Objective:Serdexmethylphenidate/dexmethylphenidate (SDX/d-MPH) is approved for the treatment of patients aged ≥6 years with attention-deficit/hyperactivity disorder (ADHD). A 12-month, open-label safety study with SDX/d-MPH in children with ADHD showed that SDX/d-MPH was well tolerated and comparable with other methylphenidate products. In thispost hocanalysis of the 12-month study, the objective was to characterize the effect of SDX/d-MPH on growth in children with ADHD over 12 months.Methods:This was apost hocanalysis of a dose-optimized, open-label, phase 3 safety study of SDX/d-MPH in children aged 6–12 years with ADHD (NCT03460652). Weight and heightZ-score analyses were conducted.Z-score change from baseline was calculated based on the baseline values for the subjects remaining in the study at the observation time point.Results:Subjects (N= 238) from the treatment-phase safety population included all enrolled subjects who received ≥1 dose of study drug and had ≥1 postdose safety assessment. During treatment, the mean weight and heightZ-scores decreased over time from their respective baselines. At the 12-month time point, mean (standard deviation [SD])Z-score changes from baseline for weight and height for the subjects remaining in the study were −0.20 (0.50) and −0.21 (0.39), respectively; however, these mean changes in Z-scores were not clinically significant (change <0.5 SD). Long-term treatment with SDX/d-MPH was associated with modest reductions in expected weight and lower-than-expected increases in height: effects that plateaued or diminished later in treatment.Conclusion:The overall effects of SDX/d-MPH on growth velocity (the change in weight and height from one time point to the next) were minimal, and the range of changes was not considered clinically significant.ClinicalTrials.govidentifier: NCT03460652.