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]
What is L-theanine?
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•Last Updated: May 16, 2025
L-Theanine is a naturally occurring amino acid that is found in various types of tea (such as black, oolong, and green tea) and is typically present in amounts less than 50 mg per serving. It can also be taken as a dietary supplement, which may be derived from tea or synthesized using bacterial enzymes.