**Abstract:**
Some people are more willing to make impulsive, risky, or costly choices than others, which has been assumed to be strongly associated with individual differences in dopamine (DA) function. In two studies using PET imaging, one empirical (Study 1: N=144) and one meta-analytic (Study 2: N=332), we sought to characterize associations between individual differences in DA and time, probability, and physical effort discounting in human adults. Study 1 demonstrated that individual differences in DA D2-like receptors were not reliably associated with time, probability, or physical effort discounting of monetary rewards in healthy humans. Meta-analytic results from Study 2 corroborated our empirical finding and demonstrated that the nature of associations between individual differences in DA and reward discounting depended on clinical features linked to disrupted DA function. Higher DA was associated with higher discounting in hypodopaminergic clinical groups whereas the opposite was observed in hyperdopaminergic groups where lower DA was associated with higher discounting. Together the results suggest that trait differences in discounting in healthy adults do not appear to be strongly associated with individual differences in D2-like receptors. The difference in meta-analytic correlation effects between healthy controls and individuals with psychopathology suggests that individual difference findings related to DA and reward discounting in clinical samples may not be reliably generalized to healthy controls, and vice-versa.
