L-theanine is an amino acid found naturally in tea leaves. It's one of four things in every piece of Neuchu, alongside caffeine, B vitamins and xylitol.
We pair it with caffeine at roughly a 1:1 ratio — 50mg of each per piece. That ratio shows up in a lot of gum and drink products that combine the two.
I'll leave the specifics of what it does in your body to your own research rather than making claims here — I'm not a doctor, and I'd rather point you toward accurate general information than oversell it.
What I can tell you is it's a normal part of a lot of people's daily caffeine routine already — green tea, certain coffee blends, and gum like ours.