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Attempts to determine whether particular recreational drugs cause lasting cognitive impairment are confounded by lack of predrug neuropsychological testing, polysubstance use, malnutrition, and other social deprivation. Heavy ethanol use causes dementia as a consequence of both nutritional deficiency and direct neurotoxicity, but lesser degrees of ethanol might be protective against dementia. If cocaine causes permanent cognitive impairment, the mechanism might be vascular. Recent studies suggest that heavy marijuana use has persistent detrimental effects on cognition. Studies with other agents have been inconsistent.