multiple sclerosis
"I was prescribed this medication to deal with the overwhelming fatigue that sometimes hits with Multiple Sclerosis.  I am working full time, and cannot afford to be overly sleepy.  I am very impressed with how it works.  It stimulates me mentally, without creating the "hyper" physicality of a general stimulant like caffiene.  I am able to take the medication on a when required basis - not more than 200 mg in a day - and it works great.  Many days I do not take it at all.  It has a long half-life, however."