Therefore, this study aimed to address the above‐mentioned issues by examining the availability of DAT in drug‐naive adults with ADHD compared with healthy controls (HCs) using SPECT with iodine‐123‐β‐carbomethoxy‐3β‐(4‐iodophenyltropane) (I‐123butter CIT) as a tracer. The gene discussed is SLC6A3; the disease is attention deficit-hyperactivity disorder.