I take 200 mg as a PRN, usually when I need to study which is about 4-5 days a week. At times I have taken as much as 600 mg in one day. It clears my mind, helps me concentrate and generally gives me mental stamina for about 4 hours. When on it I feel calm and it lifts my mood. Once it wears off though all the negative stuff, like agitation, depression or whatever else I am dealing with at the time, returns. Kinda wish I could take it all day but my pdoc only prescribes 200 mg 4-5 days a week.