An amphetamine-challenge PET study found a larger striatal dopamine-related response in adults with ADHD than in controls. Cognitive testing occurred separately without the drug, so the study should not be described as directly showing amphetamine-induced improvement or worsening of inhibition.
Cherkasova and colleagues studied 15 treatment-free men with ADHD and 18 healthy male controls. Each underwent PET after placebo and oral d-amphetamine, 0.3 mg/kg, in a double-blind, counterbalanced design.
The radioligand was carbon-11 raclopride. A separate drug-free session assessed neurocognitive function. Keeping those sessions distinct is essential when interpreting correlations between imaging and performance.
The ADHD group showed greater amphetamine-associated decreases in striatal raclopride binding. The researchers interpreted that displacement as evidence consistent with greater dopamine release. The ADHD participants also performed more poorly on response-inhibition measures.
Across groups, larger binding changes were associated with poorer inhibition and more ADHD symptoms. That is an association between challenge responsivity and separately measured function, not proof that the challenge caused the cognitive deficit.
Raclopride binding reflects radioligand behavior at dopamine receptors under the imaging conditions. It is not an amphetamine concentration in blood or a direct chemical measurement of every aspect of dopamine signaling.
The authors noted that their findings contrasted with a previous study. The direction and meaning of dopamine-related differences therefore should not be presented as a settled universal feature of ADHD.
The modest sample consisted entirely of men and excluded important comorbidities. It did not establish predictive accuracy for selecting treatment, diagnosing ADHD in a new patient or forecasting individual adverse responses.
The study is useful for testing models of dopamine responsivity. It cannot substitute for an individual clinical assessment or establish whether someone with amphetamine detected in a specimen was impaired during a separate event.
Related reading: COMT genotype and attention effects.