system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are people with ADHD given stimulants? Don't they make you more hyper, like coffee does?
gpt
ADHD, put simply, is a deficiency of Dopamine. Dopamine tells the brain which activities are important. Normally certain behaviours cause a rise in dopamine levels to reward or encourage an action.  If the brain sees no point in doing something, no dopamine gets released. 

This system thus points our attention to desirable actions. A lack of dopamine consequently leads to a lack of directed attention. Everything is categorised as equally important and no filter is applied to new information reaching the brain. However the brain tries to get a dopamine hit and seeks new stimuli without success. 

Stimulants either lead to a direct release of dopamine(amphetamines) or block the processes concerned with breaking down dopamine(Cocaine, Ritalin). This allows people with ADHD to focus on things as their brain no longer seeks new information to trigger dopamine release as enough dopamine is avaliable. The brain is no longer restless by working on finding dopamine triggers all the time, allowing it to rest ironically.