who, if they
are exposed to cannabis, may sustain damage perhaps because of some
elementary factors in the brain, but if you get them off cannabis they
may be fine. The other possibility is that cannabis is actually having a
positive effect. We will have to wait for the 10-year data to determine

     The study author and Dr. Tranter have disclosed no relevant
financial relationships.

     23rd European College of Neuropsychopharmacology (ECNP) Congress:
Abstract P.3.a.005. Presented August 29, 2010.

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