Cognitive Effects of L-Theanine

Updated: Nov 16

Tea leaf (lat. Camellia Sinensis) has been a favoured as a warm drink for thousands of years especially in ancient eastern civilisations. The benefits of it have gradually attracted the attention of the public and nowadays, green tea in particular more than black or white tea, has become one of the most popular warm drinks on the planet

In this article, I'll run through some interesting findings on L-Theanine from different research across the world. I was surprised by the amount of available studies. Some of them have even used things like MRI or electroencephalographs to observe real-time response of neurons in the central nervous system.

Green tea contains several major constituents:

  • Caffeine – a commonly consumed stimulant of the central nervous system

  • Catechins – of which the major one is epigallocatechin gallate (EGCG)

  • Gamma-N-ethylglutamine - more commonly known as L-Theanine

[FOR THE NERDS] Skip if not interested in the mechanisms

Caffeine is a known stimulant of the central nervous system. It crosses the blood-brain barrier and docks into receptors for a protein called Adenosine that gradually accumulates through the day, causing progressive tiredness and sleepiness as the day goes on. Through this action, it blocks the signal of Adenosine and induces a state of alertness temporarily (until caffeine is detoxified). Caffeine also stimulates cortisol and adrenaline from the adrenal glands, an effect responsible for the "caffeine kick".

We don't know as much about catechins & EGCG as we do about caffeine. A lot of what we know comes from in-vitro studies. EGCG is a powerful antioxidant that can block specific inflammatory processes in the body and may even slow certain pro-carcinogenic processes inside the cell of a human body. EGCG has also been found to improve the circulatory function of the blood vessels by increasing the supply of nitric oxide.

L-Theanine appears to work through several mechanisms, including alpha-wave stimulation, direct influence on the executive regions in the brain, stimulation of GABA (calmness-inducing neurotransmitter) and serotonin (happy hormone).


In 2006 an observational study from Japan had shown that people who regularly consumed green tea (>2 cups/d) had fewer strokes, lower blood pressure, less diabetes, better physical vigour. They also had reduced the occurrence of dementia or other forms of cognitive decline.

In 2007 another Japanese observational study on 2845 people found that those who drank green tea daily had the lowest incidence of dementia and mild cognitive impairment (MCI) compared to those who did not drink it.

Both of these have spurred a large amount of subsequent investigation. New studies started looking into individual components of green tea, one of which was L-Theanine (LT). LT is a non-proteinogenic amino acid (not part of larger protein molecules) that has been discovered way before these two studies happened, but the majority of the research on this one particular molecule started after 2007.


It appears the primary goal of these studies was to find out if and how LT influences the human brain and its performance. Several randomised studies using LT and placebo have been conducted, and some interesting results came up.

One of those was a combined study from USA, Sri Lanka and Australia where subjects were put under the functional magnetic resonance imaging (fMRI) observation after having consumed a solution of 200mg LT alone or in combination with a placebo. This is what they found

  • LT reduced the activity in the part of the brain that becomes activated when the mind wanders. This may mean that L-Theanine enhances the ability to focus on a single task, potentially being useful for people with ADHD or ADD

  • There was also a decrease in activity in the region responsible for processing visual stimuli. This could potentiate the so-called "tunnel effect" where multiple visual distractions are no longer registered by the brain and brought to present attention.

  • When particular visual stimuli were introduced to the subjects to which they had to react (press this button when you see this light), their reaction time improved.

An interesting finding in this particular trial was that when LT was combined with caffeine (160mg), the reaction time to the stimulus was faster than in LT-only group. However, the activity in the brain region called Anterior Cingulate Cortex was reduced. This region is partially responsible for sustaining attention, error detection, executive thinking, automated behaviour and pattern recognition. What this could mean that while LT alone may help with concentration and easier focus on task, when caffeine is added, some of this benefit is lost, mind becomes a bit more jittery. However, the addition of caffeine may be helpful in tasks or sports where reaction speed is more important than sustained focus.

Another study where researchers put a device called an electroencephalograph (EEG) on people's heads to monitor the nerve impulses in their brain after drinking a solution with LT found an increase of activity in the region responsible for selective attention. This effect was attenuated by the addition of caffeine.

A small Japanese study on 68 men supplementing them wither with a product called Suntheanine or placebo for 12 weeks found:

  • faster reaction time and improvement of working memory

  • increased correctness of answers and decreased omission or errors.


The human brain functions on a regular electrical activity called neural oscillation, a rhythmic and regular pattern inside the neurons either in a particular region or in single neurons. This activity changes depending on the environment, time of the day but also based on mood, activity and exposure to certain external factors.

A particular pattern called Alpha-Waves activity that is often found during meditation, relaxation or in a state of calmness has been connected to LT in some theoretical studies.

In 2007 this was put to the test when a small 15-participant study divided participants into L-Theanine group and placebo group randomly. After conducting an EEG scan on all of them, the researchers observed an increased alpha-wave pattern in those in LT group. While the results were not profound, this was the first study that demonstrated a change of wavelength pattern in certain parts of the brain after LT consumption.

This effect was also noted in another study using a combined drink of LT, L-alpha glyceryl phosphorylcholine (alphaGPC) , chamomile extract and pahosphatidylserine. Participants had increased levels of alpha brain wave activity and reduced levels of the stress hormone cortisol, 3-hours after the test compared to the placebo group.


Only two studies looked at the efficacy of LT in depression.

A small German study on 30 individuals found that those who took L-theanine for 4 weeks had a decent improvement of their self-rated anxiety, depression and sleep scales.

In the second study, LT was mixed in a complex of bacopa monieri, saffron, B-complex and copper. Subjects in this study had some mild improvement in their depression & mood; however, the difference was not profound when compared to the placebo group. In this study, it was also possible that the anti-depressive effect could have been driven by saffron rather than LT as saffron has known clinical benefits for people with depression even when compared to pharmaceutical antidepressants.


A little more studies have been done on people with Anxiety (GAD – Generalised Anxiety Disorder); however the majority of the results show little to no benefit of L-Theanine.

In one particular study, 36 healthy people were randomised into placebo and active group. The active group had received a liquid solution containing LT (200 mg) , L-alpha glyceryl phosphorylcholine (alpha GPC; 25 mg), phosphatidylserine (1 mg) and chamomile extract (10 mg). Participants had their stress levels and fatigue assessed as well as salivary test for cortisol (stress hormone) before and after. In the bigger picture, however, this one study is not sufficient proof that L-Theanine is useful for anxiety as some of the other components used could have contributed to that effect. Chamomile, for example, has well documented anti-anxiety effects in humans and animals.

Overall, L-Theanine has a mild effect on anxiety at best. The studies are not conclusive, and where there is an effect, it is mild. Combined with other products, the effect may be more profound.


  • L-Theanine is a component found in the green tea along with EGCG and caffeine.

  • L-theanine has shown some improvements in focus to a single task as well as a reduced rate of distractibility and more calmness

  • L-Theanine has been shown to increase the ratio of alpha waves in the brain, commonly seen in meditators or when the body is relaxed and calm.

  • L-Theanine may have mild effects on depression and stress ; however, it has not been particularly useful in anxiety.

  • L-Theanine is safe to take a supplement that has no interactions with drugs and might be worth the experimental investment. A product called SunTheanine has been shown to be very pure and reliable. The company has also conducted their own research. This claim was made without any financial bias.

  • Doses between 100-200mg per day seem to have the best effect

  • L-Theanine may be used alongside caffeine however some of its benefits may be lost due to simulative effect of the later

Do you experience regular brain fog and concentration issues? Would you like to think clear again?

Maybe I can help. My name is Michal, I am certified holistic nutritional therapist specialising in brain health, mental health, energy metabolism & gut health. It would be my pleasure to have a free chat with you and see if I can offer any advice or tips. You can book a free call with me by following this link. I have worked with other men experiencing brain fog and energy problems and helped them feel awesome again.

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Baba, Y. et al. (2021) ‘Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study’, Journal of Medicinal Food, 24(4), pp. 333–341.

Camfield, D. A. et al. (2014) ‘Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: A systematic review and meta-analysis’, Nutrition Reviews, 72(8), pp. 507–522.

Cicero, A. F. et al. (2017) ‘Short-Term Impact of a Combined Nutraceutical on Cognitive Function, Perceived Stress and Depression in Young Elderly with Cognitive Impairment: A Pilot, Double-Blind, Randomized Clinical Trial’, The journal of prevention of Alzheimer’s disease, 4(1), pp. 12–15.

Gomez-Ramirez, M. et al. (2007) ‘The deployment of intersensory selective attention: A high-density electrical mapping study of the effects of theanine’, Clinical Neuropharmacology, 30(1), pp. 25–38.