Interaction between Marihuana and Ethanol: Effects on Psychomotor Performance

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Abstract
This is a report of the results of a placebo-controlled study in which the effects of the interaction between ethanol and marijuana on drug plasma concentrations, subjective ratings of intoxication, heart rate acceleration, and psychomotor performance were investigated. Six healthy, male, paid volunteers, moderate users of ethanol and marijuana, participated in the study. Ethanol (0.42 g/kg, 0.85 g/kg, or placebo) was administered over a 30-min interval. Fifteen minutes later the subjects smoked, in their customary manner, NIDA cigarettes containing 2.4% or 0.0004% (placebo) .delta.-9-tetrahydrocannabinol (THC). Each subject was tested in a single-blind, latin-square crossover design with the following six conditions: placebo ethanol/placebo marijuana; low dose ethanol/placebo marijuana; high dose ethanol/placebo marijuana; placebo ethanol/marijuana; low dose ethanol/marijuana; and high dose ethanol/marijuana. The variables measured in the study were: (a) subjective rating of ethanol and/or marijuana intoxication; (b) heart rate; (c) accuracy and latency of response in the Simulator Evaluation of Drug Impairment (SEDI) task; (d) blood ethanol concentration by gas chromatography; and (e) plasma concentration of THC by radioimmunoassay. The results indicate that the decrements due to ethanol in performance of skills necessary to drive an automobile were significantly enhanced by marijuana in an additive and perhaps synergistic manner. The administration of ethanol prior to marijuana smoking did not produce significant effects on the subjective rating of "high", heart rate acceleration, or THC plasma concentration.