MJB ADHD · Static reading view · Interactive version
Status: sourced · Content checked 2026-10-06
Different studies point to different parts of the system, and some findings depend on medication history. ADHD is better described as several routes to a similar set of difficulties.
The simple version — "ADHD is low dopamine" — is too simple. Some studies find lower dopamine markers, some find higher, and some differences appear to be adaptations to treatment rather than causes.
In 53 unmedicated adults, dopamine transporter and D2/D3 receptor binding were lower in reward-pathway regions than in controls, and lower binding correlated with inattention.
R5Across nine imaging studies, transporter density was on average 14% higher in ADHD, but strongly dependent on prior stimulant exposure: lower in drug-naive people and higher in previously medicated people.
R6Heterogeneity is not a weakness of the ADHD concept. It is what you expect from a polygenic, developmental condition — and it predicts that people will differ in which medicine, dose and formulation suits them, which is what clinical experience shows.
Most ADHD-influencing genetic variants are shared with other psychiatric conditions, supporting overlapping mechanisms rather than a single dedicated pathway.
W5There are no validated subtypes that predict which medicine an individual will respond to.