What do you use to stay concentrated?

For me it always been an issue, how to perform better.
Tried a lot of stuff: mate, green tea, pu-erh tea, espresso.
Last things that I currently use from time to time: Sagan-Daila (Rhododendron adams), Ku Ding and nootropics.
I also wonder, if someone else used smart drugs/nootropics and has a knowledge about it.

In fact, I'm interested what are the tools you use to stay focused (especially when you don't have enough sleep) with a minimal amount of negative consequences.

* This article was originally published here