Health coach Phillippa Quigley takes a look at what L-Theanine is, how it can be beneficial to our mind and body, and where to find it.

L-Theanine featured image
Phillippa Quigley headshot

Last Updated:

Written by Phillippa Quigley – fact checked by Jason M & the editorial team

Phillippa is the owner and founder of Health and Soul and coaches and supports clients in the field of women’s health, nutrition, stress management, lifestyle, mindset, weight loss and general fitness. She is a valued writer here at SOMA Analytics and assists with our editorial content.

This article complies with the SOMA Analytics editorial policy. Full details of which can be found here

Theanine is a non-protein amino acid that was discovered by scientists in Japan, in 1949. Also know as L-theanine, it is commonly found in tea leaves. 

In this article we will discover the benefits of Theanine, its natural sources, as well as supplementation. 

What Is Theanine?

Theanine is mainly found in green and black tea, as well as mushrooms. Other than those sources it is thought to be rare.

There are two forms of Theanine; L-theanine and D-theanine. D-theanine does not occur naturally in foods, whereas L-theanine does, and is safe for human consumption. 

Theanine is thought to have many health benefits, including providing improved cognitive function. Theanine increases calming neurotransmitters in our brains.

It is popular for helping people relax. Theanine is known for easing anxiety and stress, and reducing insomnia. All of these symptoms collectively would be effecting a person’s mental health and ability to carry out normal day to day activities efficiently.  

How Does Theanine Benefit Us?

Formally known as L-g-glutamylethylamide; L-theanine gets absorbed through your small intestine. It delivers protective effects to your nerve cells.

We now know that Theanine has a calming and relaxing effect on our body. Let’s take a more detailed look at more of the effects of Theanine.

Focus and Attention

If you pair Theanine with caffeine, it is thought to improve your focus. A small study was able to show that pairing the two helped people focus better when carrying out a demanding task. It also enhanced their accuracy when switching around between tasks. Theanine with caffeine also helped reduce the amount of errors made.

When combining Theanine and caffeine it can increase your attention span and the ability to process information. In the small study, participants felt that they were less tired and more alert. 

Stress Relief

When you stop to have a cup of tea, it is often a moment that you can feel a temporary relief from a busy day. The hot tea helps us feel relaxed and soothes our body. This can help relieve stress and anxiety. 

Theanine is thought to counter balance the stimulation effect from caffeine, which is where the relaxation and calming effects comes from. It isn’t fully understood how Theanine helps reduce anxiety, but we know it increases the levels of two neurotransmitters responsible for altering our mood; Serotonin and Dopamine.

L-theanine also increases the production of GABA. GABA being; Gamma-Aminobutyric Acid. GABA has a calming effect on your body by blocking or inhibiting brain signals that would normally be triggering fear or stress. 

If you choose a tea that is rich in Theanine, this may help you feel less stressed and reduce your anxiety. Therefore, if you are a tea drinker already, you could think about changing your usual tea habit to either black tea or green tea. 

Green tea is known for many other health benefits such as:

  • High in polyphenols (Polyphenols are compounds from plant sources that are packed with antioxidants which protect our body from stress and disease.)
  • Natural stimulants that support brain function i.e; caffeine.
  • Boost metabolism
  • Blood sugar control
  • Lowers risk of heart disease


Including Theanine in your diet can reduce insomnia. By reducing stress levels and helping yourself to relax, you will naturally be able to sleep better. 

With the relaxing effects Theanine can have, it is thought to improve your quality  and length of sleep. L-theanine achieves this not be acting as a sedative but through its effects of stress relief and relieving the mind. 

If we are in a more relaxed state and not feeling stressed, it improves our overall sleep hygiene. When we suffer with insomnia, we tend to already feel stressed about the night’s sleep ahead, which then contributes towards a poor sleep routine. 

There are lots of calming ‘sleep’ products around that include Theanine to help promote a good night’s sleep. Always check the list of ingredients before you try them – you don’t want to be consuming something that is packed with artificial ingredients. 

Blood Pressure

When we are stressed and involved in a high demanding, stressful situation, our blood pressure will rise. A study revealed that when people had completed high-demanding mental tasks, Theanine helped their blood pressure decrease if it had increased within the task.

Due to the calming effects Theanine has, it has been said that it can help with reducing a resting heart rate. 

Theanine could be beneficial for individuals who suffer with increased blood pressure. It has been found by Japanese researchers that Theanine can reduce high blood pressure for those with a pre-existing problem. For example, someone who is suffering with hypertension. 

If you are already on medication for blood pressure management, you would need to be careful before consuming Theanine. For further support with this, you would need to contact your healthcare provider. 


Theanine can improve your body’s immune system. Teas containing theanine have been found to decrease the chance of infection. 

Green tea in particular is known for strengthening the immune system.

This is because it protects our body against free radicals and oxidative stress. Free radicals being; unstable atoms that damage our cells, increase diseases and cause aging. Green tea contains polyphenols and are an important antioxidant called Epigallocatechin (EGCG). 

EGCG is very powerful. It fights inflammation, prevents heart diseases, aids weight loss as well as carrying many more health benefits. It is a naturally produced plant compound and is known as a catechin. 

It is also thought that drinking teas containing Theanine can help clear your sinuses. It has been said to help your cilia. Cilia being the small fibers in your nose which help clear mucus. 

Sources of L-Theanine

The most natural way to include Theanine in your daily diet is through drinking tea. Both black and green tea contain Theanine. Within a 200ml cup of tea, black tea will contain a higher level than green tea. 

You should follow daily caffeine guidelines for how much you should consume within a day. As for taste, we all know how we like our tea made, and it often differs from person to person. However it is worth noting, that how you like your tea brewed, could effect the amount of Theanine you get in the tea that you drink. 

Theanine is also found within a mushroom known as the Boletus Badius mushroom. However, it isn’t known how much you would need to consume for it to have a beneficial impact. 


Getting L-theanine from your diet can be tricky if you’re not a tea drinker, or skilled in growing mushrooms. Therefore you can buy products such as a L-theanine powder or capsules, as well as various relaxing and calming products that contain it within them – such as nootropics

As with any supplementation, you should always contact your healthcare provider beforehand so that you know it is suitable to take. Especially if you are taking any prescribed medication.

When Is It Best To Take L-Theanine?

The answer to this question depends on what your reason is for taking Theanine. You might be seeking help to become more alert and focused. You might be needing help with feeling less anxious or stressed, or perhaps you need support with improving your sleep. 

We know that caffeine by itself can give us a ‘kick’ that we often need in the morning to help our focus and promote alertness. Therefore, consuming L-theanine combined with caffeine in the morning would be ideal to support cognitive function, and reduce mental fatigue. 

To promote better sleep, a product that includes Theanine as a relaxant would be better taken towards the end of the day. This would help to calm our minds, reduce anxiety and stress. 

Side Effects Of Theanine

With any supplement taking, it is always advised that you follow the recommended dosage and to follow any advisory information that is recommended. Particularly, if you are pregnant or breastfeeding, you must consult your doctor. 

There are no official or confirmed side effects of taking L-theanine. Drinking tea is a safe practice which many of us do and can offer various benefits, as discussed. 

Tea contains caffeine. If you don’t follow the daily guidelines for caffeine intake, which is said to be a maximum of 400mg, then you may find that you could experience side effects. 

Some of the side effects of consuming too much caffeine could be;

  • Irritability
  • Upset stomach
  • Nausea
  • Headache
  • Palpitations 

In Summary

L-theanine is natural occurring amino acid that comes from plant sources such as mushrooms and tea leaves. We now know it has benefits for both your physical and mental health.

In moderation it can help your attention and focus, as well as your ability to relax and sleep. 

Phillippa Quigley headshot

This article was written by: Phillippa Quigley – SOMA Analytics Nutritionist and Holistic Health Coach

Phillippa is the owner and founder of Health and Soul and coaches and supports clients in the field of women’s health, nutrition, stress management, lifestyle, mindset, weight loss and general fitness.

She has a young family, loves the outdoors and has a wide range of hobbies that help her manage her own mental and physical health.