Assessing pentobarbital preference in normal volunteers using a cumulative dosing procedure.

Preference for pentobarbital was assessed in 12 normal healthy volunteers using a seven-session cumulative dosing choice procedure. On the first four sessions subjects sampled the drug and a placebo, and on the last three sessions they chose the substance they preferred. During each of the sampling sessions they ingested, at 30-min intervals, five capsules containing either pentobarbital (30 mg per dose) or placebo. During the choice sessions subjects first chose which capsules they preferred to take (drug or placebo), and then took from one to seven of these capsules, separated by 30 min between ingestions. Self-report measures of subjective effects were obtained at regular intervals during each session. Subjects chose the pentobarbital-containing capsules on average 52% of choice sessions, and ingested an average total dose of 132 mg. Although the drug produced only modest, sedative-like subjective and behavioral effects and there was little evidence of euphoric effects in the group as a whole, individual differences in drug liking and choice were observed. The results are discussed in terms of variables that affect the reinforcing effects of pentobarbital in normal volunteers, and they are contrasted to previous findings using this procedure with other sedative drugs.