UNIT-PRICE ANALYSIS OF OPIOID CONSUMPTION BY MONKEYS RESPONDING UNDERA PROGRESSIVE-RATIO SCHEDULE OF DRUG INJECTION

Several reports have indicated that drug consumption in self-administr ation procedures is a function of the ratio of the instrumental requir ement to the dose of drug, a quantity termed unit price. We evaluated three predictions from this unit-price model in a reanalysis of data o n opioid self-administration in rhesus monkeys responding under a prog ressive-ratio schedule (Hoffmeister, 1979). We evaluated whether consu mption was inversely related to unit price, and compared the goodness of fit of an equation devised by Hursh, Raslear, Shurtleff, Bauman, an d Simmons (1988) to that of a linear model predicting consumption as a function of dose. We also tested whether consumption was constant whe n the same unit price was comprised of different combinations of dose and instrumental requirement. Consumption declined overall as unit pri ce increased. The equation devised by Hursh et al. and the linear mode l based on dose fit the data equally well. Drug consumption was not un iform at a given unit price. The analyses suggest limits on the unit-p rice model as a characterization of drug consumption.