The preferred drug for treating attention deficit hyperactivity disorder in a 6 year old boy, whose father has a history of substance abuse:-

Attention deficit hyperactivity disorder - Boys > girls Age : 5 to 12 years Clinical features Inattention Hyperactivity Impulsiveness - often has troubles waiting one's turn Rx Stimulants - Methylphenidate (DOC) Dexmethylphenidate Non stimulants - Atomoxetine- If history of substance abuse