Why is it that aqueous extracts of the Tea Plant is the most consumed beverage in the world? It's not the taste - it's because it's psychoactive.
The compound responsible is theanine - found only in the Tea Plant and a certain fungus (Bay Boleet). Theanine modulates the psychostimulant effect of caffeine, further increasing focus but also with a calming that has been shown to increase alpha waves in the brain - similar to meditative states (Nobre at al.).
Therefore there may be cognitive and anxiolytic properties of theanine in the presence of caffeine and possible as an isolated extract.
A. C. Nobre, A. Rao, and G. N. Owen. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr, 17(suppl - 1):167-168, 2008.