L-theanine 101: The sneaky popular nootropic in your drink

L-theanine has become your beverage’s favorite amino acid. Showing up in sparkling waters, mocktails, and other ready-to-drink concoctions, L-theanine has a host of purported benefits for your brain—but what is L-theanine, exactly? Science points to its unique ability to promote a state of relaxed alertness, thanks to its role in increasing alpha-brain waves.