tl;dr: Up to 80% of ADHD patients show circadian disruption, including evening chronotype, delayed melatonin onset (~90 min in adults), blunted cortisol rhythms, reduced pineal volume, and attenuated BMAL1/PER2 clock-gene expression. Interventions that advance circadian phase—low-dose melatonin, morning bright light therapy, behavioral sleep programs, and fixed wake times—have been shown to improve both sleep and ADHD symptoms, with bright light appearing especially effective in winter. The authors propose routine circadian screening and a behavioral-first chronotherapy pathway as adjuncts to standard ADHD treatment, though more stratified trials are needed to define responder phenotypes.