L-Theanine: Dosage, Dangers, And Benefits For The Brain.

Tea awakens the mind and wise thoughts. It refreshes your body and calms your mind. If you are depressed, tea will give you energy”. These words were spoken by the legendary Chinese emperor Shennong to describe the most commonly consumed beverage in the world after pure water.

Since time immemorial, tea drinkers have benefited from both the invigorating and calming effects of tea, although this may seem contradictory at first glance.

While the stimulating effect is due to caffeine, the relaxing effects are attributed to the amino acid theanine contained in black and green tea. The question is no longer: theine or caffeine, but theanine or caffeine. What should we think?

Discover our complete guide on L-Theanine, this natural nootropic!

Presentation Of L-Theanine.

L-theanine is an amino acid that has many benefits for the brain. This product is extracted from the tea. It is consumed to calm stress, promote sleep and concentration. 

Tea And L-Theanine.

L-theanine was first isolated and identified in 1949 by the Japanese researcher Y. Sakato. This amino acid is extracted by the hot water of the infusion in a few moments. After one minute, more than 50% of the total extractable theanine is already in solution. L-theanine is a colorless, water-soluble, non-proteinogenic amino acid that co-determines the taste of the beverage tea. 

Theanine is present not only in Camellia sinensis but also in Camellia japonica and sasanqua species. It is synthesized in the roots of the tea plant from glutamic acid and ethylamine by theanine synthetase, then transported to the leaves, where it is stored. Together with glutamine and other free amino acids, theanine forms the non-protein component of the plant.

The best way to consume the amino acid L-theanine is therefore to drink tea. However, it is now available in capsule form containing extracts. Faced with the restlessness of the modern world, laboratories specialized in food supplements have indeed wished to offer this health product even to those who do not drink tea, because of its benefits on the brain and its health potential.

How Does L-Theanine Work?

Scientists have discovered that L-theanine in tea is the counterpart of caffeine. Caffeine stimulates the mind, but it also has side effects that can be unpleasant for people who are intolerant to it. In high doses, the substance can cause palpitations, inner turmoil, insomnia, and increased blood pressure. 

This is where L-theanine comes in, which is supposed to be able to neutralize the negative effects of caffeine. What happens is the often described effect of green tea: it wakes you up gently, is not as stimulating as coffee, and relaxes you at the same time. A win-win situation for the tea drinker.

In a study by the University of Shizuoka in Japan, it was shown as early as 1999 that L-theanine stimulates alpha waves in the brain. This product allows you to relax, but without causing drowsiness. Scientists have stated that L-theanine and therefore the consumption of green tea have a stress-reducing effect. 

In addition, they recalled some previous studies on rats, which had shown that L-theanine had a positive effect on the learning performance and memory of the animals. Another study conducted in Japan in 2006 confirmed the relaxing effect of L-theanine on humans.

Theanine can cross the blood-brain barrier and is similar to the proteinogenic amino acid L-glutamine, which is decarboxylated in the central nervous system by the enzyme L-glutamic decarboxylase to γ-aminobutyric acid (GABA), an important neurotransmitter. 

Effect On Neurotransmitters.

Various animal studies have shown that L-theanine affects the levels of various neurotransmitters in the brain. For example, intraperitoneal administration of 1740 mg/kg of L-theanine produced a decrease in norepinephrine levels. An increase in brain dopamine concentration was also observed with theanine administration.

The results of research on the effect of L-theanine on serotonin levels are contradictory.  In any case, it is widely accepted that theanine counteracts the central stimulant effect of caffeine. Some researchers also believe that theanine increases the production of GABA.

It is also now known that theanine stimulates the frequency of alpha waves, which has been demonstrated through medical imaging and electroencephalograms. It thus induces a very particular form of relaxed vigilance.

What Diseases Can L-Theanine Treat?

Data on the effects of L-theanine on humans is extremely incomplete. Theanine is believed to have various effects for which there is no evidence. It is believed to reduce the symptoms of premenstrual syndrome and anxiety disorders. 

A study of 14 male student-athletes found that high doses of theanine after exercise were associated with lower prolactin levels and improved electroencephalogram values. Another study also describes the increased generation of alpha waves in female subjects after oral administration of 200 mg theanine.

Relaxing Effects.

The natural amino acid extracted from the tea plant causes a feeling of calm and relaxation by stimulating alpha waves in stressful situations, without necessarily leading to sleep. Consumption in the evening improves sleep quality, but only because it is easier to sleep in a relaxed state. 

Moreover, L-theanine has nootropic properties: it can have a positive effect on our state of mind and sharpen attention and concentration. The combination of L-theanine and caffeine is particularly recommended, as L-theanine slows down the negative side effects of caffeine while allowing for greater concentration.

The Chinese emperor Qianlong (1711-1799) recommended “tea against the noise of the world”. He recommended the following recipe: 

“Fill a vessel with the clear water of melted snow, let this water be heated to the point that the fish becomes white and the crab red, pour this water into a cup over thin leaves of selected tea, let it stand for a little while until the first vapors, which form a thick cloud, gradually diminish and only light mists float to the surface. Drink this delicious potion, then, and you will act powerfully against the five pains which commonly trouble our minds.”

Better Stress Management. 

Tea contains three main active substances: caffeine, catechins, and L-theanine. L-theanine helps to reduce blood pressure, which makes it an excellent ally in stressful situations. The particularity of theanine is that it promotes relaxation, but without clouding the mind, which remains alert and focused. 

It is therefore the ideal amino acid for those who want to meditate. In any case, the health benefits of theanine are not limited to the brain. The product could reduce the reactions of mental stress, but also physical. Nevertheless, it is difficult at the moment, and in the absence of decisive studies, to differentiate the effects of theanine itself from those of other substances contained in tea.

Thus, the use of high doses of theanine in vitro, animal, or human studies has nothing to do with the effects that can be obtained by drinking tea. 

Main indications of L-theanine: 

  • Stress.
  • Difficulty falling asleep.
  • Agitation.
  • Anxiety.
  • Difficulties concentrating.

Dosage: How To Use This Treatment?

As we have seen, the most pleasant way to absorb L-theanine is to drink tea. People who do not appreciate this beverage and those who have an increased need for theanine, which simply drinking tea cannot satisfy, can turn to capsules, tablets, or capsules manufactured by laboratories specialized in food supplements.

In this case, it is advisable to take the tablet with a large glass of water, to optimize its absorption. If you are looking for an effect on sleep, take this amino acid one hour before going to bed.


There is no risk of overdosing on theanine if you drink tea. A dose of 50 to 200 mg per day is generally considered safe for humans. However, the only available studies on the potential toxicity of this amino acid at high doses have been in rats. 

By extension to humans, it seems that theanine poses a problem from 2 grams per day. Taking theanine is not recommended during pregnancy or breastfeeding. People who consume theanine by drinking tea have a fairly low intake, well below the doses studied.

For example, the Japanese, who are heavy tea drinkers, only consume 20 mg of theanine per day through tea. 

The exact duration of intake depends on the desired effect. The 200 mg intake is particularly suitable in the morning in combination with the morning coffee in order to start the day concentrated and relaxed. 

However, L-theanine can also be taken at other times of the day, for example, to calm down in stressful phases or in situations where you need maximum concentration. 

For better sleep, however, 200 mg of L-theanine is recommended about 30 minutes to an hour before going to bed. 

L-theanine tablets can be stored at room temperature and consumed up to the expiration date on the package.

Risks And Dangers Of This Amino Acid.

Undesirable Effects.

L-theanine is an amino acid that is not well studied and therefore not well known. The question of possible side effects naturally arises. To date, research has not shown any undesirable effects when theanine is taken at a reasonable dose, 1 to 2 times 200 mg per day. 

Nevertheless, as this product regulates blood pressure, a feeling of dizziness can sometimes be felt, if you consume too much. Simply reduce the dose.

Drug Interactions.

Treatment Of Hypertension.

L-theanine causes an increase in antihypertensive drugs.

Antagonistic Effect Of Caffeine.

As we have already seen, theanine balances the arousal effect induced by caffeine.

Sedative Treatment.

L-theanine potentiates the effect of common sedatives.

Interaction With Doxorubicin.

L-theanine decreases the cardiotoxicity of doxorubicin.

Opinions On L-Theanine.

Most people who take L-theanine find that it improves their sleep and calms their anxiety.

However, theanine seems to work less well for others.

Buying Guide.

Always remember to choose a reliable source for your dietary supplement purchases. If in doubt, choose a pharmacy or an online pharmacy, consult your doctor or ask your pharmacist for advice.

As we have seen in this article, L-theanine remains a somewhat confidential food supplement in France. However, its benefits on concentration and sleep are real. It may be necessary to buy it online, on the pages of a specialized store, or on Amazon.

You can also find L-Theanine in the nootropic Noocube!


Can L-Theanine Be Combined With Other Medications To Promote Sleep? 

Yes, but be careful with sleeping pills, whose effects are potentiated by theanine. Melatonin is preferable.

Can We Supplement By Drinking Tea?

Yes, you can. But the effect will be more subtle and progressive. It is necessary to drink a large quantity of tea, throughout the day, as is the custom in Asian countries.

Should I Choose Organic Theanine?

Yes, preferably, but this is not always possible, especially if you consume this amino acid as a dietary supplement. On the other hand, there are some very good organic teas available today, which should be preferred.

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