Human drug self-administration: Double-blind comparison of pentobarbital, diazepam, chlorpromazine and placebo

In a residential hospital ward setting pentobarbital (30 or 90 mg/ingestion), diazepam (10 or 20 mg/ingestion), chlorpromazine (25 or 50 mg/ingestion) or placebo were made available for oral ingestion under double-blind conditions to volunteer human subjects with documented histories of sedative abuse. A drug was made available for 5 to 15 consecutive days and the order of exposure to different drugs was mixed. A maximum of 10 ingestions were available during a 7.5 hr session each day. On the 1st day of drug availability ingestions were available upon request of the subject, provided that 15 min had elapsed since the last dose was dispensed. After the 1st day subjects were required to obtain each ingestion of drug by riding a stationary exercise bicycle for 15 min. Although all three drugs produced subjective effects and observable signs of sedative intoxication, the drugs were associated with different amounts of self-administration. With the exception of one idiosyncratic subject, chlorpromazine was similar to placebo in that it did not maintain self-administration. Both diazepam and pentobarbital maintained self-administration with the higher dose of each associated with higher average levels of self-administration than the lower dose. The high dose of pentobarbital was associated with higher levels of self-administration than was the high dose of diazepam. These results generally correspond to both the results of animal drug self-administration studies as well as clinical information about the abuse of these drugs.