Theanine (also gamma-glutamylethylamide or 5-N-ethyl-glutamine, is an amino acid and a glutamic acid analog commonly found in tea (infusions of Camellia sinensis), primarily in green tea, and also in the basidiomycete mushroom Boletus badius and in guayusa. More specifically, this compound is called L-theanine, being the L- amino acid (note: this is not the same as the levorotatory enantiomer). In 1950, the tea laboratory of Kyoto successfully separated theanine from gyokuro leaf, which has high theanine content. Theanine is an analog to glutamine and glutamate, and can cross the blood–brain barrier. It is sold in the US as a dietary supplement, and is FDA confirmed as generally recognized as safe (GRAS). The Japanese Ministry of Health and Welfare approved the use of theanine for universal consumption in 1964.

More information on the Wikipedia page [1].

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