According to our current understanding, symptoms of attention deficit/ hyperactivity disorder (ADHD) are produced by functional deficits in three of the brain’s dopaminergic pathways and possibly the prefrontal norepinephrine pathway. To correct these deficits, stimulants are effective because they target the action of dopamine (primary action) and norepinephrine (secondary action) and increase the activity associated with those neurotransmitters.