L-Theanine Benefits, Usage, Dosage, Side Effects, and More



What is L-Theanine?

L-Theanine is a non-protein amino acid and it’s the main component of Green/Black tea, providing tea’s unique taste and aroma. L-theanine has many scientific research studies on its mechanism of action as a relaxing agent, increasing brain serotonin, dopamine, and GABA levels. While caffeine has been known to contribute to the benefits of tea, L-Theanine benefits have become more significant recently.Green or Black tea is made from the leaves of Camellia sinensis plant ; the only difference between Green and Black tea is the fermentation process of the leaves to produce the Black tea, while Green tea is unfermented. L-Theanine has other scientific names such as Suntheanine, γ–glutamylethylamide, and γ-ethylamino-l-glutamic acid.

L-Theanine Health Benefits

Clinical experimental trials have shown significant health benefits of L-Theanine:
  • Lipid-lowering properties by decreasing hepatic-tumor-induced hyperlipidemia and inhibiting Low-Density Lipoprotein (LDL) which contributes to atherosclerosis.
  • Similarly to lipid-lowering, L-Theanine has a proven effect in decreasing blood pressure significantly at high doses of 2000 mg, which counteracts the caffeine-induced increase in blood pressure.
  • Immunomodulatory functions of L-Theanine are noticed due to enhanced immune T-cells proliferation which is one of the first lines of defense against infections, allergic reactions, and pathogenic bacteria.
  • L-Theanine ability to increase Dopamine and Serotonin in the nerve cells contributes to inducing relaxation, preventing anxiety, and decreasing cortisol levels.
L-Theanine mechanism of action on the brain is still not totally observed, L-Theanine has a similar structure to the Glutamate neurotransmitter that increases L-Theanine affinity to Glutamate receptors in the central nervous system and acts as an antagonist which contributes to the neuroprotective effect of L-Theanine.
l Theanine benfits
Behavioral and cognitive abilities are based on neurotransmitters such as dopamine, serotonin and acetylcholine, since dopamine and serotonin are shown to enhance cognitive functions such as memory, learning, and attention. L-Theanine possible effects are due to boosting the dopamine and serotonin levels in the central nervous system, which improves memory and learning abilities. Clinical studies aimed to observe the combination effect of both L-Theanine and Caffeine on cognitive abilities concluded that Caffeine combined with L-Theanine improved attention switching-task performance, accuracy and speed in addition to reduced distraction probability. Alpha waves are a type of waves produced in the brain naturally during relaxed mood; 50 mg up to 200 mg L-Theanine was observed to enhance the Alpha waves in the parietal and occipital regions of the brain after 40 minutes of administration. 

Possible Adverse Effects of L-Theanine

Moderate daily intake of L-Theanine is safe, and no side effects were reported in any published study.  High doses on daily basis will lead to:
  • Lowering blood pressure (which may be beneficial to some people).
  • Appetite loss.
  • Diarrhea.>
  • Difficulty in concentration.
  • Headache.
  • Nausea.
  • Extreme high doses (29mg/kg/day) can cause liver toxicity.

Example: if someone is 70 kg or approximately 140 LB that will make up over 2000 mg /day (29mg X 70 kg)

How to Take L Theanine
green tea

Is L-Theanine Safe?

  • Regular/modest intake of L-Theanine through supplements or Green/Black tea on the long term (up to 78 weeks) is safe and no side effects were reported.
  • L-Theanine 250 mg/day for 8 weeks has been found to be safe without any reported side effects.
  • No reported toxicological side effects of L-Theanine in vivo and in vitro studies.

How much L-Theanine should I Take Daily?

The FDA recommends that the maximum daily dose of L-Theanine should not exceed 1200 mg.

Is L-Theanine FDA Approved?

L-Theanine is approved by the FDA as “generally recognized as safe.” 

Recommended L-Theanine Doses

  • 50 to 200 mg/ day for cardiovascular benefits.
  • 250 to 400mg/ day for general psychopathology and sleep disorders.

Best L-Theanine Supplement

Best supplements do not rely on a single ingredient only, although L-Theanine is one of the most potent studied ingredients but when combined with adaptogenic nutrients, it will provide a unique blend for mental performance.

Welltopia’s IQ Adapt features a unique blend of botanicals and nutrients (Caffeine-free)

  • L-Theanine.
  • Phosphatidylserine.
  • Bacopa monnieri.
  • Ashwagandha Root Extract.
  • Rhodiola Rosea Root Extract.
  • Eleuthero Root Extract.


  • Mental and physical performance.
  • Memory, focus and attention improvement.
  • Energy production.
  • Stress resistance strength.

Exploring the Unique Properties of L-Theanine in Tea Consumption

L-Theanine, a unique amino acid found in tea, particularly in green and matcha varieties, plays a crucial role in both the flavor and health benefits of these beverages. In green tea, L-theanine imparts a subtle, savory taste known as umami, enhancing the tea’s depth and complexity. Matcha, with its concentrated form, amplifies this effect, offering a richer, more robust flavor. Beyond taste, L-theanine’s influence extends to its calming effects on the mind.

It promotes relaxation and mental clarity, contrasting with the stimulating effects of caffeine. This makes tea an ideal choice for those seeking a balanced state of alert relaxation, contributing positively to mental health and cognitive function. Regular consumption of L-theanine-rich teas can therefore be a delightful sensory experience with significant health implications.

Comparative Analysis of L-Theanine and Other Amino Acids

L-Theanine, distinct among amino acids, stands out for its specific effects on the brain and body, differing significantly from other amino acids found in foods and supplements. While most amino acids are involved in building proteins and muscle repair, L-theanine uniquely influences neurochemistry, promoting relaxation and mental alertness. This contrasts with amino acids like tryptophan, which is known for its role in serotonin production and sleep regulation.

L-theanine’s ability to increase GABA, dopamine, and serotonin levels in the brain sets it apart, offering stress reduction and cognitive enhancement benefits. This makes L-theanine a unique component in the realm of dietary supplements, specifically targeting mental well-being and cognitive function, unlike other common amino acids.



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