A Cup of Tea Delivers L-Theanine to Your Emotional Rescue!

Krista Anderson-Ross ND | July 6, 2021

The neurologically active amino acid l–theanine is found primarily in plants used for tea. Along with water, tea is the most commonly consumed beverage in the world, existing in the forms of green, white, black, oolong and pu-erh.

Every type of tea comes from the same plant, Camellia Sinensis, but each is processed differently. White tea comes from the bud of the tea plant, and is not rolled or oxidized. To produce green tea, freshly harvested leaves are steamed to prevent fermentation. This steaming process destroys the enzymes that are responsible for breaking down color pigments so the leaves maintain their green color. The oolong, black and pu-erh types are the result of enzymatic oxidation and/or fermentation.1 The extent of fermentation has been found to determine the concentration of theanine, with more theanine contained in unfermented teas and less in fermented teas.2

Theanine levels vary in the different kinds of tea, with the least processed teas, green and white, generally having higher levels than the more processed black and olong, and pu-erh shown to contain no theanine. Analysis by Ekborg-Ott et al. revealed that the average theanine content of black teas was 1.4%, compared to 1.42% in green teas, and 1.16% in oolong.

The most important pharmacological effects of tea have to do with the central nervous system. While caffeine is a well-known stimulant, theanine has a relaxing effect. Boros et al. investigated the ratio between caffeine and theanine to explore the stimulatory vs excitatory impacts of tea. Generally speaking, the researchers found green and white tea to have the lowest caffeine/theanine ratio indicating the least stimulatory effect, versus black and oolong with a higher ratio indicating a more stimulatory effect.

Theanine is known to readily cross the blood brain barrier (BBB) where it has reported effects on the central nervous system including increased alpha wave brain activity. Animal studies have demonstrated theanine’s modulatory effects on neurotransmitters by increasing GABA levels, decreasing norepinephrine levels, and both increasing and decreasing dopamine, serotonin, glutamate and glycine levels in various areas of the brain.6, 7

Extracellular glutamate can cause neuronal cell death by acting as a powerful neurotoxin in the CNS. Another distinctive feature of theanine is its ability to bind to glutamate receptors serving as a competitive inhibitor, leading to attenuated glutamate-induced apoptosis.7, 6 

Several small human studies have confirmed theanine’s neuro-modulatory effects including an inhibitory effect in children with ADHD, attenuating the stress response, and demonstrating beneficial effects on the low mood, anxiety, sleep disturbance and cognitive impairments associated with depression.10, 11, 12

When administered orally, theanine peaks in the serum within an hour of administration reaching peak brain level within 5 hours, and gradually decreases to a non-detectable level over 19 hours.6 A common dosage in the medical literature is 200 mg. Theanine has been shown to be neuroprotective, anti-inflammatory, stimulatory to nerve growth factor BDNF, and inhibitory of cellular oxidation, showing promise for Alzheimer’s treatment.8, 9

So, pour yourself a cup of hot or iced tea and let your increased mental acuity guide you to ponder the wonders of theanine as a treatment mainstay. You may also pair this with the urinary measurement of neurotransmitters to marry both the art and science of natural medicine. Cheers!



1. Chacko SM, Thambi PT, Kuttan R, Nishigaki I. Beneficial effects of green tea: a literature review. Chin Med. 2010;5:13. Published 2010 Apr 6. doi:10.1186/1749-8546-5-13

2. Boros K, Jedlinszki N, Csupor D. Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples. Pharmacogn Mag. 2016;12(45):75-79. doi:10.4103/0973-1296.176061

3. https://lpi.oregonstate.edu/mic/food-beverages/tea#types

4. Ekborg-Ott KH, Taylor A, Armstrong DW. Varietal differences in the total and enantiomeric composition of theanine in tea. J Agric Food Chem. 1997;45:353–63.

5. Mason R. 200 mg of zen: l-theanine boosts alpha waves, promotes alert relaxation. Alternative and Complementary Therapies. 2001;7(2):91-95.

6. Lardner AL. Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disorders. Nutritional Neuroscience. 2014;17(4):145-155.

7. Nathan PJ, Lu K, Gray M, Oliver C. The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. J Herb Pharmacother. 2006;6(2):21-30. PMID: 17182482.

8. Cascella M, Bimonte S, Muzio MR, Schiavone V, Cuomo A. The efficacy of Epigallocatechin-3-gallate (green tea) in the treatment of Alzheimer's disease: an overview of pre-clinical studies and translational perspectives in clinical practice. Infect Agent Cancer. 2017;12:36. Published 2017 Jun 19. doi:10.1186/s13027-017-0145-6

9. Polito CA, Cai ZY, Shi YL, et al. Association of Tea Consumption with Risk of Alzheimer's Disease and Anti-Beta-Amyloid Effects of Tea. Nutrients. 2018;10(5):655. Published 2018 May 22. doi:10.3390/nu10050655

10. Hidese S, Ota M, Wakabayashi C, Noda T, Ozawa H, Okubo T, Kunugi H. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatr. 2017 Apr;29(2):72-79. doi: 10.1017/neu.2016.33. Epub 2016 Jul 11. PMID: 27396868.

11. Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. 2019 Oct 3;11(10):2362. doi: 10.3390/nu11102362. PMID: 31623400; PMCID: PMC6836118.

12. Kahathuduwa CN, Wakefield S, West BD, Blume J, Dassanayake TL, Weerasinghe VS, Mastergeorge A. Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT. Sci Rep. 2020 Aug 4;10(1):13072. doi: 10.1038/s41598-020-70037-7. PMID: 32753637; PMCID: PMC7403383.

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