Wiki can explain centro better than I can. It just makes your brain work better, one person told me it 'ungunks' it.
http://en.wikipedia.org/wiki/MeclofenoxateI took only vinpocetine(10mgx3/day) when I was in gas school, got 90 plus in both gas and electrical(class and exams) w/ little to no outside of the classroom studying.
Vinpocetine is cheap as fuck. like less than $10/month.
This is where I ordered from, so you can check the prices for yourself for whatever you're interested in.
http://www.smartpowders.com/All in all, my stack from previous post cost ~$220 or so with shipping(USA to Canada).
IMO, it's like brain nutrition, and I'm planning on medical school, so I look at it like an investment in myself.