Theanine: The Beneficial Amino Acid Found Only In Tea

L-theanine acts on the brain in ways that can make you calm and happy.

Photo: © Mary Ann Rollano

“Plants know how to make food and medicine from light and water, and then give it away.”

— Robin Wall Kimmerer, Braiding Sweetgrass

Have you ever wondered why tea drinkers always seem so calm? A cup of tea can lift mood, improve focus, reduce anxiety, and perhaps ward off dementia.

Tea contains a unique combination of caffeine and theanine (l-theanine), a non-protein amino acid. Theanine may be the best-kept secret behind tea drinkers’ calm happiness.

These two ingredients have an extraordinary effect on the brain. Theanine has a very calming effect, while caffeine is a stimulant. Theanine modulates the caffeine, reducing its jittery effects and creating a calm and focused state of mind.

I’m referring to the Camellia sinensis plant’s black, green, white, and oolong tea. This tea differs from herbal tea, an infusion made from any other plant called tisanes.

Of all the thousands of plants to choose from, why is this one tea plant the most popular beverage in the world? It’s not the caffeine. The coffee plant has more caffeine, but more people drink tea worldwide than coffee. 

Why do we drink millions of cups of tea a day?

Theanine in tea

The tea plant contains an amino acid only found in two natural places: tea and a rare mushroom called the bay bolete. Scientists have identified this rare and unique amino acid as theanine.

What exactly does theanine do that has millions of people drinking tea?

Researchers sought to answer this very question. The Brain and Cognition Laboratory at Oxford University in the UK studied¹ the ability of theanine to induce a relaxed, alert mental state.

Participants were connected to an electroencephalogram (EEG) to measure their brain wave activity—specifically their alpha wave production.

A brief overview of human brain activity

Humans have four primary mental states, as measured on an EEG. Brain waves are measured in hertz (symbol: Hz) in the International System of Units (SI). One hertz is equivalent to one cycle per second.

Two sleeping states:

1. Delta waves occur when the entire electrical brain activity cycles slowly at about one wave per second during deep sleep. They have a frequency range of 1 - 4 Hz.

2. Theta waves occur during dream sleep and deep relaxation and cycle at about five waves per second. The frequency range is  4 - 8 Hz.

Two waking states:

1. Alpha waves are present in a relaxed, aware, and attentive state, similar to a meditative state. Their frequency range is 8 - 12 Hz.

2. Beta waves dominate during the stimulated hustle and bustle state, where we spend most of our waking lives. The frequency range is 13 - 30 Hz.

The alpha state is where you want to be - fully alert and calm. But how do you get there?

If you relax in a lovely, peaceful place after about 90 minutes, you can see a significant increase in alpha brain waves. Think of a quiet afternoon at your favorite beach or a pleasant long nature walk at sunrise.

Meditating Buddhist monks can achieve this state sooner and maintain it with open eyes. So you can meditate daily for a few years or drink some tea.

This is your brain on tea

The study team from Oxford noted:

“L-theanine significantly increases activity in the alpha frequency band which indicates that it relaxes the mind without inducing drowsiness.”

The Oxford study participants rested with their eyes closed during EEG recordings of their alpha brain wave activity.

The amount of theanine that enters your brain, crossing the blood-brain barrier after drinking two cups of tea, is about 50 mg. Look at the effects of l-theanine after drinking the equivalent of two cups of tea.

The orange area is the presence of alpha wave activity. See the difference?

Image source: Republished with permission. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr 2008;17 (S1):167-168

Can a cup of tea reduce anxiety?

I asked some of my readers about their experience with theanine in tea, whether they found it beneficial, and in what ways. 

In an e-mail interview, Wendy says she likes drinking tea and meditating. She says it’s the “perfect combination.” Wendy explains,

“My husband has a depressive disorder, and drinking tea helps sort him out; (he) feels relaxed and a little more positive after.”

Wendy and her husband’s positive experience with drinking tea is quite common. Another reader shares her experience,

“I have anxiety, panic disorder, and ADHD so that I can share my experience. It kinda helps with ADHD by slowing down my mind a bit, but I didn’t experience much else.” It can help with mild anxiety and possibly prevent a panic attack if you catch it soon enough, but it barely helps bad anxiety for me. I would encourage people to try it, though, because everyone is different, and they might have a profound benefit from it.”

Tea for anxiety

Michelle Francl, author of Steeped: The Chemistry of Tea, writes,

“Studies have shown that theanine can reduce anxiety, improve cognition, reduce blood pressure, improve the quality of sleep, and, like caffeine, has neuroprotective properties...”²

This is because theanine crosses the blood-brain barrier and affects the central nervous system.

This increase in alpha activity supports theanine’s role in achieving a relaxed mental state by directly influencing the central nervous system. Combining theanine with caffeine makes tea a unique beverage that promotes mental focus, increases energy, and reduces anxiety and stress.

Clinical trials³ have shown that theanine reduces anxiety and induces calm because it increases the neurotransmitters that balance our moods and controls serotonin and dopamine, making us feel good.

Another study, published in 2020 in Plant Foods for Human Nutrition⁴, reviewed available data on theanine's effects on cognition and mood in humans and evaluated its impact on anxiety and stress.

The researchers found that theanine can reduce the stress response in people with mild anxiety. However, it is not as effective in lowering clinical-level anxiety.

The effective doses reported in the 2020 review of studies range from 200 to 400 mg. The Oxford study used only 50 mg of theanine and saw a difference in alpha brain wave activity. Depending on the tea and the brewing process, a cup of tea can have anywhere from 8 to 46 mg of theanine per cup.

Benefits of theanine in tea

Scientific evidence in these studies suggests that drinking tea provides many theanine benefits:

• Increased cognitive function. Tea may protect our brains. The American Journal of Clinical Nutrition⁵ shows that regular tea consumption is associated with lower risks of cognitive impairment and decline. 

• Lower blood pressure. The Journal of Physiological Anthropology⁶ reports that theanine reduces anxiety and lessens the blood pressure increase in high-stress-response in healthy adults.

• Improved mood. The University of Oxford study showed that theanine in tea elevates mood, reduces stress, and promotes relaxation. 

• Increased alertness. The same Oxford study showed that theanine balances the stimulatory effects of caffeine so you stay alert without feeling jittery. 

• Improves attention span. A study published in Nature⁷ showed the natural combination of theanine and caffeine may result in short-term improvements in concentration and overall cognitive performance among boys with ADHD (attention deficit hyperactivity disorder). 

How much theanine is in a cup of tea?

Certain teas have higher amounts of theanine than others. Green teas, grown in the shade for three weeks before harvest, have some of the highest theanine levels.

The shading increases the plants’ chlorophyll levels and the production of theanine uptake from the root system simultaneously.

Shade-grown green teas include matcha, gyokuro, and tencha. The abundance of theanine adds sweetness, earthiness, and umami to green tea.

“Growing conditions affect the amount of theanine produced in a given tea plant. Teas grown in sunnier conditions produce less theanine. First flushes will have more theanine than later flushes because the theanine that has spent the winter stored in the roots is transported to the early shoots, leaving less for sprouts that appear later in the season.”

Michelle Francl, Steeped: The Chemistry of Tea

Brewing time is a significant factor in the amount of theanine extracted. The type of tea leaves used may provide different amounts of theanine and caffeine. Food Chemistry⁸ reports that adding small amounts of milk and sugar makes no significant difference. 

• Theanine in Black tea: A standard 6-ounce cup contains 24.2 milligrams of theanine. 

• Theanine in Green tea: A cup of green tea contains at least 7.9 milligrams of theanine. 

• Theanine in Shade-grown green tea⁹: Matcha and Gyokuro may have as much as 46 milligrams of theanine per cup. 

Are theanine supplements beneficial?

You can buy theanine supplements over the counter at 100 mg per tablet. Because the tablets are caffeine-free, some people take them to relax before sleep.

But the magic lies in the tea rather than pure theanine. Tea contains many different chemicals, all acting synergistically with one another. You know, a lot is going on in that little tea leaf when someone can write an entire book on the chemistry of tea.

Isolating the active chemical elements from natural remedies is equivalent to capturing the information but discarding the wisdom. Nature is designed to take the whole leaf, not isolate the chemical components, for its remedy.

Positive theanine effects

Perhaps many people choose tea over coffee to reach that calm, alert alpha state of mind. Or maybe they do it to reduce anxiety with the calming effects of theanine on the brain. It doesn’t matter if you drink tea for anxiety or happiness; there are many positive benefits.

There are so many reasons to drink tea. It's no wonder it has been used as a restorative beverage in traditional Chinese medicine for thousands of years.

How about you? Do you experience theanine's calming and focused effects if you drink tea?

1. Nobre, A. C., Rao, A., & Owen, G. N. (2008). L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pacific journal of clinical nutrition, 17 Suppl 1, 167–168.

2. Francl, M. (2024). Steeped: The chemistry of tea (1st ed.). Royal Society of Chemistry.

3. Nathan, P. J., Lu, K., Gray, M., & Oliver, C. (2006). The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. Journal of herbal pharmacotherapy, 6(2), 21–30.

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7. Kahathuduwa, C. N., Wakefield, S., West, B. D., Blume, J., Dassanayake, T. L., Weerasinghe, V. S., & Mastergeorge, A. (2020). Effects of l-theanine–caffeine combination on sustained attention and inhibitory control among children with ADHD: A proof-of-concept neuroimaging RCT. Scientific Reports, 10(1), 1-13. https://doi.org/10.1038/s41598-020-70037-7

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