Joint effects of d-amphetamine and ethanol or pentobarbital in pigeons.

Drug interactions were examined in pigeons keypecking under a multiple fixed ratio 30-response, fixed interval 5-minute (mult FR 30, FI 5-min) schedule of food presentation. Low to intermediate doses of d-amphetamine attenuated the rate-decreasing effects of ethanol under both components of the multiple schedule; however, these same doses of d-amphetamine seldom attenuated the rate-decreasing effects of pentobarbital. Increases in rates of responding produced by ethanol or pentobarbital under FI components were often enhanced following low to intermediate doses of d-amphetamine. Higher doses of d-amphetamine generally enhanced the rate-decreasing effects produced by either ethanol or pentobarbital alone. Results indicate that the joint effects of two drugs cannot be predicted from a knowledge of either their individual or their rate-dependent effects.