Further studies on the discriminative stimulus effects of diazepam in humans

Twelve normal humans were trained to discriminate between 10mg diazepam (DZ) and placebo. Subjects reported to the laboratory for a total of 23 sessions. They filled out subjective effects questionnaires and ingested a capsule. They were then free to leave but filled out questionnaires 1, 3 and 6h later. During the first four sessions, the capsule was identified by letter code prior to ingestion. During the next seven sessions, the procedure was the same but the capsule was not identified. Six hours after receiving the capsule, subjects telephoned the experimenter to report their identification. When correct, they received a monetary bonus. Phase 3 consisted of 12 sessions including six additional training sessions. During the remaining sessions, subjects received capsules that contained test drugs. Seven of 10 subjects that completed the study were reliable discriminators. During phase 3, most subjects identified 25 and 50mg tripelennamine, 0.125mg triazolam, and 5mg buspirone as placebo and these drugs produced few changes in mood. Triazolam at a dose of 0.25mg was identified as DZ by all subjects whereas 10mg buspirone was identified as DZ by 71%. DZ and 0.25mg triazolam produced similar time-related changes on several subjective effects measures. Ten mg buspirone also produced changes in mood that were similar to those of DZ but usually of smaller magnitude and shorter duration.