L-Theanine

USE: L-theanine is nature's “chill pill.”  L-theanine is an amino acid that helps calm the nervous system. It's also thought to be the secret to tea's subtle calming effects despite the caffeination. While it can help improve your quality of sleep, L-theanine is also helpful for reducing anxiety levels. These days, with so many people stressed to the max, it's an effective, drug-free alternative that enables you to take the edge off anytime the need arises.
SOURCE: Found primarily in Green tea.