L Theanine

L Theanine was discovered in green tea in 1949 and isolated from Yulu tea leaves in 1950 , accounting for approximately 1-2% of the dry weight of green tea .

Theanine typically refers to L-theanine (levo-form), which is the natural form found in tea leaves, while research on D-theanine (dextro-form) is less extensive . As a dietary supplement, the US Food and Drug Administration deems it safe to consume up to 250 mg per day . Common dosage forms include capsules, tablets, and powders, and it is often used in combination with caffeine.

L-theanine can cross the blood-brain barrier and may possess neuromodulatory functions through interacting with glutamate receptors. Animal experiments have demonstrated its potential sedative and immunomodulatory effects. However, the European Food Safety Authority has assessed that the current evidence is insufficient to support a causal relationship between L-theanine and improving cognitive function, relieving psychological stress, maintaining normal sleep, or alleviating menstrual discomfort .