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theanine is an amino acid found in tea leaves

Your guide to theanine

23 Nov 2022 • 2 min read

Here you will find out just what theanine in your brew can do – you won’t think of tea in the same way again.

What is theanine?

Discovered by Japanese scientists in 1949, theanine is an amino acid that is most commonly found in tea leaves. It's also known as l-theanine. 

However, it's also known to be found in some mushrooms and green tea but is otherwise rare in nature.

Theanine is available as a supplement, with a recommended dosage of 200mg per day.

L-theanine is known to help:

  • Relaxation
  • Focus
  • Sleep1

Other evidence suggests, that when consumed in tea, theanine may change taste perception. Specifically, by lowering the bitter taste in foods such as chocolate and grapefruit.2 


  • Theanine is a unique amino acid found in tea leaves
  • It's known to help improve relaxation, focus and sleep
  • It was discovered by Japanese scientists in 1948 and can also be found in some mushrooms and green tea.
  • Other evidence suggests that it can change taste perception.

What does l-theanine do?

A nice cuppa is known to help you relax. But there are many other potential health benefits that you might not know about theanine.

Here you will find four ways that theanine can improve brain function and imrpove sleep.

Four benefits of l-theanine

  1. Keeping focus and attention: When paired with caffeine, theanine may help enhance focus and attention. A 2013 study3 noted that a combination of 97mg of L-theanine and 40mg of caffeine significantly improved accuracy when switching between different tasks.
    L-theanine may help improve accuracy and a reduction in the number of errors made in a test of attention. The combinations of L-theanine and caffeine may improve attention span, enhance the ability to process visual information, and increase accuracy when switching from one task to another.
  2. Supporting good sleep: with the ability to improve relaxation and lower stress levels, l theanine can also have a positive impact on your sleep. By promoting the levels of relaxation, it's thought that l theanine can help you fall asleep more easily, without acting as a sedative but by relieving the mind from stress.
    As a natural sleep remedy, l theanine and lemon balm are often overlooked. Both are seen as natural remedies to can be used together to help improve sleep hygiene.
  3. Help maintain a healthy weight: l-theanine may not help you lose weight directly. However, the relaxation qualities and ability to maintain stress levels, along with a healthy balanced diet can protect against weight gain.
    After all, enough sleep, keeping on top of your health and wellbeing, along with eating healthily can be only be a good thing.
  4. Clearing sinuses: Who knew that something as simple as a cup of tea could help with your sinuses? The Grossan Sinus & Health Institutenotes that l theanine can help improve the performance of the hair-like fibres in your nose that help clear mucus, known as cilia.

Does l-theanine make you happy?

It’s unlikely that the consumption l theanine will make you happy. However, when you take the above factors into consideration, it may be that you see improvements in your overall wellbeing. After all – feeling relaxed, getting enough sleep and a healthy diet will definitely help.


  • When mixed with caffeine, theanine can help improve focus and attention when switching between or concentrating on difficult tasks.
  • Known as an anxiolytic – theanine has a relaxing effect without being a sedative like other anxiolytics
  • The relaxation qualities of l-theanine are known to help sleep hygiene.
  • Theanine may not directly help weight loss, but its overall qualities to increase relaxation and sleep, paired with a healthy diet can see you maintain a healthy weight.

How does theanine work?

Now you know what theanine does, its probably best you know how it works.

We know that it stimulates relaxation, which helps contribute to better sleep, but how does l theanine contribute to making those changes in the brain?

Three ways theanine helps your brain

  1. Increase calming brain chemicals

L-theanine works by raising Gamma Aminobutyric Acid (GABA)5 as well as serotonin and dopamine in the brain. These are chemicals in the brain, known as neurotransmitters, that help you control your cognitive skills.

By Increasing levels of these calming brain chemicals, you can help promote relaxation and improve your sleep.

Neurotransmitters help regulate your:

  • Emotions
  • Mood 
  • Concentration
  • Alertness
  • Appetite
  • Energy
  1. Lowers levels of excitant brain chemicals

This doesn’t mean that you are less likely to feel excitement, but l theanine may reduce and help anxiety by balancing the chemicals in your brain that are linked to stress. It is thought that this may also be a way that l theanine can help protect ageing brain cells.

  1. Attentive relaxation

L-theanine releases alpha brain waves. Alpha brain waves are the state of mind you reach when meditating, being creative or letting your mind go when daydreaming. They also occur when you reach a state of REM when sleeping.

This can make l-theanine an attractive choice for people who are looking to enhance their “wakeful relaxation,” without worrying about becoming fatigued.


  • L-theanine is a neurotransmitter, which help control your cognitive skills.
  • Chemicals in your brain linked to stress and anxiety may be regulated through l theanine’s relaxing components.
  • Alpha brain waves that occur at moments of relaxation are released when l theanine is present  

What is theanine serene used for?

As mentioned above, l theanine is a unique compound found in tea that has many relaxing qualities that helps aid concentration and sleep.


  • L-theanine helps aid relaxation, concentration, and sleep

What are the best sources of l theanine?

Tea is the main source that we consume l-theanine as it doesn’t particularly occur naturally in many other foods.

As we all know, making a cup of tea is common practice. Although it probably goes without saying that how you prefer your tea is entirely down to your own taste and always a good debate! This can also determine the amount of l theanine you are getting in your cuppa.

Brewing time and amounts of milk can determine how l-theanine we receive.6 For a standard cup of tea (200ml) you are likely to consume:

  • Black tea (contains the most l theanine: 24.2±5.7mg)
  • Green tea (contains the least l theanine: 7.9±3.8mg)

L-theanine is also found in the boletus badius mushroom, although it's not clear exactly how much or how many you would need to use to make it beneficial without more detailed research.


  • Tea is the most common way of using l-theanine, however, it’s hard to quantify exactly how much.
  • Black tea is seen as the largest amount of l theanine with 24.2±5.7mg. while green tea contains the least with 7.9±3.8mg
  • L-theanine is found in the boletus badius mushroom, however without more detailed research, it's difficult to know how many you need to make it beneficial.

L-theanine risks and side effects

Generally, there are no side effects to l theanine and its safe for healthy adults to take supplements and drink teas that contain l theanine.

What is a safe daily intake?

Most l theanine supplements contain around 200mg, but there is no conclusive research that says just how much you should have. Drinking tea is generally safe for most people, and there have been no reports of overdose or side of affects of l theanine.

However, it’s worth keeping in mind that many l theanine supplements may contain caffeine, so its worth following the same guidelines as caffeine (400 mg)7.

Like caffeine, it is thought that if you consume excessive amounts of l theanine you may experience:

  • Nausea
  • Upset stomach
  • Feeling irritable

It would be considered best practice to consider your l theanine intake and consult your doctor if you are:

  • Pregnant or breastfeeding
  • Have low blood pressure
  • A child under 16


  • Generally, for healthy adults there are no known side effects of l theanine.
  • Drinking tea is and l theanine caffeine supplements are known to be safe, however its probably safest to follow the same guidelines as caffeine (400mg per day)8.
  • Extreme amounts could cause sickness
  • If you’re pregnant, have low blood pressure or have any concerns then you should consult your doctor.

What’s the bottom line with l-theanine?

There is some evidence to suggest that l theanine can benefit your mental and physical health. However, more scientific research is needed before it can be proven just what effects the amino acid l theanine has.

Last updated: 27 April 2021



Author: Bhupesh PanchalSenior Regulatory Affairs Associate

Joined Holland & Barrett: Apr 2019

Masters Degree in Toxicology and BSc Hons in Medical Biochemistry

Bhupesh started his career as a Clinical Toxicologist for Public Health England, advising healthcare professionals all around the country on how to manage clinical cases of adverse exposure to supplements, pharmaceuticals, cosmetics, industrial chemicals and agricultural products.

After 7 years in this role and a further year working as a drug safety officer in the pharmaceutical industry, Bhupesh joined Holland & Barrett as a Senior Regulatory Affairs Associate in 2019.

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