A Study of TAK-503 in Children and Teenagers With Attention Deficit Hyperactivity Disorder (ADHD)

This study will be conducted in two parts Part A and Part B. Part A is a double-blinded, double-dummy, placebo-controlled study with an atomoxetine arm as an active reference to TAK-503. Eligible participants with ADHD will be randomized in a 1:1:1 ratio among TAK-503, atomoxetine, and placebo treatment arms up to 49 weeks of double-blinded treatment. Upon completion of Part A, participants will roll over to Part B directly as per the study protocol directions for an additional 52 weeks of open-label TAK-503 treatment.