Adderall XR 20mg is a combination medication used to treat attention deficit hyperactivity disorder – ADHD. It works by changing the amounts of certain natural substances in the brain. Amphetamine/dextroamphetamine belongs to a class of drugs known as stimulants. It can help increase your ability to pay attention, stay focused on an activity, and control behaviour problems. It may also help you to organise your tasks and improve listening skills.