L-theanine is a water-soluble amino acid. Amino acids are the building blocks of proteins. L-theanine has been studied for its possible health benefits, ranging from cancer and stroke prevention to weight loss. However, most research on the amino acid has been conducted to assess its stress-relieving effects.1


L-theanine is found mainly in tea (eg, green tea and black tea), and to a less extent in mushrooms. L-theanine is also available in its purified form as an oral dietary supplement.1

Therapeutic Dosages    TOP

Optimal doses of tea or its constituents are not known.

Therapeutic Uses    TOP

L-theanine is thought to have both antioxidant and relaxant effects.1 Some animal studies have shown that the amino acid may also be helpful in lowering lipids in the blood, fighting obesity, and preventing cognitive dysfunction and stroke.1 L-theanine has been shown to increase the anti-tumor activity of two cancer-fighting drugs, doxorubicin and idarubicin.2,3

What Is the Scientific Evidence for L-Theanine?    TOP

Although there have been a handful of studies evaluating L-theanine for several conditions,13 most research has been centered on its effects on mental status.

L-theanine has been shown to have a direct influence on brain activity, such as reducing stress.4,12 At high doses (higher than usual doses found in a cup of black tea [20 mg (milligrams)]), it has the ability to relax the mind without causing drowsiness. One study measured a type of activity in the brain, called alpha activity, which plays an important role in attention.5 Thirty-five participants were given either 50 mg of L-theanine or placebo. Electroencephalogram (EEG) tests were done at baseline and then at specified times afterwards (45, 60, 75, 90, and 105 minutes). Researchers found that there was a greater increase in alpha activity in those who took L-theanine compared to placebo, demonstrating that the amino acid had an effect on the participants’ general state of mental alertness and arousal.

A handful of studies have also looked at the combination of L-theanine and caffeine on various aspects of cognition and mood (eg, alertness, attention).8,9,10,11 For instance, one study compared the effect of caffeine with and without L-theanine on cognition and mood in 27 participants.10 Researchers gave participants placebo, caffeine, or caffeine plus L-theanine and measured their performance on several cognitive tests at baseline and then at 60 and 90 minutes after treatment. They found that the combination of caffeine and L-theanine improved speed and accuracy in an attention-switching task, as well as reduced the likelihood of distraction during a memory task. Caffeine alone did improve alertness and accuracy.

Researchers in Korea conducted a randomized, double-blind, placebo-controlled study to look at the effect of L-theanine on memory and attention in 91 people with mild cognitive impairment.6 Half of the participants were given 1,680 mg of L-theanine (LGNC-07) and the other half was given placebo for 16 weeks. Memory and word tests were conducted, as well as EEG tests. The researchers found that L-theanine improved memory and selective attention, as well as cognitive alertness.

Another small study also found the amino acid to have a positive effect in reducing anxiety.7 The double-blind, randomized, placebo-controlled study was made up of 60 people diagnosed with schizophrenia or schizoaffective disorder. Of the 40 patients who completed the study, L-theanine was associated with reduced anxiety and was found to be well-tolerated and safe.

Safety Issues    TOP

There have not been any side effects reported from taking L-theanine. However, drinking large amounts of green tea in general may cause upset stomach, irritability, and nausea due to the tea’s caffeine content. Also, do not take L-theanine if undergoing chemotherapy or are taking lipid-lowering medicines or sedatives, since L-theanine may alter the effects of these drugs.

References:[ + ]

1. L-theanine. Memorial Sloan-Kettering Cancer Center website. Available at: http://www.mskcc.org/mskcc/html/69285.cfm. Updated December 10, 2010. Accessed August 15, 2011.

2. Sugiyama T, Sadzuka Y. Combination of L-theanine with doxorubicin inhibits hepatic metastasis of M5076 ovarian sarcoma. Clin Cancer Res. 1999;5(2):413-416.

3. Sadzuka Y, Sugiyama T, Sonobe T. Improvement of idarubicin induced antitumor activity and bone marrow suppression by L-theanine, a component of tea. Cancer Lett. 2000;158(2):119-124.

4. Juneja LR. Suntheanine and its relaxation effect in humans. Trends in Food Science & Tech. 1999;10;199-204.

5. Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-168.

6. Park SK, Jung IC, Lee WK, et al. A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study. J Med Food. 2011;14(4):334-343.

7. Ritsner MS, Miodownik C, Ratner Y, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study. J Clin Psychiatry. 2011;72(1):34-42.

8. Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-290.

9. Einöther SJ, Martens VE, Rycroft JA, De Bruin EA. L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness. Appetite. 2010;54(2):406-409.

10. Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008;11(4):193-198.

11. Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine, and their combination on cognition and mood. Biol Psychol. 2008;77(2):113-122.

12. Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007;74(1):39-45.

13. Miyagawa K, Hayashi Y, Kurihara S, Maeda A. Co-administration of l-cystine and l-theanine enhances efficacy of influenza vaccination in elderly persons: nutritional status-dependent immunogenicity. Geriatr Gerontol Int. 2008;8(4):243-250.

Last reviewed August 2013 by EBSCO CAM Review Board
Last Updated: 8/22/2013