How do attention deficit disorder drugs work based upon neurotransmitter activity in the brain?

Dopamine. The stimulant medications (like Adderall (dextroamphetamine and racemic amphetamine) and ritalin), which are the best meds for adhd, work primarily by increasing the neurotransmitter Dopamine in a part of the brain called the prefrontal cortex, which controls executive functioning, which lets you plan, shift from task to task, and focus. People with adhd have a shortage of Dopamine in this area.
Still under stiudy. Most medications that work for adhd have the effect of increasing dopamin, a brain neurotransmitter that is closely linked to the reward system. However, details as to why increasing Dopamine activity seems to be so helpful with this disorder remain to be clarified--and it still isn't clear at all that the problem of adhd itself is a result of poor functioning of the dopamin system.