Administration of d-amphetamine produced typical effects on mood, but none of the DRD2 loci included in the study were associated with mood responses to the drug. The drug did not significantly alter stop RT, F(3, 264) = 1.6, p = .18; or go RT, F(3, 264) = 0.23, p = .88. However, the drug did influence stop RT when we stratified on the genotype of SNP rs12364283; for Dose × Genotype, F(3, 258) = 4.0, p = .008 (Figure 2A). None of the remaining SNPs showed a statistically significant differential pattern of response to d-amphetamine. Post hoc comparisons indicated that d-amphetamine decreased stop RT in the A/A group but increased stop RT in the combined A/G + G/G genotype. In comparison with the placebo condition, d-amphetamine decreased stop RT in the 5-mg (p ≤ .05), 10-mg (p ≤.001), and 20-mg (p ≤.05) conditions in the A/A group. However, in the combined A/G + G/G genotype, 10-mg d-amphetamine (p ≤.05) increased stop RT in comparison with the placebo. Administration of other doses of d-amphetamine did not produce results that were different
