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Ingredient Type: Amino acid 

Also Known As: Gamma-ethylamino-L-glutamic acid, γ-L-Glutamylethylamide

L-Theanine is a non-essential amino acid found primarily in tea leaves (specifically Green Tea), but it has also been isolated in mushrooms.  It was discovered in green tea in Japan in 1949 and has since become a popular additive to foods.  It is believed to calm stress, boost mood, and improve cognitive performance.

L-Theanine has a chemical structure very similar to glutamate, an amino acid that occurs naturally in the body and helps transmit nerve impulses in the brain.


L-Theanine is used in health supplements today to promote relaxation and focused concentration.


Cognitive Performance: Preliminary clinical research shows that taking theanine 100 mg prior to cognitive testing reduces the rate of errors compared with placebo in healthy adults.

Stress: One clinical study shows that taking L-theanine (Taiyo Kagaku) 200 mg prior to a psychological exam reduced tension-anxiety and prevented blood pressure increases caused by psychological stress.  Other preliminary clinical research shows that pharmacy students taking theanine 200 mg twice daily for one week prior to and for the first 10 days of a pharmacy practice period had decreased subjective stress scores compared to placebo.


Theanine is possibly safe when used orally, short-term.  Theanine has been used safely once per week for 3 weeks.  It is not known if use for longer periods of time is safe.  Theanine is sold in the United States as a dietary supplement and has been granted GRAS (generally recognized as safe) status for food by the Food and Drug Administration.  Few adverse reactions have been reported.  Adverse reactions recorded in human studies using tea extracts include a headache, dizziness, and mild GI symptoms.


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  3. Scheid L, et al. Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanine via capsules and green tea. J Nutr. 2012;142(12):2091-2096.
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  9. Lu K, Gray MA, Oliver C, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol 2004;19:457-65
  10. Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., and Scholey, A. B. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol.Psychol. 2008;77(2):113-122
  11. Matsumoto, K., Yamada, H., Takuma, N., Niino, H., and Sagesaka, Y. M. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC.Complement Altern.Med. 2011;11:15
  12. Giesbrecht, T., Rycroft, J. A., Rowson, M. J., and De Bruin, E. A. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-290.
  13. Camfield DA, Stough C, Farrimond J, Scholey AB. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutr Rev. 2014;72(8):507-522

See the entry for theanine, the entry for theanine, the RXList entry for theanine, or the WebMD entry for theanine for more information.