A Trial Evaluating the Efficacy and Safety of HLD200 in Children With ADHD

Inclusion Criteria: * Male and female children (6-12 years at study entry) * Previous diagnosis of ADHD and confirmation using the Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID) * 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) * Female subjects of childbearing potential (i.e., post-menarche) required to have a negative result on urine pregnancy test (and will be given specific instructions for 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 * Presence of any significant physical or organ abnormality * Any illness during the 4 weeks before this study * Comorbid psychiatric diagnosis that may affect subject safety or confound results (e.g., psychosis, bipolar disorder) * Known history of severe asthma (in the opinion of the investigator) unless deemed currently controlled * Known history of severe allergic reaction to MPH * 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 (in the opinion of the Investigator) * Any clinical laboratory value outside of the acceptable ranges, unless deemed NCS significant per the Investigator * Positive history for hepatitis B, hepatitis C or 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 or Medical Monitor * Participation in clinical trial with an investigational drug within the 30 days preceding study enrollment * Current suicidal ideation or history of suicidality determined as a significant finding on the C-SSRS by the investigator (Baseline C-SSRS for adolescents; Pediatric Baseline C-SSRS for children).