This study is a cross-over trial, design to determine the efficacy and safety of generic and original prolong-release methylphenidate (PR-MPH) in children with ADHD who had received immediate-release methylphenidate treatment

This 4 weeks cross-over study will recruit 78 children, aged 6 to 12 years, with ADHD. They will be randomized to receive generic or original PR-MPH for 4 weeks and then switch to another brand for 4 weeks. Swanson, Nolan and Pelham parent rating scale is used to measure the primary outcome.

Inclusion Criteria:

• Ages 6 to 12 years
• Diagnosis of ADHD according to DSM-5 of ICD-10
• Patient who receiving a stable dose of IR-MPH for at least 4 weeks before screening
• Patient who has a stable clinical symptoms.
• Patients or their legal representatives provide informed consent prior to enrollment

Exclusion Criteria:

• Patients who present of a serious obstructive gastrointestinal disease
• Patients cannot swallow the whole tablet
• Patients with depression, schizophrenia, bipolar disorder, and 1-month substance use prior to study
• Patients who present of an unstable co-morbidity: anxiety, seizure, conduct disorder and oppositional defiant disorder
• Patients or patients' family have a history of poor compliance
• Patients who receiving monoamine oxidase inhibitors antidepressant or stop taking not more than 14 days
• Patients who receiving PR-MPH except stop taking more than 7 days
• Patients' parent has a family problem and currently treatment with family therapy or adjust medication