Discriminative-stimulus effects of zolpidem, triazolam, pentobarbital, and caffeine in zolpidem-trained humans

Six non-drug-abusing humans were trained to discriminate 15 mg zolpidem in the present experiment. After participants acquired discrimination, a range of doses of zolpidem (2.5-15.0 mg), triazolam (0.0625-0.3750 mg), pentobarbital (25-150 mg), caffeine (100-600 mg), and placebo were tested to determine whether they shared discriminative-stimulus effects with 15 mg zolpidem. The participant-rated and performance-impairing effects of zolpidem, triazolam, pentobarbital, and caffeine were assessed concurrently. Triazolam and pentobarbital dose dependently increased zolpidem-appropriate responding. Caffeine occasioned low levels of zolpidem-appropriate responding. Zolpidem, triazolam, and pentobarbital, but not caffeine, generally produced a similar constellation of participant-rated drug effects (e.g., increased scores for the Pentobarbital, Chlorpromazine, and Alcohol Group subscale on the Addiction Research Center Inventory) and dose dependently impaired performance. These results suggest that humans can reliably discriminate zolpidem. Despite its unique benzodiazepine-receptor binding profile, the discriminative-stimulus, participant-rated, and performance-impairing effects of zolpidem are similar to those of the barbiturates and benzodiazepines.