L-Theanine: Health Benefits and Cognitive Function

Ever wonder why a cup of tea is offered during stressful situations? Or why it seems to help us to wind down at night? It’s because tea contains the L-theanine compound. It is found especially in green tea and it can help our body to relax and calm down. 

What is L-Theanine?

L-theanine is an amino acid that is actually not essential for humans although it is known to provide certain health benefits. This amino acid was first found in tea by Japanese scientists in the mid-1900s. Because L-theanine is not essential for our bodily functions, the human body does not synthesize it and we don’t require it in our diets. 

L-theanine mechanism of action

L-theanine’s main mechanism of action is to increase the levels of inhibitory neurotransmitters and block the production of excitatory neurotransmitters. 

Because L-theanine is a glutamic acid analog, it is very similar to the neurotransmitter glutamate. This chemical resemblance means it is able to bind directly to postsynaptic receptors, inhibiting the binding of glutamate. It also binds to the glutamate transporter to prevent the reuptake of glutamate. 

This process results in an increased level of brain inhibitory transmitter GABA and increases dopamine levels. Anti-stress effects are felt due to the inhibition of excitatory neurotransmitters. 

Where is L-Theanine naturally found?

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The most common source of L-theanine is green tea. In fact, L-theanine makes up about 50% of the total amino acids in green tea. It is said that up to 3.1% of the dry weight of green tea is from this amino acid. 

However, L-theanine content varies according to specific types of green tea. Younger green tea plants also tend to have a higher amount of this amino acid. 

Because L-theanine is highly water-soluble, nearly all of it dissolves in water when tea is prepared. It is also believed that this amino acid is responsible for the slight savory umami flavor that is very unique to green tea. 

L-theanine foods

L-theanine can also be found in:

  • Black and white tea leaves but at a lower content than green tea leaves. 
  • Xerocomus badius, a brown, edible, porous mushroom species which is also known as bay bolete. Bay bolete can be found in Europe and North America. 
  • C. japonica and C. sasanqua, small shrubs that are sometimes used to make tea. 

L-Theanine benefits 

While L-theanine is not an essential amino acid that our body needs, it offers tons of great benefits. 

Stress and anxiety relief

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L-theanine in tea is anxiolytic. It helps to reduce anxiety by promoting relaxation and stress without sedative effects. A hot cup of tea can help you keep calm while still being attentive. 

Studies show that L-theanine can significantly reduce stress and anxiety in people who are experiencing stressful situations. It can also be helpful with anxiety for people who are living with schizophrenia or schizoaffective disorder

Increases cognitive function

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A 2016 study found that L-theanine can improve brain function. It helps with attention, reaction time, memory, and learning. 

Hormones like cortisol and corticosterone are produced by our bodies when we are under stress. These hormones can inhibit brain activity, affect memory formation and learning. L-theanine counters this by lowering stress hormone levels and fostering a sense of calm. 

L-theanine is sometimes used with caffeine to enhance alertness, focus, and cognitive skills. It is said that the combination of L-theanine and caffeine can improve one’s ability to process visual information and number skills. 

In a study investigating this combination effect, young adults who were given 97mg of L-theanine and 40mg of caffeine had significantly improved accuracy during task switching. They also reported increase alertness and reduce tiredness. The researchers concluded that the combination of L-theanine and caffeine can help to increase focused attention for demanding cognitive tasks. 

Improves sleep

L-theanine helps people to fall asleep quicker during bedtime because it fosters relaxation and calmness. It also improves sleep quality as it lowers stress and anxiety levels. This is important as deep sleep itself has many health benefits. 

A 2018 study in which participants who were struggling with a generalized anxiety disorder reported better sleep quality after taking 450 to 900mg of L-theanine every day for 8 weeks

Increases immunity

L-theanine can also boost the immune system and has anti-inflammatory properties that help the body in fighting off illnesses. 

Research shows that L-theanine can help with upper respiratory tract infections and in preventing the flu. Studies also show that it can help reduce inflammation in the intestinal tract although more research is needed in this area. 

Anti-tumor effects

Studies have suggested that people who drink tea regularly have a lower risk of cancer. In fact, another study conducted in China found that women who drank green tea had 32% lesser chances of developing pancreatic cancer compared to no tea drinkers. 

It is also said that L-theanine is able to enhance the anti-tumor effect of certain chemotherapy drugs. While more studies are needed, this promising finding suggests that L-theanine will be able to improve chemotherapy’s effectiveness to fight cancer. 

Blood pressure management

A 2012 study found that L-theanine was effective in reducing increased blood pressure due to having to complete specific mental tasks. 

High BP is known to cause health issues like heart attack and strokes. L-theanine helps reduce high blood pressure during stressful situations by reducing stress. Lowering stress and increasing relaxation can decrease heart rate and thus, lower blood pressure. 

Helps with relaxation

There is evidence that suggests that L-theanine in green and black tea can help people relax by reducing their resting heart rate. This is why in some cultures a cup of tea is often offered during stressful situations. 

Weight loss

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L-theanine in green tea creates a savory ‘umami’ flavor that can help reduce appetite. As such, having some green tea instead of a snack can result in weight loss.  

Additionally, the anti-anxiety and sleep-promoting properties of L-theanine can also help in weight management. Getting proper sleep and being well-rested instead of stressed is important when it comes to healthy eating and avoiding weight gain. 

L-Theanine and sleep

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As mentioned above, L-theanine can be a great help for those who are suffering from sleep disorders such as insomnia. Here’s how L-theanine promotes relaxation and sleep:

  • L-theanine boosts calming brain chemicals such as GABA, serotonin, and dopamine. These neurotransmitters regulate our mood, emotions, appetite, energy, alertness as well as sleep. Increased levels of these chemicals in our brains help us to relax and sleep. 
  • L-theanine reduces ‘excitatory’ brain chemicals and chemicals that are linked to stress and anxiety. This results in calm and relaxation. 
  • L-theanine enhances alpha brain waves which are related to ‘wakeful relaxation’ and is present during REM sleep

Because L-theanine is generally safe, and supplementation does not cause drowsiness, dependence, or lead to adverse side effects, it is often used as a natural sleep supplement to improve sleep quality and promote relaxation

How long does L-theanine take to work?

Ingestion of L-theanine doses between 50 to 200mg can usually be felt within 30 to 40 minutes of consumption. As such, taking L-theanine supplements about an hour before bedtime will help you to wind down and relax as you prepare to go to bed. 

How long does L-theanine stay in your system?

The calming effects of a 50 to 200 mg dose of L-theanine can last 8 to 10 hours after consumption. This is perfect for a solid night’s sleep. 

Is L-Theanine safe? 

The Food and Drug Administration classifies L-theanine as ‘generally recognized as safe’. This means that L-theanine is for the most part a safe supplement or additive when it is used according to the suggested dose on labels and packaging. 

L-Theanine side effects and risks

While L-theanine is usually well tolerated by healthy adults and the side effects are very minimal, the following groups of people should check with their doctor before using supplements that contain L-theanine:

  • Women who are pregnant or breastfeeding
  • Young children
  • People who have low blood pressure

Besides this, another point to note is that both green and black tea contain caffeine. Consuming large amounts of tea can result in nausea, stomach upset, and irritability due to over-caffeinating. 

L-Theanine interactions

Although side effects are few, L-theanine may interact with certain medications and supplements. Effects of the interactions include increased or decreased sleepiness, and reducing the effectiveness of medication and supplements that are being consumed. 

Do check with your doctor before taking L-theanine if you are on any of these medications or supplements: 

  • High blood pressure medications
  • High blood pressure supplements
  • Supplements that contain caffeine
  • Stimulants, like those that are used to treat ADHD. 

L-Theanine dosage

While it is unlikely to overdose on this supplement, it is recommended that users begin with the smallest suggested dose. You can slowly increase the dose as required.

For sleep and stress, 50 mg to 400 mg is recommended. This supplement is often available in 200mg tablets. 


L-theanine is an amino acid that offers numerous health benefits, including relaxation, stress relief, and improved sleep quality. If you are having issues sleeping, Rilax is a natural, safe and effective sleep supplement that contains L-theanine, giving your body the healthy and restorative sleep that it needs. 

*Note: Rilax sleep supplement results may vary from individual to individual.

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