Theanine (l-theanine) is an amino acid found in ordinary tea leaves from Camellia sinensis (also known as Thea sinensis, hence the name theanine). It is also found in other species of Camellia and in the edible bay boletes mushroom Xerocomus badius, but is otherwise rare in nature. L-theanine has the reputation for promoting mental and physical relaxation-decreasing stress and anxiety-without inducing drowsiness.