Open-label, Single-dose Trial to Assess the Pharmacokinetics of Centanafadine Extended-release Capsules in Pediatric Participants With Attention-deficit Hyperactivity Disorder (ADHD)

Inclusion Criteria: * Written informed consent obtained from a legally acceptable representative and assent obtained from the participant prior to the initiation of any trial-related procedures. * Male or female participants 9 to 12 years of age, inclusive, at the time of informed consent. * Participants with documented history of ADHD and confirmation of an ADHD prescription medication. * Participant is judged by the investigator to be clinically stable and has not had any psychiatric hospitalizations within the past 12 weeks. Exclusion Criteria: * Participants with a history of intellectual disability as determined by at least 1 of the following: intelligence quotient (IQ) \< 70, or clinical evidence, or a social or school history that is suggestive of an intellectual disability. * Participants who have any of the following: * Significant risk of committing suicide based on history * Current suicidal behavior * Imminent risk of injury to self * Active suicidal ideation * Any lifetime history of suicidal behavior detected by the "Baseline/Screening" version of the Columbia-Suicide Severity Rating Scale (C-SSRS). * Participants with a lifetime history of a substance use disorder (as determined by Diagnostic and Statistical Manual of Mental Disorders, 5th Edition \[DSM-5\] criteria), or current substance misuse including alcohol and benzodiazepines, but excluding caffeine and nicotine. * Participants with hypothyroidism or hyperthyroidism or an abnormal result for free thyroxine (T4) at screening. * Participants who currently have clinically significant neurological, dermatological, hepatic, renal, metabolic, hematological, immunological, cardiovascular, pulmonary, or gastrointestinal disorders. * Participants with insulin-dependent diabetes mellitus. * Participants with epilepsy or a history of seizures or a history of severe head trauma or cerebrovascular disease. * Any major surgery within 30 days prior to dosing with the investigational medicinal product (IMP). * Any history of significant bleeding or hemorrhagic tendencies. * Blood transfusion within 30 days prior to dosing with IMP. * Participants with a positive drug screen for cocaine, marijuana (even if by prescription), or other illicit drugs, or alcohol, are excluded and may not be retested or rescreened. * Participants who have a supine or standing diastolic blood pressure, after resting for at least 5 minutes ≥ 95 mmHg. * Participants who participated in a clinical trial and were exposed to IMP within the last 30 days prior to screening or who participated in more than 2 interventional clinical trials within the past year. * Participants with a history of true allergic response to a medication or a history of dermatologic adverse reactions or anaphylaxis secondary to drug exposure. * Participants who do not tolerate venipuncture or have poor venous access that would cause difficulty when collecting blood samples. * Relatives of the trial site employees cannot participate in the trial.