(A) Regression plots depicting the association of age and subjective drug effects with striatal dopamine D1-like dopamine receptor (D1R), D2R, and methylphenidate-induced (MP-induced) dopamine increases. All analyses were controlled for BMI and sex. (B) Negative association between subjective drug effects and age. To quantify total effects of the drug across the session, we calculated area under the curve (AUC) for all time points (every 5 minutes, from –5 minutes to 120 minutes after administration of MP) and subtracted the AUC between the MP and placebo (PLA) sessions to get one estimate of the cumulative drug effects per participant. Thus, a negative value for “feel drug effects” indicates a greater subjective response to PLA than MP. (C) A selective role for D1R but not D2R in the subjective effects of MP. Nucleus accumbens D1R but not D2R availability was significantly associated with subjective drug effects. The difference in regression slopes was significant (z = 3.699, P < 0.001). (D) D1R availability in the nucleus accumbens mediates the negative association between age and subjective drug effects. DVR, distribution volume ratio. *P < 0.05; ***P < 0.001.