What exactly will medications do for a person with ADHD

I have a thought that expectations of the benefits of ADHD medication may be too high.  Maybe not so much for the non-ADHD spouse, but for the person with a later-in-life diagnosis of ADHD.  

A person with near-sightedness can wear a pair of glasses or contacts to 'improve' their vision.  At days end, they remove the glasses or contacts, and obviously those things did not 'fix' their vision.

I think if we had a clear list of specifically what the medication will do, than it may be easier to understand if the the medication is beneficial or not.

Just wondering,