Effects of chronic marijuana use on human cognition.
Impairments of human cognition and learning following chronic marijuana use are of serious concern, but have not been clearly demonstrated. To determine whether such impairments occurred, this study compared performance of adult marijuana users and non-users (N = 144 and N = 72, respectively) matched on intellectual functioning before the onset of drug use, i.e., on scores from standardized tests administered during the fourth grade of grammar school (Iowa Tests of Basic Skills). Subjects were given the twelfth grade versions of these tests (Iowa Tests of Educational Development) and other, computerized cognitive tests in successive test sessions. "Heavy" marijuana use (defined by use seven or more times weekly) was associated with deficits in mathematical skills and verbal expression in the Iowa Tests of Educational Development and selective impairments in memory retrieval processes in Buschke's Test. The retrieval impairments were restricted to words that were easy to visualize. Impairments depended on the frequency of chronic marijuana use, i.e., "light" and "intermediate" marijuana use (defined by use one to four and five to six times weekly, respectively) were not associated with deficits. Intermediate use was associated with superior performance in one condition ("fuzzy" concepts) of a Concept Formation test.
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Department of Anesthesia, University of Iowa, Iowa City 52242.
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D000293:Adolescent; D000328:Adult; D000437:Alcoholism / Q000523:psychology; D001245:Association Learning / Q000187:drug effects; D002908:Chronic Disease; D003071:Cognition / Q000187:drug effects*; D003210:Concept Formation / Q000187:drug effects; D005260:Female; D005608:Free Association; D006801:Humans; D007858:Learning / Q000187:drug effects; D008297:Male; D008385:Marijuana Smoking / Q000523:psychology*; D008568:Memory / Q000187:drug effects; D008606:Mental Processes / Q000187:drug effects; D011597:Psychomotor Performance / Q000187:drug effects; D019966:Substance-Related Disorders / Q000523:psychology; D014825:Vocabulary