Behavioral economic analysis of opioid consumption in heroin-dependent individuals: effects of unit price and pre-session drug supply.

Behavioral economic analysis has been used to investigate factors underlying drug consumption in laboratory animals and, increasingly, in human drug abusers. However, there are few studies in heroin abusers, especially those who are not in treatment; such studies may be valuable for understanding the mechanisms of persistent drug use. This study investigated effects of unit price (UP) and pre-session supply of hydromorphone (HYD) on choice and consumption of HYD. Heroin-dependent research volunteers (n=13) stabilized on buprenorphine 8 mg/day completed this eight-session inpatient study. In sessions 1-2, participants sampled two total HYD doses (12 and 24 mg IM) that could be earned in later sessions. In each of the final six sessions, volunteers were given access to a 12-trial choice progressive ratio schedule lasting 3h. On each trial, volunteers could earn a HYD unit dose (1 or 2 mg, for a maximum of 12 or 24 mg, respectively) or money (US dollars 2, for a maximum of US dollars 24). Fixed ratio requirements increased exponentially, generating 24 unit prices for behavioral economic analysis. Before some choice sessions, volunteers could choose (FR 1) to receive extra HYD (12 or 24 mg; at 0915), whereas on other days no supplement was available. HYD choice and peak responding (breakpoint, O(max)) measures increased with unit dose, decreased with pre-session supplements, and were greater among volunteers who used cocaine prior to the experiment. Taking pre-session supplements decreased P(max) and made group-percent HYD consumption more demand-elastic. Consumption was functionally equivalent at differing FR/unit dose combinations. Thus, opioid demand in heroin-dependent individuals not in treatment is a function of drug supply, unit price, and cocaine use.