Individual differences in humans responding under a cocaine discrimination procedure: discriminators versus...

Twenty-six cocaine-abusing volunteers were trained to discriminate cocaine (80 mg/70 kg, p.o.) from placebo. On the basis of a discrimination acquisition criterion (i.e., >80% drug-appropriate responding for 4 consecutive sessions within 8-10 sessions), 18 participants were classified as discriminators (Ds) and 8 as nondiscriminators (NDs). Relative to Ds, NDs reported a greater amount of cocaine use per time. During the training phase, NDs showed significantly lower ratings than Ds on a stimulant ratings scale, regardless of the training drug condition. During the test-of-acquisition phase, cocaine-induced increases in scores on ratings of drug strength, anxious-nervous and cocaine high, as well as on a euphoria ratings scale, were significantly greater in Ds than NDs, relative to placebo. These results suggest that drug use history, general arousal level, and drug sensitivity may be important variables influencing the acquisition of cocaine versus placebo discrimination in cocaine abusers.