L-Theanine 150mg

60 capsules (vegetarian)
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L-Theanine 150mg

Regular Price: €17.50

Special Price €15.00

60 capsules (vegetarian)

* based on 6% VAT

RSG's L-Theanine is a pure supplement, developed specifically without chemical or pharmaceutical excipients. 
L-Theanine exclusively contains 150mg pure L-Theanine and natural acacia fibre. 
L-Theanine contains the left-handed enantiomer variant of theanine.

With THEA-opt ® quality mark 

Product Description


L-Theanine is a biological molecule, which is found mainly in tea leaves (Juneja, 1999) in more than 20 tea species and variants (Deng, 2010). Among other qualities, it has a biological and balancing effect on the brain and increases concentration. Tea leaves contain the levorotatory form of the amino acid Theanine, which is why Theanine is also called L-Theanine. This levorotatory variant is responsible for the effectiveness and the taste of mainly green tea. 

Tea contains approximately 2% pure amino acids and 50% of this is L-Theanine. In the tea plant it appears that–in addition to a role as a building material–it is also effective in protecting the cells. When young tea plants are stressed with salt, they produce additional L-Theanine in their cells (Deng, 2012). In a model for lifespan, the famous model of the nematode (roundworm), it emerged that Theanine considerably lengthens the lifespan of cells in roundworms (Zarse, 2012).

L-Theanine has been studied extensively and has been described in more than 200 scientific articles.

L-Theanine enters the blood stream quickly through tea or capsules; the more you take, the higher the concentration in your blood. However, to measurably increase the content of Theanine in blood, you would have to drink a great deal of tea, glass after glass (Scheid, 2012).

Second to water, tea is the liquid most drunk around the world (Graham, 1992). The special taste of green tea is caused to a large extent by the presence of the amino acid Theanine. In Japan this taste is called Umami (Narakuwa, 2008). Umami is considered the 5th taste sensation in Japan, after bitter, sour, salty and sweet. 

Physiological effect of Theanine 

Theanine has a physiological function in our brain.


Illustration (Wikipedia): the Theanine molecule

Theanine: a brief history of an important molecule

The amino acid L-Theanine was described for the first time in 1949 by a Japanese researcher, Dr. Sakato, as the most important ingredient in the tea plant (Camellia sinensis).

The unique effect that L-Theanine has on our brain has been known for more than 50 years (Kimura, 1971). Japanese physicians and biologists in particular carried out extensive research studies on the biological and balancing effects (Kimura, 1975; Shinozaki, 1978). These extraordinary effects were observed in a large number of lab animals, starting with the roundworm, later octopus and rats, and finally human beings were tested (Shinozaki, 1978; Kimura, 1980).

It quickly became clear that this amino acid can influence various neurotransmitter systems in the brain, such as dopamine, serotonin, glutamine and noradrenaline (Kimura, 1986; Yokogoshi, 1998; Yokogoshi, 2000; Yamada, 2005; Yamada 2007; Yamada, 2009).

Around 1990 Japanese researchers found that Theanine could also be produced in cell cultures of the tea plant (Orihara, 1990). Starting from the1990s, the biological effects of this amino acid were tested on various cell types and tissues in the body (Yokozawa, 1995; Kitaoka, 1996).

After drinking, Theanine is easily absorbed in the intestines and within a few hours definite concentrations of amino acid can be observed in the blood (Unno, 1999). During several hours after taking Theanine, the concentration in the brain increases and the maximum is reached after approximately five hours (Terashima, 1999).

Very fascinating is that it appears that the amino acid can normalise the excessively active effect of caffeine (Kakuda, 2000).

Theanine is a unique substance that also has a physiological function in assisting the immune system (Kurihara, 2007; Bukowski, 2008; Kawada, 2010; Kurihara, 2013).

The effects of the tea on brain function in humans can be seen via an EEG (Dimpfel, 2007; Gomez-Ramirez, 2007; Kelly, 2008; Ota, 2013).

The supporting effect of Theanine on brain cells was also observed by neurobiologists (Nishada, 2008; Takeda, 2011; 2012).

The same supportive effect applies as well to blood vessels (Siamwala, 2013).

Recently, cell biologists have also discovered that Theanine can support the physiological function of the DNA (Attia, 2012).

L-Theanine of RSG

RSG has specifically developed L-Theanine as a pure supplement, without chemical and pharmaceutical additives; only the pure amino acid L-Theanine was selected for this supplement. The vegetarian capsules contain nothing more than pure L-Theanine and natural acacia fibre.


JP Russell Science Global Ltd has opted for the term ‘Science’ in its name for good reasons. The company develops only natural products that are found in the cells and tissues of the body. These support important physiological functions. Furthermore, extensive scientific research has been carried out into its effects. Therefore, an extensive overview of scientific publications about the functions of Theanine can be found in the ‘Product Effects’ section of the website. These publications clearly demonstrate the biological relevance. 

The result of studying these natural substances is that RSG has chosen to produce products that are completely free of chemical and pharmaceutical additives – wherever possible. For example, the RSG’s Theanine capsules do NOT contain chemical additives and fillers such as magnesium stearate – a substance that unfortunately is found in many supplements. The capsules contain fillers made solely from natural acacia fibre, which is also known for it positive effect on the body.

Tested on purity

To guarantee the quality of this product, Theanine is tested for purity. The tests are carried out by an entirely independent and specialised scientific laboratory.

Inspect the test report here. (PDF)

The focus of RSG 

Especially for the consumer, RSG has formulated a series of supplements in such a manner that–in contrast to most supplements–they are completely free of unnecessary and superfluous pharmaceutical & chemical additives and fillers, such as magnesium stearate and preservatives.

Therefore, the Theanine formula of RSG consists only of three pure ingredients: Theanine, natural acacia fibre as filler and a vegetable capsule based on cellulose that contains the supplement.

Characteristics of RSG’s L-Theanine

  • 150 mg L-Theanine per capsule

  • Vegetarian capsules

  • Contains natural acacia fibre for filling up the capsule

  • Completely free of chemical & pharmaceutical additives and fillers

  • Completely free of gluten, dairy, soya and genetically modified organisms (GMO)

  • Contains natural and biologically active amino acid L-Theanine

  • Contains only the levorotatory variant of Theanine

  • High quality

  • High purity

Terms for L-Theanine

5-N-ethylglutamine, 2-Amino-4-(ethylcarbamoyl)butyric acid.


Ingredients per capsule:

  • 150 mg L-Theanine; * (the natural levorotatory variant)

  • Natural acacia fibre

  • Vegetarian capsule (hydroxypropyl methylcellulose)

* The recommended daily dosage has not been determined.


L-Theanine originates from the tea plant and therefore does not contain any known allergens, such as soya, corn, wheat, gluten, yeast, lupine, peanuts, celery, mustard, nuts, sesame, shellfish, crustacean, mollusc, cow milk, eggs and fish.

In addition, the supplement is free of genetically modified organisms (GMO), added sucrose, gelatine, preservatives and artificial colourings, fragrances and flavourings.

Vegetarians & Vegans: 

L-Theanine is extracted from the tea plant and is therefore suitable for vegetarians and vegans.


L-Theanine was very extensively examined on safety and is considered to be Generally Recognized As Safe (GRAS). Long-term use during a few years has never led to any severe negative effects. For the time being, there are no indications that continuous use of L-Theanine will cause any problems. Dosage of 200 mg two to three times per day up to 400 mg three times per day can be ingested without any worries. In special animal models measured for safety, it emerged that higher dosage over a long period of time had no side effects (Borzelleca, 2006).

Strengthening effect of L-Theanine on other supplements

There are several supplements that reinforce each other in a positive manner, such as the combination of L-Theanine and palmitoylethanolamide (PeaPure). In addition, vitamin B-complex and vitamin D3 as well as L-Acetyl-Carnitine (Alcar) constitute strong combinations with L-Theanine.

Instructions for Use

Recommended dosage: 

It is advised to take 1 vegetarian capsule 2-3 per day, preferably on an empty stomach, unless advised otherwise.
Recommended daily dosage (3 capsules) is 450mg L-Theanine.
The effect on mental balance is usually noticed quickly, usually within 30 minutes to 1 hour after ingestion.

Product Effect

As producer of food supplement, we are only permitted–pursuant to recent regulations–to give limited information about the effects of food supplements. For further information, we refer you to other sources / Internet sources.


Literature about L-Theanine

Attia S. Modulation of irinotecan-induced genomic DNA damage by Theanine. Food Chem Toxicol. 2012 May;50(5):1749-54.

 Borzelleca JF, Peters D, Hall W. A 13-week dietary toxicity and toxicokinetic study with l-Theanine in rats. Food Chem Toxicol. 2006 Jul;44(7):1158-66.

Bukowski JF, Percival SS. L-Theanine intervention enhances human gammadeltaT lymphocyte function. Nutr Rev. 2008 Feb;66(2):96-102.

Deng WW, Ogita S, Ashihara H. Distribution and biosynthesis of Theanine in Theaceae plants. Plant Physiol Biochem. 2010 Jan;48(1):70-2.

Deng WW, Wang S, Chen Q, Zhang ZZ, Hu XY. Effect of salt treatment on Theanine biosynthesis in Camellia sinensis seedlings. Plant Physiol Biochem. 2012 Jul;56:35-40.

Dimpfel W, Kler A, Kriesl E, Lehnfeld R, Keplinger-Dimpfel IK.

Source density analysis of the human EEG after ingestion of a drink containing decaffeinated extract of green tea enriched with L-Theanine and theogallin. Nutr Neurosci. 2007 Jun-Aug;10(3-4):169-80. 

Gomez-Ramirez M, Higgins BA, Rycroft JA, Owen GN, Mahoney J, Shpaner M, Foxe JJ. The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of Theanine. Clin Neuropharmacol. 2007 Jan-Feb;30(1):25-38.

Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med. 1992 May;21(3):334-50.

Juneja LR, Chu D, Okubo T, et al. L-Theanine – a unique amino acid of green tea and its relaxation effect in humans. Food Sci Tech 1999;10:199-204.

Kakuda T, Nozawa A, Unno T, Okamura N, Okai O.

Inhibiting effects of Theanine on caffeine stimulation evaluated by EEG in the rat. Biosci Biotechnol Biochem. 2000 Feb;64(2):287-93.

Kawada S, Kobayashi K, Ohtani M, Fukusaki C. Cystine and Theanine supplementation restores high-intensity resistance exercise-induced attenuation of natural killer cell activity in well-trained men. J Strength Cond Res. 2010 Mar;24(3):846-51.

Kelly SP, Gomez-Ramirez M, Montesi JL, Foxe JJ. L-Theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance. J Nutr. 2008 Aug;138(8):1572S-1577S.

Kimura R, Murata T. Influence of alkylamides of glutamic acid and related compounds on the central nervous system. I. Central depressant effect of Theanine. Chem Pharm Bull (Tokyo). 1971 Jun;19(6):1257-61. 

Kimura R, Kurita M, Murata T. Influence of alkylamides of glutamic acid and related compounds on the central nervous system. III. Effect of Theanine on spontaneous activity of mice]. Yakugaku Zasshi. 1975 Jul;95(7):892-5.

Kimura R, Murata T. Influence of alkylamides of glutamic acid and related compounds on the central nervous system. IV. Effect of Theanine on adenosine 3',5'-monophosphate formation in rat cerebral cortex. Chem Pharm Bull (Tokyo). 1980 Feb;28(2):664-6.

Kimura R, Murata T. Effect of Theanine on norepinephrine and serotonin levels in rat brain. Chem Pharm Bull (Tokyo). 1986 Jul;34(7):3053-7.

Kitaoka S, Hayashi H, Yokogoshi H, Suzuki Y. Transmural potential changes associated with the in vitro absorption of Theanine in the guinea pig intestine. Biosci Biotechnol Biochem. 1996 Nov;60(11):1768-71. 

Kurihara S, Shibahara S, Arisaka H, Akiyama Y. Enhancement of antigen-specific immunoglobulin G production in mice by co-administration of L-cystine and L-Theanine. J Vet Med Sci. 2007 Dec;69(12):1263-70.

Kurihara S, Shibakusa T, Tanaka KA. Cystine and Theanine: amino acids as oral immunomodulative nutrients. Springerplus. 2013 Nov 26;2:635. eCollection 2013.

Narukawa M, Morita K, Hayashi Y. L-Theanine elicits an umami taste with inosine 5'-monophosphate. Biosci Biotechnol Biochem. 2008 Nov;72(11):3015-7. 

Nishida K, Yasuda E, Nagasawa K, Fujimoto S. Altered levels of oxidation and phospholipase C isozyme expression in the brains of Theanine-administered rats. Biol Pharm Bull. 2008 May;31(5):857-60.

Orihara Y, Furuya T. Production of Theanine and other γ-glutamyl derivatives by Camellia sinensis cultured cells. Plant Cell Rep. 1990 Jul;9(2):65-8. doi: 10.1007/BF00231550.

Ota M, Wakabayashi C, Matsuo J, Kinoshita Y, Hori H, Hattori K, Sasayama D, Teraishi T, Obu S, Ozawa H, Kunugi H. Effect of L-Theanine on sensorimotor gating in healthy human subjects. Psychiatry Clin Neurosci. 2013 Dec 25. doi: 10.1111/pcn.12134

Sakato Y. The chemical constituents of tea: III. A new amide Theanine. Nippon Nogeikagaku Kaishi 1949;23:262-267.

Scheid L, Ellinger S, Alteheld B, Herholz H, Ellinger J, Henn T, Helfrich HP, Stehle P. 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 Dec;142(12):2091-6.

Shinozaki H, Ishida M. Theanine as a glutamate antagonist at a crayfish neuromuscular junction. Brain Res. 1978 Jul 28;151(1):215-9.

Siamwala JH, Dias PM, Majumder S, Joshi MK, Sinkar VP, Banerjee G, Chatterjee S. L-Theanine promotes nitric oxide production in endothelial cells through eNOS phosphorylation. J Nutr Biochem. 2013 Mar;24(3):595-605.

Shulman M. A soothing sip of focus. The latest on tea: it might quiet distracted minds. US News World Rep. 2007 Oct 8;143(12):58.

Takeda A, Sakamoto K, Tamano H, Fukura K, Inui N, Suh SW, Won SJ, Yokogoshi H. Facilitated neurogenesis in the developing hippocampus after intake of Theanine, an amino acid in tea leaves, and object recognition memory. Cell Mol Neurobiol. 2011 Oct;31(7):1079-88. 

Takeda A, Tamano H, Suzuki M, Sakamoto K, Oku N, Yokogoshi H.

Unique induction of CA1 LTP components after intake of Theanine, an amino acid in tea leaves and its effect on stress response. Cell Mol Neurobiol. 2012 Jan;32(1):41-8.

Terashima T, Takido J, Yokogoshi H. Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with Theanine. Biosci Biotechnol Biochem. 1999 Apr;63(4):615-8.

Unno T, Suzuki Y, Kakuda T, Hayakawa T, Tsuge H. Metabolism of Theanine, gamma-glutamylethylamide, in rats. J Agric Food Chem. 1999 Apr;47(4):1593-6.

Yamada T, Terashima T, Okubo T, Juneja LR, Yokogoshi H. Effects of Theanine, r-glutamylethylamide, on neurotransmitter release and its relationship with glutamic acid neurotransmission. Nutr Neurosci. 2005 Aug;8(4):219-26.

Yamada T, Terashima T, Wada K, Ueda S, Ito M, Okubo T, Juneja LR, Yokogoshi H. Theanine, r-glutamylethylamide, increases neurotransmission concentrations and neurotrophin mRNA levels in the brain during lactation. Life Sci. 2007 Sep 29;81(16):1247-55. Epub 2007 Aug 31.

Yamada T, Terashima T, Kawano S, Furuno R, Okubo T, Juneja LR, Yokogoshi H.

Theanine, gamma-glutamylethylamide, a unique amino acid in tea leaves, modulates neurotransmitter concentrations in the brain striatum interstitium in conscious rats. Amino Acids. 2009 Jan;36(1):21-7.

Yokozawa T, Oura H, Nakagawa H, Sakanaka S, Kim M. Effects of a component of green tea on the proliferation of vascular smooth muscle cells. Biosci Biotechnol Biochem. 1995 Nov;59(11):2134-6.

Yokogoshi H, Kobayashi M, Mochizuki M, Terashima T. Effect of Theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats. Neurochem Res. 1998 May;23(5):667-73.

Yokogoshi H, Terashima T. Effect of Theanine, r-glutamylethylamide, on brain monoamines, striatal dopamine release and some kinds of behavior in rats. Nutrition. 2000 Sep;16(9):776-7.

Zarse K, Jabin S, Ristow M. L-Theanine extends lifespan of adult Caenorhabditis elegans. Eur J Nutr. 2012 Sep;51(6):765-8.