L-Theanine Benefits, Side Effects, Dosage And Stacking

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L-theanine is found in black and green teas

What Is L-Theanine?

Supplements containing L-Theanine have become quite popular in the recent past primarily because a number of recent researches 1 have revealed that this compound helps with keeping stress levels at bay 2, promoting relaxation, and fighting mental disorders, not to mention a wide array of health benefits attributed to it.

By definition, L-Theanine is a potent amino acid that is specifically present in black and green tea and other types of teas from the Camellia Sinensi family 3. It is largely viewed as a relaxing amino acid, for it is capable of promoting relaxation 4 by enhancing the release of the alpha-brain waves into the human brain 5.

L-Theanine Dosage

There is no specified dosage of L-Theanine 6 that has been suggested so far, thanks to the fact that the appropriate dosage depends on various factors like health and age of the user. When L-Theanine supplementation is administered orally7, it is absorbed in the bloodstream quite fast, thus ensuring that the effects are felt within minutes after ingestion8. Accordingly, it is recommended that it is taken in standard dosages of about 50mg to 200mg twice a day, particularly when it is being taken alone without of any other supplements.

While using L-Theanine supplements, WebMed recommends 9 users to follow the prescription outlined on the product label. For best possible results, L-Theanine can be administered with caffeine, where the standard dosage should be 200 mg of this amino acid and 100 mg of caffeine 10.

What Are The Top Benefits?

Many people take L-Theanine for its anxiety-reducing effects. Reducing anxiety is the primary benefit of L-Theanine, but L-Theanine has many other benefits which people aren’t necessarily aware of.

It has powerful antioxidants effects

Due to its powerful antioxidants effects, L-Theanine offers multiple health benefits, such as boosting a healthy cardiovascular system. More specifically, this amino acid counters the oxidative stress 11 that may hamper proper blood circulation. Other studies 12 have also indicated that ingestion of L-Theanine can help lower blood pressure, and reduce the risk of cardiovascular diseases.

Boosts alertness and cognitive performance

Research after research has demonstrated that L-Theanine can play a vital role in boosting alertness and cognitive performance. For instance, a clinical study 13 involving some healthy volunteers found that participants who took caffeine with L-Theanine had an improved alertness as opposed to their counterparts who took caffeine without L-Theanine.

Improves sleep quality

Numerous studies show that L-Theanine can help improve sleep quality. A clinical observation 14 that involved 98 boys linked L-Theanine with a good night sleep. In this study, one group of the boys was given two 100mg tablets of chewable L-Theanine twice a day. The rest of them were given placebo pills. After the 6th week, the group that consumed L-Theanine noted they experienced more restful sleep than their counterparts who took placebo pills. In another study 15, L-Theanine was proved to help improve the symptoms of schizophrenia by improving sleep quality.

Improves Focus

L-Theanine boosts the activity of the alpha brain waves, consequently bringing a focused and relaxed feeling. The nootropic nature of this compound makes it effective for learning, focused-studying, and creative pursuits. It is also suitable for tasks that require focused attention 16 because it helps enhance attention and improve reaction time response. In a study17 involving young adults, those who took about 97-40 mg of L-Theanine and caffeine experienced increased focus as opposed to the young adults who never took L-Theanine.

Helps fight cancer and tumor growth

There is evidence that a special type of L-Theanine present in Bay Bolete mushrooms 18can be combined with some specific chemotherapy drugs to speed up their activity thus making these drugs quite effective. These findings have prompted health researchers to indicate that this amino acid can be used as an effective cancer-fighting agent. Previous studies 19 also indicated that L-Theanine can help reduce tumor growth once combined with a regimen of doxorubicin.

In another finding20 that sought to establish the effect of L-Theanine on leukemia and lung cancer, where some cells were treated with L-Theanine, cells that were left untreated did not show optimum inhibition while those that were treated did. This was indicative of this amino acid’s ability to inhibit leukemia and lung cancer cells.

Powerful nerve protector

L-Theanine helps prevent brain cells damage by countering the overstimulation of brain cells whenever oxygen levels are remarkably low. A Clinical research21 that was done in 2015, and which aimed at proving the protection ability of L-Theanine on countering nerve damage, concluded that this amino acid is a powerful nerve protector. The study, which basically entailed the use of rats, found that the rats that were treated with L-Theanine showed lesser nerve damage than their counterparts that were not treated using the amino acid. Researchers at the Boston University further found out that L-Theanine can be used as a powerful therapeutic agent for treating Parkinson’s disease-related symptoms22 as well as other psychiatric conditions.

Improved Immunity

There is substantial evidence 23 that L-Theanine can help enhance the immune system, and protect the body against virus infections. It is vital for the proper functioning of the cardiovascular system, in addition to triggering the body to release more GABA, thus reducing anxiety levels. L-Theanine is also proved to aid in decreasing the risk of respiratory tract infections 24.

What Are The Potential Side Effects?

The side effects of L-Theanine are not well-documented. It is believed to be safe when taken orally, in form of beverages or food. Moreover, side effects have not been reported when one takes the proper dosage of L-Theanine. Nevertheless, L-Theanine could have similar side effects to those of green tea 25, specifically because of a compound known as polyphenol EGCG. This compound is known to reduce the efficiency of some chemotherapy drugs. That is why persons taking any chemotherapy drugs need to consult with their doctors prior to taking any L-Theanine drugs. This is imperative for preventing any negative effects brought about by the combination of L-Theanine and chemotherapy drugs.

Moreover, long-term consumption of L-Theanine can have similar effects to those linked with consumption of caffeine— behavioral changes in humans 26
. In this regard, over-consumption of L-Theanine should be restricted to the proper dosage, whether taken as a drug, a supplement, or in the form of tea.

Supplementing Your Diet With L-Theanine

There are several ways that you can take L-Theanine and still reap the multiple health benefits of this amino acid:

In the form of food

You can take L-Theanine in form of food, either on a full stomach or on an empty stomach. It is recommended to take the supplement when still on an empty stomach since it is more likely to produce stronger effects than when your stomach is full.

In the form of a tea

When taken in form of tea or any other beverage, L-Theanine becomes more effective because it is directly absorbed into the bloodstream almost instantly. Again, it can remain in the bloodstream for several hours, thus enabling the body to get as many benefits of this amino acid as possible.

In the form of a capsule

There are many types of L-Theanine capsules. The best part about taking L-Theanine as a capsule is that it allows you to take proper dosage. Nonetheless, precaution has to be taken when purchasing L-Theanine capsules since not all of them contain genuine L-Theanine.

With health-promoting substances

Combining L-Theanine with health-promoting substances helps you get the most benefits possible from the supplements you combine it with.  Some of the most common health-promoting substances that can be combined with L-Theanine includes Quercetin, Green Tea Extracts, and Taurine.


L-Theanine can be more effective when stacked with various herbs/ supplements, including:

Huperzine –A

This natural nootropic is sourced from Chinese club moss plant, which is prevalent in China. Huperzine-A is regarded as a medicinal plant that is capable of countering Alzheimer’s disease27 and further enhance memory. Accordingly, when stacked with L-Theanine, it can boost the latter’s ability to counter Alzheimer disease, and further keep the brain well balanced. Additionally, stacking the two makes them highly effective in curbing mental illnesses and boosting the user’s overall mental health.

Artichoke Extract

An extract derived from the dry leaves of artichoke tree can be a powerful antioxidant agent, based on the fact that artichoke extract boasts strong antioxidant properties 28. When combined with another powerful antioxidant like L-Theanine, this extract can help speed up the antioxidant activity of L-Theanine, thus making it even more powerful.


Clinical tests 29 have shown that caffeine and L-Theanine can boost cognitive response and mood when paired together. Since caffeine is potent, especially in high quantities, adding L-Theanine to caffeine can significantly reduce its effectiveness. The right dosage to follow when stacking L-Theanine with caffeine is a ratio of 1:4. That means 400mg of the amino acid should be paired with 100mg of caffeine.

Lion’s Mane

This edible mushroom is also stocked in gourmet food stores in a supplement version, and it can easily be stacked with L-Theanine to counter depression and anxiety. Numerous studies have been conducted in a bid to discover the mushroom’s full potential and noted that it can significantly boost cognitive functionality.

L-Theanine Alternatives

There are several herbs and supplements that have similar effects as L-Theanine, and can be used as alternatives to this amino acid:


Just like L-Theanine, Ginger boasts of extremely powerful antioxidants effects 30 thus making a suitable alternative to L-Theanine supplements. Due to its powerful oxidation effects, ginger is suitable for healing nerve damage and reducing inflammation. Antioxidants can be used for treating acute central nervous system injury, through antioxidants therapy 31. This makes ginger an effective antioxidant agent for fighting nerve damage.


This herb has a thing in common with L-Theanine. The two have been associated with an improved immune system. While Echinacea has several medicinal uses 32, it is most noted for the vital role it plays when it comes to boosting the immune system. It can easily stimulate the immune system 33 to boost immune cell response.


Garlic and L-Theanine have the ability to fight cancer and lower the growth of tumors. A study 34that was carried out to establish garlic cancer-fighting ability established that garlic can actually play a role in fighting against cancer and tumor growth.


Like L-Theanine, peppermint also helps improve the quality of sleep. No wonder it is widely used in aromatherapy for sleep improvement 35. Like L-Theanine that is known to aid with enhancing cognitive performance 36, the aromas of peppermint when combined with other essential oils can help modulate cognitive performance, and also improve work performance.

L-Theanine Tea

Taking L-Theanine tea can be as effective as taking any L-Theanine supplements. However, longer brewing times are often discouraged when making this medicinal tea, because it can result in high quantities of amino acids. Dosage should also be taken into consideration when brewing L-Theanine tea. This is how to prepare L-Theanine tea:

  1. Steep tea for 30 minutes at 80 degrees Celsius
  2. Using water to tea ratio, mix 20ml of tea with 1 gram of L-Theanine.

Final Thoughts

L-Theanine is an important amino acid that can have multiple health benefits when used effectively. The fact that it is a natural amino acid means that it can provide a natural remedy for various health problems. Better still, it can be combined with other supplements to make it even more powerful and effective. By boosting the immune system, protecting the brain against neural damage, enhancing memory, and cognitive performance to fighting cancer and stopping tumor growth, this amino acid is worth consideration. Its usage is highly recommended due to its safe nature and lack of any clinically proven adverse effects. However, usage should be restricted to the prescribed dosage. Additionally, you still need to consider any possible side effects of L-Theanine while using it. If you think it isn’t suitable for you, then you can try a variety of L-Theanine alternatives or stack it with various herbs/supplements of your choice.

Scientific & Reference Citations

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