Inclusion Criteria:  Boys aged ≤ 10 years and girls aged ≤ 9 years. Children treated with stimulants medications for ADHD for at list 3 months. Prepubertal -Tanner stage 1 (gonadarche) (boys: testicular volume < 4, girls: breast at Tanner stage 1) Normal weight status: BMI-SDS ≤ 85th percentile for age and gender according to the CDC 2000 growth charts Signing inform consent forms  Exclusion Criteria:  Diagnosis of GH Deficiency or treatment with GH Any known chronic disease or dysmorphic syndrome including bone diseases, organic brain diseases, neurological disease, past or current malignancy, chronic cardiac, renal or pulmonary problems Any known gastrointestinal disease including malabsorption Any known organic reason for growth retardation Milk allergy. Any chronic treatment with additional medication beside stimulants that might affect appetite, weight, or growth (for example SSRI's).