We plan to recruit 200 children and adolescents aged between 6 to 17 years old in two years. Those patients would receive clinical interview by child psychiatrists to diagnose as ADHD and to exclude mental retardation, major psychiatric disorders and medical disorders. Moreover, we excluded children who ever received ADHD medication treatment more than one year, or received medication in recent 30 days. Initial assessment includes collecting saliva sample, and complete questionnaires (SNAP-IV), clinical rating (CGI-S) and psychological test (CPT-II, WISC-IV, CANTAB). After 1 month methylphenidate treatment, we would evaluate SNAP-IV, CGI-S, CGI-I and Barkley Psychostimulants Side Effects Rating Scale. We also would collect saliva samples to perform appetite related gene phenotyping to see the association between medication side effect and polymorphism of appetite related genes.

Inclusion Criteria:

• Age range from 6 years old to17 years old
• Diagnosis of ADHD.

Exclusion Criteria:

• mental retardation.
• major psychiatric disorders
• major medical disorders.

Children and adolescents aged between 6 to 17 years old, diagnosed as ADHD, and recieved methylphenidate treatment.