Reinforcing and subjective effects of diazepam in nondrug-abusing volunteers.

Preference for diazepam was assessed in 18 light and 12 moderate social drinkers using a cumulative dosing procedure. The 7-session procedure consisted of: 1) four sampling sessions, during which participants ingested color-coded capsules containing either diazepam (five 4-mg capsules administered at 30-min intervals; total dose 20 mg) or placebo, and 2) three choice sessions, during which they could ingest up to 7 capsules of their preferred color of capsule, each separated by 30 min. Subjective (mood) and behavioral (performance) measures were obtained throughout the 4-hour sessions. The light social drinkers chose diazepam over placebo on 66% of the choice sessions, and ingested a mean dose per session of about 16 mg. The moderate drinkers chose diazepam on 100% of the choice sessions, and ingested an average dose of 25 mg per session. Diazepam produced sedation in both groups, but in the moderate drinkers it also increased measures of subjective effects suggestive of "euphoria." The results indicate that diazepam can serve as a positive reinforcer under laboratory conditions in nondrug-abusing individuals who are moderate users of alcohol and other drugs. Greater reinforcing efficacy may be indicative of higher risk of abuse. The results illustrate the usefulness of the cumulative dosing procedure to measure both drug preference and dose preference.