Pharmacokinetics of HLD200 in Children and Adolescents With ADHD

Inclusion Criteria: * Male and female adolescents (13-17 years) and children (6-12 years). * Previous diagnosis of ADHD and confirmation using the Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID). * ADHD symptoms controlled on a stable dose of ADHD medication. Subjects should be on MPH or have previous history of symptom control during treatment with MPH. * Physical examination free of clinically significant findings, unless deemed NCS by the Investigator and Medical Monitor; * Able to swallow treatment capsules; * Available for entire study period; * Provision of informed consent (from the parent\[s\] and/or legal representative\[s\]) and assent (from the subject); and * Female subjects of childbearing potential (i.e., post-menarche) required to have a negative result on urine pregnancy testing (and will be given specific instructions on avoiding pregnancy during trial) Exclusion Criteria: * Any known history or presence of significant cardiovascular, pulmonary, hepatic, renal, hematologic, gastrointestinal, endocrine, immunologic, dermatologic, neurologic, ophthalmologic disease, unless deemed NCS by the Investigator and the Medical Monitor; * Presence of any significant physical or organ abnormality; * Any illness during the 4 weeks before this study, unless deemed NCS by the Investigator and the Clinical and/or Medical Monitor; * Severe comorbid psychiatric diagnosis that may affect subject safety or confound results (e.g., psychosis, bipolar disorder); * Known history of moderate to severe asthma; * Known history of severe allergic reaction (including drugs, food, insect bites, environmental allergens); * Known history of seizures (except febrile seizures prior to age 5), anorexia nervosa, bulimia or current diagnosis or family history of Tourette's disorder; * Subject who are severely underweight or overweight. * Clinical value outside of the acceptable ranges, unless deemed NCS significant per the Investigator; * Positive history for hepatitis B, hepatitis C and Human Immunodeficiency Virus (HIV); * Positive screening for illicit drug use, and/or current health conditions or use of medications that might confound the results of the study or increase risk to the subject; * Use of prescription medications (except ADHD medications) within 7 days and over-the counter medications (except birth control) within the 3 days preceding study enrollment, unless deemed acceptable by the Investigator and Clinical and/or Medical Monitor; * Blood draws of 50 ml to 249 ml within the 30 days, 250 ml to 449 ml within the 45 days and ≥ 450 ml within the 60 days preceding study enrollment; * Participation in clinical trial with an investigational drug within the 30 days preceding study enrollment; * Intolerance to venipuncture; and * Current suicidal ideation or history of suicidality determined as a significant finding on the Columbia-Suicide Severity Rating Scale (C-SSRS) by the investigator (Baseline C-SSRS for adolescents; Pediatric Baseline C-SSRS for children).