Conditioned tolerance to the tachycardia effect of ethanol in humans.

Human subjects were given a series of oral ethanol administrations in one environment and an equal number of placebo administrations in another distinct environment. Tolerance (a decreasing response with repeated administrations) to the tachycardia effect of ethanol was observed; no consistent changes in heart rate followed placebo administrations. Subsequently, tolerance to a test dose of ethanol administered in the environment normally associated with placebo was reduced relative to that in response to a dose administered in the usual ethanol environment. This demonstration of environment-specificity in a human drug tolerance experiment replicates previous reports from animal studies, and is interpreted according to a Pavlovian conditioning model of drug tolerance.