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Non-acute (residual) neurocognitive effects of cannabis use: A meta-analytic study

Published online by Cambridge University Press:  01 July 2003

IGOR GRANT
Affiliation:
Department of Psychiatry, University of California, San Diego Center for Medicinal Cannabis Research, University of California, San Diego Veterans Affairs Healthcare System, San Diego, CA HIV Neurobehavioral Research Center, University of California, San Diego
RAUL GONZALEZ
Affiliation:
SDSU/UCSD Joint Doctoral Program in Clinical Psychology HIV Neurobehavioral Research Center, University of California, San Diego
CATHERINE L. CAREY
Affiliation:
SDSU/UCSD Joint Doctoral Program in Clinical Psychology HIV Neurobehavioral Research Center, University of California, San Diego
LOKI NATARAJAN
Affiliation:
HIV Neurobehavioral Research Center, University of California, San Diego Department of Family and Preventive Medicine, University of California, San Diego
TANYA WOLFSON
Affiliation:
HIV Neurobehavioral Research Center, University of California, San Diego

Abstract

The possible medicinal use of cannabinoids for chronic diseases emphasizes the need to understand the long-term effects of these compounds on the central nervous system. We provide a quantitative synthesis of empirical research pertaining to the non-acute (residual) effects of cannabis on the neurocognitive performance of adult human subjects. Out of 1,014 studies retrieved using a thorough search strategy, only 11 studies met essential a priori inclusion criteria, providing data for a total of 623 cannabis users and 409 non- or minimal users. Neuropsychological results were grouped into 8 ability domains, and effect sizes were calculated by domain for each study individually, and combined for the full set of studies. Using slightly liberalized criteria, an additional four studies were included in a second analysis, bringing the total number of subjects to 1,188 (i.e., 704 cannabis users and 484 non-users). With the exception of both the learning and forgetting domains, effect size confidence intervals for the remaining 6 domains included zero, suggesting a lack of effect. Few studies on the non-acute neurocognitive effects of cannabis meet current research standards; nevertheless, our results indicate that there might be decrements in the ability to learn and remember new information in chronic users, whereas other cognitive abilities are unaffected. However, from a neurocognitive standpoint, the small magnitude of these effect sizes suggests that if cannabis compounds are found to have therapeutic value, they may have an acceptable margin of safety under the more limited conditions of exposure that would likely obtain in a medical setting. (JINS, 2003, 9, 679–689.)

Type
Research Article
Copyright
© 2003 The International Neuropsychological Society

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