Effects of cocaine and alcohol, alone and in combination, on human learning and performance

The acute effects of cocaine hydrochloride (4 to 96 mg/70 kg) and alcohol (0 to 1.0 g/kg), administered alone and in combination, were assessed in two experiments with human volunteers responding under a multiple schedule of repeated acquisition and performance of response chains. Subjects were intermittent users of cocaine and regular drinkers who were not cocaine or alcohol dependent. Alcohol was mixed with orange juice and ingested in six drinks within 30 min; cocaine was administered intranasally 45 min after completion of drinking. In each component of the multiple schedule, subjects completed response sequences using three keys of a numeric keypad. In the acquisition component, a new sequence was learned each session. In the performance component, the response sequence always remained the same. Results were consistent in both experiments, despite variations in the order in which the drugs were tested alone and in combination. Alcohol administered alone increased overall percentage of errors and decreased rates of responding in the acquisition component, whereas responding in the performance component generally was unaffected. Cocaine administered alone decreased rates of responding but did not affect accuracy of responding in the acquisition component, and enhanced accuracy of responding without affecting rates of responding in the performance component. The combined doses of cocaine and alcohol attenuated the effects observed with alcohol and cocaine alone. These results suggest that, under the conditions investigated in this study, (a) alcohol produces greater behavioral disruption than cocaine or cocaine-alcohol combinations, (b) cocaine and alcohol each attenuate effects of the other, and (c) such attenuation is most pronounced for cocaine attenuating the disruptive effects of alcohol.