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Solowij N, Stephens RS, Roffman RA, et al. Cognitive Functioning of Long-term Heavy Cannabis Users Seeking Treatment. JAMA. 2002;287(9):1123–1131. doi:10.1001/jama.287.9.1123
Author Affiliations: National Drug and Alcohol Research Centre, University of New South Wales, Sydney, and Department of Psychology, University of Wollongong, Wollongong (Dr Solowij), New South Wales, Australia; Department of Psychology, Virginia Polytechnic Institute and State University, Blacksburg, Va (Dr Stephens); Innovative Programs Research Group, School of Social Work, University of Washington, Seattle (Dr Roffman); Department of Community Medicine (Dr Babor and Mss McRee and Vendetti) and Department of Psychiatry (Dr Kadden), University of Connecticut Health Center, Farmington; and The Village South Inc, Miami, Fla (Drs Miller and Christiansen).
Context Cognitive impairments are associated with long-term cannabis use, but
the parameters of use that contribute to impairments and the nature and endurance
of cognitive dysfunction remain uncertain.
Objective To examine the effects of duration of cannabis use on specific areas
of cognitive functioning among users seeking treatment for cannabis dependence.
Design, Setting, and Participants Multisite retrospective cross-sectional neuropsychological study conducted
in the United States (Seattle, Wash; Farmington, Conn; and Miami, Fla) between
1997 and 2000 among 102 near-daily cannabis users (51 long-term users: mean,
23.9 years of use; 51 shorter-term users: mean, 10.2 years of use) compared
with 33 nonuser controls.
Main Outcome Measures Measures from 9 standard neuropsychological tests that assessed attention,
memory, and executive functioning, and were administered prior to entry to
a treatment program and following a median 17-hour abstinence.
Results Long-term cannabis users performed significantly less well than shorter-term
users and controls on tests of memory and attention. On the Rey Auditory Verbal
Learning Test, long-term users recalled significantly fewer words than either
shorter-term users (P = .001) or controls (P = .005); there was no difference between shorter-term
users and controls. Long-term users showed impaired learning (P = .007), retention (P = .003), and retrieval
(P = .002) compared with controls. Both user groups
performed poorly on a time estimation task (P<.001
vs controls). Performance measures often correlated significantly with the
duration of cannabis use, being worse with increasing years of use, but were
unrelated to withdrawal symptoms and persisted after controlling for recent
cannabis use and other drug use.
Conclusions These results confirm that long-term heavy cannabis users show impairments
in memory and attention that endure beyond the period of intoxication and
worsen with increasing years of regular cannabis use.
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