We care about safety first and effectiveness second. Here are some informational reads about the L-theanine + caffeine combo.

https://nootrobox.com/theanine

http://www.maneyonline.com/doi/abs/10.1179/147683010X1261146...

https://nootrobox.com/assets/2008-owen-b0b4e2568156b1c5a8574...