Delay discounting in current and former marijuana-dependent individuals

Abstract

Studies have found that a variety of drug-dependent groups discount delayed rewards more than matched controls. This study compared delay discounting for a hypothetical $1,000 reward among dependent marijuana users, former dependent marijuana users, and matched controls. Discounting of marijuana was also assessed in the currently marijuana-dependent group. No significant differences in discounting were detected among the groups; however, currently dependent users showed a trend to discount money more than the other 2 groups. Within the dependent marijuana group, marijuana was discounted more than money, and discounting for money and marijuana was significantly and positively correlated. Regression analyses indicated that delay discounting was more closely associated with tobacco use than marijuana use. A variety of questionnaires were also administered, including impulsivity questionnaires. Dependent marijuana users scored as significantly more impulsive on the Impulsiveness subscale of the Eysenck Impulsiveness-Venturesomeness-Empathy questionnaire than controls. However, the 3 groups did not significantly differ on several other personality questionnaires, including the Barratt Impulsivity Scale-11. The Stanford Time Perception Inventory Present-Fatalistic subscale was positively correlated with money and marijuana discounting, indicating that a greater sense of powerlessness over the future is related to greater delay discounting. Results suggest that current marijuana dependence may be associated with a trend toward increased delay discounting, but this effect size appears to be smaller for marijuana than for previously examined drugs.

Figure 1

Individual log-transformed k values and group means for all groups and both commodities studied. A higher transformed k value indicates increased delay discounting or more impulsivity.