L-Theanine For Mood & Mental Alertness

A cup of tea with a stylish half shot of a kettle.
Nothing like a fresh cup of tea - it contains a relaxant, L-Theanine. Photo by Stuart Miles, courtesy of FreeDigitalPhotos.net

L-theanine is a really fascinating compound found mostly in green tea, matcha and guayusa and the edible bay boletes mushroom, Xerocomus badius. It is thought to be the reason behind the calming and relaxing characteristic of beverages like tea (Juneja et al., 1999). After all, when you want something to relax you after a hard day, it’s quite often tea that is called for.  

L-Theanine is an amino-acid which is not found in proteins. It is also known as gamma-glutamylethylamide. L-theanine is the major one in tea where it forms 1 – 2% by dry weight  and this corresponds to 25-60mg per 200ml serving (Cartwright et al., 1954).

We know of some who drink tea after they have drunk too much coffee and this could well be due to the presence of theanine because it counters the effects of too much caffeine but doesn’t cause drowsiness or sleep.


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Taiyo International Inc., in Minneapolis, Minn. (www.taiyointernational.com) offer the ingredient as 100% pure L-isomer under the brand name Suntheanine® for use in formulations. This product is produced by their patented fermentation product which mimics the creation process in the green tea leaves themselves.

It is often consumed as a supplement, usually one or two 200mg capsules, to be taken with food. Take a couple when waking up and then wait a few hours before taking the next dose.  It is an effective alternative to St John’s Wort which is also used for its calming abilities and doesn’t interfere with birth control pills.  I suggest trying it as a supplement from suppliers like Solgar. If green tea is more your thing than a capsule, then try Pukka‘s green tea brand.

Clinical Evidence

The evidence for theanine’s benefits comes from clinical studies which indicate that between 50 mg and 200 mg helps naturally stimulate alpha wave activity in the brain. This is associated with mental alertness whilst maintaining a relaxed state.

In animal models, l-theanine shows activity in decreasing blood pressure and improving learning ability (Kim et al., 2009).

As well as the aforementioned improvement in mood state, a human study by Higashiyama and his team (2011) found that L-theanine significantly improved attentiveness and reaction responsiveness.  It is not addictive.

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Cartwright, R. A., Roberts, E. A. H., & Wood, D. J. (1954). Theanine, an amino‐acid n‐ethyl amide present in tea. Journal of the Science of Food and Agriculture, 5(12), pp. 597-599.
Juneja, L. R., Chu, D. C., Okubo, T., Nagato, Y., & Yokogoshi, H. (1999). L-theanine—a unique amino acid of green tea and its relaxation effect in humans. Trends in Food Science & Technology, 10(6), pp. 199-204
Higashiyama, A., Htay, H. H., Ozeki, M., Juneja, L. R., & Kapoor, M. P. (2011). Effects of l-theanine on attention and reaction time response. J. Functional Foods, 3(3), pp. 171-178
Kim, T. I., Lee, Y. K., Park, S. G., Choi, I. S., Ban, J. O., Park, H. K., … & Hong, J. T. (2009). l-Theanine, an amino acid in green tea, attenuates β-amyloid-induced cognitive dysfunction and neurotoxicity: reduction in oxidative damage and inactivation of ERK/p38 kinase and NF-κB pathways. Free Radical Biology and Medicine, 47(11), pp. 1601-1610. (article).
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