Efficacy of GXR as Adjunctive Therapy With Psycho-stimulant on Executive Function in Children With ADHD

Inclusion Criteria: 1. Male or female patient aged 6 to 12 years at the time of consent/assent and to then of study. A patient who would turn 13 before the end of the study cannot be enrolled 2. Patient's parent or legally authorized representative (LAR) must provide signed informed consent before any study-related procedures are completed. 3. Patient meets the diagnostic standard manual-5 criteria for a primary diagnosis of ADHD, combined sub-type, hyperactive/impulsive sub-type, or inattentive sub-type 4. Patient is currently on a stable stimulant regimen but whose EF is suboptimal. Suboptimal EF is defined as a global executive composite t-score greater than 65 (\>1.5 SD from mean) on the BRIEF-P questionnaire at screening. 5. Patient who is currently and is expected to remain on a stable stimulant regimen throughout the study. A stable stimulant regimen is defined as: •No significant change in dose or dosing frequency within the past 30 days prior to screening and stimulant is felt to be optimized by the investigator. 6. Patient is functioning at an age-appropriate level intellectually, as judged by the Investigator. 7. Patient is able to swallow intact tablets. 8. Patient has sitting blood pressure (BP) measurement within the 95th percentile for age, sex, and height (see Blood Pressure Levels for Boys and Girls by Age and Height Percentile 9. Patient and parent/LAR understand, are willing, able, and likely to fully comply with the study procedures and restrictions defined in this protocol. Exclusion Criteria: 1. Patient has a current, controlled (requiring a prohibited medication or behavioural modification program) or uncontrolled, co-morbid psychiatric diagnosis \[except oppositional defiant disorder (ODD)\], including any severe co-morbid Axis II disorders or severe Axis I disorders such as post-traumatic stress disorder (PTSD), bipolar illness, psychosis, pervasive developmental disorder, obsessive-compulsive disorder (OCD), substance abuse disorder, or other symptomatic manifestations or lifetime history of bipolar illness, psychosis or conduct disorder. 2. Patient has any condition or illness which, in the opinion of the Investigator, represents an inappropriate risk to the patient and/or could confound the interpretation of the study. Mild stable asthma treated without the use of beta-2 agonist is not exclusionary. 3. Patient has a known personal history, or presence, of structural cardiac abnormalities, cardiovascular or cerebrovascular disease, serious heart rhythm abnormalities, syncope, tachycardia, cardiac conduction problems (e.g., clinically significant heart block or QT interval prolongation: QTc \>0.44 seconds), exercise-related cardiac events including syncope and pre-syncope, or clinically significant bradycardia. 4. Patient has a known family history (in siblings, parents, and/or grand-parents) of sudden cardiac death, ventricular arrhythmia, or QT prolongation (QTc \>0.44 seconds). 5. Patient has a known history of hypertension (see Blood Pressure Levels for Boys and Girls by Age and Height Percentile 6. Patient has glaucoma. 7. Patient has a history of a seizure disorder (other than a simple childhood febrile seizure). 8. Patient has renal or hepatic insufficiency 9. Patient is currently using prohibited medication. 10. Patient has taken another investigational product within 30 days prior to the Enrolment Visit. 11. Patient has a known or suspected allergy, hypersensitivity, or clinically significant intolerance to guanfacine hydrochloride or any of its active ingredients or patient is taking other products containing guanfacine. 12. History of adverse event or failure to respond (lack of efficacy) to an adequate trial of an alpha-agonist. 13. Patient is female and is pregnant or currently lactating. 14. Patient is currently considered a suicide risk in the opinion of the Investigator, has previously made a suicide attempt, or has a prior history of, or is currently demonstrating active suicide ideation. Patients with intermittent passive suicidal ideation are not necessarily excluded based on the assessment of the Investigator.