L-theanine is an amino acid found in green tea. As a supplement it is mostly used for stress, relaxation and sleep, and it is also added to some drinks.
Also known as: theanine.
L-theanine has no intake value or upper limit. A 2020 systematic review (Williams) of trials on stress and anxiety found the studies pointed to 200 to 400 mg a day; a 4-week trial used 200 mg a day (Hidese 2019). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. There is no FDA-approved L-theanine drug.
The 2020 review (Williams) concluded that 200 to 400 mg a day may help reduce stress and anxiety in people under stressful conditions, but that longer and larger studies are needed. In a 4-week crossover trial of 30 healthy adults (Hidese 2019), 200 mg a day improved scores for depression, anxiety and sleep quality compared with placebo. In the body, L-theanine appears to be broken down into ethylamine and glutamic acid (Scheid 2012).
In 12 healthy people given 100 mg (Scheid 2012), L-theanine peaked in blood about 0.8 hours after intake, whether taken as a capsule or in green tea, and exposure rose with dose from 50 to 200 mg. The study does not report a half-life we could confirm, so we do not list one.
Numbers shown are taken from the source above. Half-life varies from person to person.
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