Heroin choice depends on income level and economy type

Abstract

Rationale: In a previous study, investigating choice between heroin and a non-drug alternative in animals and reductions in income (i.e., choices/day) caused the percentage of income spent on heroin to progressively decrease. In contrast, another study found that humans with opioid use disorder spent the majority of their income on heroin even though they had little income. Comparison of these two studies suggests that the seemingly conflicting results could be explained by differences in the underlying economy types of the choice alternatives.

Objective: The present experiment tested the hypothesis that the effect of income changes on choice between heroin and a non-drug alternative depends on economy type.

Methods: Rats chose between heroin and saccharin under three income levels. For the Closed group, the choice session was the only opportunity to obtain these reinforcers. For the Heroin Open group and the Saccharin Open group, choice sessions were followed by 3-h periods of unlimited access to heroin or saccharin, respectively.

Results: As income decreased, the Closed and Heroin Open groups, but not the Saccharin Open group, spent an increasingly greater percentage of income on saccharin than on heroin. The Saccharin Open group, compared to the other groups, spent a greater percentage of income on heroin as income decreased.

Conclusions: Results confirm that the effects of income and economy type can interact and this may explain the apparently discrepant results of earlier studies. More generally, findings suggest that situations where heroin choice has little consequence for consumption of non-drug alternatives may promote heroin use.

Keywords: Behavioral economics; Choice; Economy type; Heroin; Income; Rats.

Figure 1.

Schematic diagram of procedure used during choice sessions for the three groups. All rats previously learned to lever press for saccharin and for heroin.

Figure 2.

Mean (± SEM) percentage of income spent on heroin (left panel) and saccharin (right panel) as a function of income level (inter-trial interval) for the Closed (filled circles), Heroin Open (triangles), and Saccharin Open (squares) groups (n = 12 for each group). Note that the Y-axis scales differs over panels.

Figure 3.

Mean (± SEM) numbers of heroin infusions (top panel), saccharin reinforcers (middle panel), and omissions (bottom panel) during choice sessions at each income level for the three groups. Note that the Y-axis scales differs over panels.

Figure 4.

The top panel shows the mean (± SEM) numbers of heroin infusions or saccharin reinforcers obtained by the Heroin Open group and the Saccharin Open group, respectively, during the 3-h post-choice-session period at each income level. The bottom panel shows the mean (± SEM) numbers of heroin infusions or saccharin reinforcers obtained by these groups during the 3-h post-choice-session period over the last 18 sessions of training regardless of income level.