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May 22, 1996

Cognitive Effects of Marijuana

JAMA. 1996;275(20):1547. doi:10.1001/jama.1996.03530440025029

To the Editor.  —The report by Drs Pope and Yurgelun-Todd1 on residual cognitive effects of heavy marijuana use highlights the importance of recognizing that chronic and abusive use of psychotropic compounds such as marijuana may have serious negative sequelae. However, the strength of these conclusions are not without methodological caution. Perhaps the most important of these concerns drawing inferences from research based on short-term clinical trials.Deficits in intellectual and neuropsychological functioning may represent antecedents, concomitants, or consequences of chronic drug (ie, marijuana) use. The short-term nature of their study prohibits teasing apart these temporal and often confounding relationships. Comparison with matched controls represents a potentially effective means of statistically controlling for underlying differences (ie, premorbid psychopathology). However, there are a number of psychosocial conditions that cannot be statistically corrected through the use of matched controls. Studies of adolescents have consistently found that low self-esteem, poor social (eg, assertive)