To summarize, this retrospective study in children with ADHD achieved the following key findings: (1) the CYP2D6 genotype was identified as the most significant factor affecting the systemic exposure to atomoxetine; (2) the clinical efficacy and tolerability of atomoxetine therapy were associated with the CYP2D6 genotype; (3) the results of this study provided evidence for recommending specific treatment strategies based on CYP2D6 genotype and plasma atomoxetine concentration monitoring. The gene discussed is CYP2D6; the disease is attention deficit-hyperactivity disorder.