Choice between money and intranasal heroin in morphine-maintained humans

Abstract

Five morphine-maintained individuals participated in an inpatient study evaluating the effects of a monetary alternative ($10, $20, $40) on intranasal (i.n.) heroin (placebo, 12.5, 25, 50, 100 mg) self-administration, using a procedure in which subjects chose between money and heroin. Each money amount was tested in combination with each heroin dose. Subjects responded under a progressive-ratio schedule (PR 50, 100, ..., 2800); the PR value increased independently for each option. Subjective, performance, and physiological effects were also measured during each session. Heroin breakpoint values increased in a dose-related manner, relative to placebo, when $10 or $20 was available. In contrast, only the highest dose produced a heroin breakpoint value that was significantly different from placebo when $40 was available. Heroin also produced dose-related increases in several ratings of drug effect, including "I feel ..." "a good drug effect", "high", "mellow", and "stimulated". These effects were not significantly affected by the alternative money condition. These results demonstrated: (1) the dose-related reinforcing effects of i.n. heroin in opioid-dependent individuals; (2) that i.n. heroin self-administration can be modified by the availability of an alternative reinforcer (i.e. money); and (3) that self-reported drug effects can be differentiated from drug self-administration.