Effects of d-amphetamine and ethanol on a measure of behavioral inhibitionin humans

Little is known about the acute effects of psychoactive drugs on impulsivit y and decision making in humans. This study examined the effects of d-amphe tamine (AMP; 10 and 20 mg; N = 20) and ethanol (EtOH; 0.2, 0.4, and 0.8 g/k g; N = 17) on the stop task, a putative measure of behavioral inhibition an d impulsivity in healthy human volunteers. The stop task provides a measure of the reaction time (RT) needed to inhibit a response (Stop RT [SRT]), re lative to the time taken to execute a simple response (Go RT [GRT]). Health y volunteers performed the stop task before and after receiving one of the drugs. AMP decreased SRT-that is, improved inhibition-only in participants with slow baseline SRTs. EtOH increased SRTs-that is, impaired inhibition-a t doses that did not affect GRTs. These results suggest that AMP and EtOH h ave specific and distinctive effects on the ability to inhibit responses. I mpairment in the ability to inhibit responses is thought to reflect a certa in form of impulsivity.