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L-theanine is an amino acid that is essentially found in leaves of green tea, white tea, and black tea or even mushrooms. Theanine is obtained from tea (Camellia sinensis) leaves, and tea is an evergreen tree/shrub that is native to eastern Asia and belongs to the family of Theaceae. The edible mushrooms (Xerocomus badius) that mainly grow in the United States during late summer and autumn also contain this chemical. L-theanine is not an essential dietary amino acid, and it is also a non-protein amino acid. Technically, it is referred to as r-glutamyl ethyl amide and is popularly thought to be a sedative (relaxing) amino acid. L-theanine is a water soluble amino acid that crosses the blood-brain barrier in about 30 minutes after consumption. It is also referred to as 5-N-Ethyl-Glutamine, Suntheanine, and Gamma-ethylamino-L-glutamic acid (scientific name).

L-theanine has a structure that is closely similar to that of the neurotransmitters glutamate and GABA. Glutamate is an amino acid that naturally occurs within the human body, and it assists in the transmission of nerve impulses in the brain. It is synthesized by altering one of the carboxylic ends in glutamic acid with an additional amino group and then an ethyl group. Since the addition of the amino group to the glutamic acid produces Glutamine, the structure of theanine is an ethylated derivative of glutamine. Theanine has various brands but Suntheanine® is the most popular brand of theanine that is said to contain over 99% L-theanine isomer. Suntheanine is manufactured from a mixture of Glutamine with an ethylamine derivative, and it is patented by Taiyo Kagaku Co. Suntheanine has been employed in various scientific and clinical studies that are seeking the standardization of L-theanine. Theanine is mostly used to treat high blood pressure and anxiety, to make cancer drugs more efficient and to prevent Alzheimer's disease. It is also used for stress relief, to improve focus and concentration, and to minimize cognitive impairment.


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L-theanine was first synthesized from leaves of green tea tree (Camellia sinensi) in 1949 by Sakato in Japan. In 1950, it was first isolated from tea leaf by a laboratory in Kyoto. Japan in 1964 approved the unlimited use of L-theanine in all food products including soft drinks, herb teas, and chocolates with an exception for infant food products. Theanine occurs in nature mostly as an L-(s) enantiomer but synthetic Theanine is produced as a racemic mixture of L-enantiomer and D-enantiomer forms. Suntheanine, the patented pure form of L-theanine was developed by Taiyo (a pioneer in green tea science). Taiyo had observed that green tea had relaxation effect due to its amino acid L-theanine compounds. However, Suntheanine is not extracted from tea. It is synthesized through a patented fermentation process similar to the natural process in green tea leaves, and the end product is the 100% pure L-isomer-theanine.

The demand for L-theanine has experienced an upsurge of late because the substance is linked to various health benefits like enhancement of concentration, relaxation, learning ability, and enhanced the functioning of the immune system, prevention of some cancers and cardiovascular conditions, and promotion of weight loss. Even with the chemical and biological synthesis of theanine being successful, scientific research still focuses on efficient techniques of isolating theanine from its natural sources.


In a 2011 clinical trial, researchers examined the effects of L-theanine on attention and reaction time. The double-blind study involved 18 healthy university students. Manifest Anxiety Scale (MAS) was used to measure the anxiety levels and then the individuals were allocated to two groups of minimal anxiety and high anxiety. L-theanine and a placebo were administered at doses of 200mg and in about 15-60 minutes after the administrations, the subjects took the visual attention task and audio response test. Other measures were EGG alpha wave activity, State-Trial Anxiety Inventory, and heart rate. The researchers observed increases in alpha waves, enhanced performance, and decreased heart rate in individuals who had high-anxiety after administration with the 200mg L-theanine dose. As such, L-theanine supplementation in persons with anxiety has positive effects as it seems to normalize neurotransmission and neuroelectrical activity.

Another trial examined the effects of L-theanine on cognition in individuals with stress. The 14 subjects were administered with L-theanine +Placebo, Placebo, or Caffeine+Placebo and researchers recorded the observations. Blood pressure was among the secondary measures used. According to the results, the high-stress subjects who were administered with L-theanine exhibited significantly lower blood pressure than the others when faced with a stressor. The researchers associated the drop in blood pressure with L-theanine supplementation to its anxiolytic properties.

A 2008 study investigated the effects of theanine and caffeine in a placebo-controlled, randomized, double-blind trial. The 48 subjects (adults) were administered with 200mg theanine, 250mg caffeine, a mixture of caffeine and theanine, or neither. The blood pressure of the subjects was recorded before supplementation and 40 minutes post supplementation. The researchers observed that theanine offsets the caffeine induced hypertension when the two were administered as a mixture. As such, theanine could be a potential remedy for persons who have caffeine induced hypertension. However, this study was small and further research is necessary.

A meta-analysis was undertaken to analyze the effects of L-theanine on mood and cognitive function when administered solo or in combination with caffeine. Results from eleven studies that were randomized and placebo controlled were used in the analysis. In all the 11 studies, assessments used the Bond-Lader scale (used to measure calmness, alertness, and contentedness), State-Trait Anxiety Inventory (to measure anxiety), and other different cognitive measures to monitor intersensory attention, visual information processing, and attention switching. The combination of caffeine and L-theanine was seen to cause the highest cognitive enhancement. This conclusion was based mainly on the significant enhancements noted in measures of attention switching and alertness indicating increases in cognitive flexibility. Based on this meta-analysis, evidence shows that a combined administration of L-theanine and caffeine causes substantial cognitive improvements.

A clinical trial conducted to examine the effects of L-theanine on human leukemia and lung cancer cells showed positive effects. L-theanine was observed to suppress the growth of leukemia and lung cancer cell lines. The suppression was seen to be affected by factors related to the dosing and time of administering L-theanine. It was also noted that L-theanine boosted the anti-cancer effects of different anticancer agents. Based on the results of the study, L-theanine may have significant healing potential in the management of leukemia and cancer. Many anticancer agents have adverse reactions and side effects, and L-theanine has been observed to boost the efficacy of different anticancer agents. Researchers conducted a study to investigate if L-theanine could also help reduce the adverse physiological effects of anticancer drugs. L-theanine was administered to mice that had affected levels of glutamate and glutathione after treatments with doxorubicin. L-theanine was observed to lower a variety of adverse reactions caused by doxorubicin. It was also noted to boost glutamate concentrations within tumors. Additionally, L-theanine was observed to attenuate glutathione reductions that had been caused by doxorubicin intake while lessening the oxidative damage.

Animal-based research has shown that L-theanine has the potential to boost cognitive function and also offers neuroprotective benefit. Animal research showed that L-theanine modifies the levels of GABA, serotonin, and dopamine and it also has a corresponding effect on kainite, AMPA, and NMDA receptors. It also seems to alter behavior to help improve memory function and learning the ability. This nootropic effect is linked to the complex mechanism of L-theanine. Clinical trials on the cognitive effects of L-theanine administration in humans are limited, but the general perception is that L-theanine supplementation may be helpful to certain features of cognition.

Studies have also been conducted to assess the effects of L-theanine on obesity and weight loss. In one animal-based study, the anti-obese properties of L-theanine, caffeine, and catechins were evaluated. The impact of the three compounds was tested in mice that were provided with diets that had 2% green tea powder (with different quantities of the three compounds) for 16 weeks. The observations noted that L-theanine and caffeine led to reductions in body fat and body weight. There is substantial evidence suggesting that L-theanine, caffeine and catechins work in synergy to avoid obesity.

A recent clinical study investigated the effects of L-theanine in individuals suffering from schizophrenia. The researchers recruited 17 subjects who were administered with a combination of L-theanine and an antipsychotic medication for 8 weeks. The sleep quality of all participants was monitored using the Pittsburgh Sleep Index. The study results showed significant enhancements in sleep quality during the 8 weeks of the study after L-theanine supplementation. Researchers attributed the improved sleep quality to glutamatergic modulation. Sleep quality is also thought to improve in individuals with normal mental health and not just in schizophrenia patients.

A report published in 2008 shows that L-theanine boosts the activation of gamma delta T cells. Within the body, gamma delta T cells inhibit the growth of tumors and also act as protective agents. This backs the observation that in patients with tumors, L-theanine intake may have significant benefits. As such, L-theanine can lower the growth of tumors and the spread of malignant cells.

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