This project will evaluate the effectiveness of Methylphenidate versus Guanfacine in treating Attention-Deficit/Hyperactivity Disorder (ADHD) in children aged 3 through 5 years (inclusive), as measured by clinician rating of global improvement.

Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most common neurodevelopmental disorders, affecting 2-3% of U.S. children under 6 (also called preschool-age children. Preschool Attention-Deficit/Hyperactivity Disorder is linked to difficulties in school or daycare, with friendships and family relationships, and accidental injuries. Behavioral therapy is recommended as the first step in treating preschool-age Attention-Deficit/Hyperactivity Disorder. However, for some children, behavior therapy is not enough. For these children, medication may also be needed to treat their Attention-Deficit/Hyperactivity Disorder.

The most common medications used to treat Attention-Deficit/Hyperactivity Disorder in preschool-age children are Methylphenidate and Guanfacine. Currently, there is not enough research to help families and doctors choose between these two medications when treating this age group. This research study will fill this gap by directly comparing the benefits and side effects of Methylphenidate and Guanfacine for treating Attention-Deficit/Hyperactivity Disorder in this age group, giving families and clinicians the information they need to make evidence-based treatment choices.

The main goal of this study is to compare the effectiveness of Methylphenidate and Guanfacine in children ages 3-5, focusing on clinically meaningful improvement in overall functioning. Clinicians will measure the child's improvement using the Clinical Global Impressions scale.

There are also secondary goals in this study. One of those secondary goals is to understand how acceptable and tolerable each of these medications is, from the family perspective and the clinician perspective. This will be learned in a few ways. It will be measured through how long participants choose to stay on the medication and through surveys from caregivers about medication side effects (Pittsburgh Side Effect Rating Scale) at the beginning of the study and again 4, 8, 12, and 16 weeks after starting medication.

The other secondary goals are to understand if medication choice impacts a child and their family in other ways (e.g. behavioral symptoms, parenting stress) and learn about any factors that may influence a child's response to medication (e.g. age, initial symptoms). This information will primarily come from caregiver surveys (Parenting Stress Index, Vanderbilt Attention-Deficit/Hyperactivity Disorder Parent Rating Scales, Affective Reactivity Index). If the caregiver agrees, and the child has a teacher, their teacher will also complete surveys (Vanderbilt Attention-Deficit/Hyperactivity Disorder Teacher Rating Scales, Affective Reactivity Index). The Vanderbilt Attention-Deficit/Hyperactivity Disorder Rating Scales are completed at the beginning of the study and again 4, 8, 12, and 16 weeks after starting medication. The Parenting Stress Index and Affective Reactivity Index are completed at the beginning of the study and again 8 and 16 weeks after starting medication.

Caregivers and their child will be required to attend 3 in person visits (before starting medication and again 8 weeks and 16 weeks after starting medication. At these visits, a study doctor will measure the child's height, weight, blood pressure, and heart rate to make sure that the medication is safe to start or continue. The other 3 visits with study doctors can be in-person or online. If a teacher is completing study surveys, they will all be available through a secure, online platform.

This study uses a randomization to compare the effectiveness of Methylphenidate and Guanfacine in preschool-age children with Attention-Deficit/Hyperactivity Disorder, including how side effects may differ.

This study aims to provide evidence-based guidance on using Methylphenidate and Guanfacine in treating Attention-Deficit/Hyperactivity Disorder in preschool-age children. Evidence about each medicine's effectiveness in this age group will help families and clinicians make more informed decisions when treating preschool-age children with Attention-Deficit/Hyperactivity Disorder.

This research study is being co-designed with parents, clinicians, and health systems stakeholders. Working with these stakeholders helps ensure that the research will be practical for families, clinicians, and health systems. Caregivers of children with Attention-Deficit/Hyperactivity Disorder, who are 3-5 (inclusive) will be recruited to participate. Across the United States, 5 total sites will participate to enroll a total of 370 children in this study.

Inclusion Criteria:

1. Males or females 3 to 5 years of age, inclusive (e.g. children age 5 years, 11 months are eligible).
2. Child has a confirmed diagnosis of moderate or severe Attention-Deficit/Hyperactivity Disorder (diagnostic code: F90.9) based on Diagnostic and Statistical Manual of Mental Disorders - 5th Edition (DSM-5) criteria, review of supportive evidence (caregiver interview, behavioral observations, Vanderbilt Attention-Deficit/Hyperactivity Disorder Rating Scale results, any school or daycare information provided by caregiver).
3. Clinician-rated Clinical Global Impairment-Severity (see description below) rating of ≥4 (denoting moderate or greater impairment due to their Attention-Deficit/Hyperactivity Disorder symptoms).
4. The child's clinician and caretakers have decided on or are considering initiating drug therapy (with either Methylphenidate or Guanfacine).
5. Primary language is English or Spanish.

Exclusion Criteria:

1. History of taking Methylphenidate or Guanfacine. Prior use of other Attention-Deficit/Hyperactivity Disorder medications or other psychotropic medications is allowed.
2. Current use of other Attention-Deficit/Hyperactivity Disorder medications (e.g., amphetamines), other psychotropic medications (e.g., atypical antipsychotics or serotonin reuptake inhibitors), or centrally active depressants (such as phenothiazines, barbiturates, or benzodiazepines)
3. Electronic Health Record documentation of moderate to severe global developmental delay (F88) or intellectual disability (F70), or a score of <55 on the Vineland Adaptive Behavior Scales-3.
4. Medical contraindications to taking Methylphenidate or Guanfacine, including cardiac risk factors (e.g. known structural cardiac abnormalities, cardiomyopathy, serious cardiac arrhythmias, coronary artery disease, or other serious cardiac disease), increased intraocular pressure, glaucoma, verbal tics, Tourette's Syndrome, psychosis

At this time, we do not plan to share individual participant data from this study. Our Institutional Review Board approval is contingent upon maintaining participant privacy and confidentiality, and sharing individual-level data would not be consistent with these requirements. While we may share aggregated, de-identified summary findings in publications or presentations, we cannot share any data that could potentially be linked back to individual participants. Only summary-level results will be made publicly available through publications and ClinicalTrials.gov.