I got through studying for the bar purely on adderall. Study for twenty hours. Crash for ten. For about two weeks. As far as Amazon goes this stuff is definitely effective http://www.amazon.com/Caffeine-Nootropic-L-theanine-Focused-Recommended/dp/B00GXPNEUO

It would be cheaper if you get bulk powder but who wants to mess with that when studying for the bar.