What is L-theanine?

L-theanine is a naturally occurring amino acid, although it isn’t used as a building block for protein synthesis,^[1][2] unlike the 20 standard protein-forming amino acids that are synthesized by the genetic code. Several types of tea, including black, oolong, and green tea, contain theanine (generally <50 mg per serving).^[3][2][4] When higher doses are desired, theanine can also be taken as a dietary supplement; the theanine in supplements may be extracted from tea^[3] or chemically synthesized using bacterial enzymes.^[5]