L-theanine for Anxiety, Sleep, and Focus—Benefits, Uses, and Side Effects

Posted by Medical Board on June 22, 2022 in Uncategorized Last updated on June 22, 2022

Based on recent National Health Interview Survey results, over 11% of all adults currently experience at least some form of persistent worry, nervousness, or anxiety in the United States.[2] According to clinical studies more than 25% of Americans will suffer from at least one anxiety disorder in their lifetime.[7] 

Amino Acids and Anxiety—The Biochemical Connection

Our understanding of fear, anxiety, and neurocircuitry, and how the body and brain react to stress has increased greatly over the past three decades.[7]

Within the field of mental health and psychiatry there has been considerable study over the role that amino-acid neurochemical systems play in stress and anxiety.  GABA (gamma amino acid butyric gamma acid) is an inhibitory neurotransmitter in the central nervous system that acts as a “brake” during stressful times.

GABA deficits can be linked to anxiety and other neuropsychiatric conditions that involve stress and mental health.[7]

We now know there is clinical evidence that dietary intake of branch chain amino acids impacts the chances of developing depression and anxiety.[3]


L-theanine (N-ethyl-L-glutamine) is an amino acid found in green tea that acts as a relaxing agent on the mind and body.  L-theanine is thought to reduce anxiety, promote focus and cognition, and improve sleep quality.  The body does not naturally produce L-theanine nor is it an essential element.

Benefits of L-theanine Supplementation

Increased Mental Focus—Either taken alone (100 mg) or combined with caffeine, L-theanine helps increase focus and cognition.  It closely mimics the natural amino acid GABA and its ability to penetrate the blood brain barrier to raise serotonin levels.

Better Quality Sleep—L-theanine helps induce sleepiness and promotes deeper, more restorative sleep by balancing chemicals within the brain.  These include elevating serotonin which gets converted to melatonin, causing drowsiness.  This is derived from the amino acid tryptophan.

Deep Relaxation and Reduced Anxiety—Helps promote relaxation by possibly lowering the resting heart rate.  L-theanine also acts on neurotransmitters to boost certain “feel good” chemicals that induce calm in the brain.  In studies, 200 mg of L-theanine helped increase brain alpha-waves while decreasing beta-waves associated with stress.

How Does L-theanine Work?—Receptors and Neurotransmitters

Neurochemical animal studies suggest that L-theanine works to increase serotonin levels in the brain.  Serotonin helps modulate mood, cognition, reward, learning, and memory.  As a neurotransmitter, serotonin sends chemical messages between nerve cells.

L-theanine is also thought to elevate dopamine, the feel-good neurotransmitter, and GABA (gamma aminobutyric acid) the main inhibitory neurotransmitter in the human nervous system.  Research also suggests that L-theanine binds with specific glutamate receptors involved in fast excitatory transmission and learning and memory.[1]

The L-theanine Mechanism

L-theanine (γ-glutamylethylamide) is a non-protein amino acid that is found in green tea (Camellia sinensis).  The structure of L-theanine closely mimics that of L-glutamic acid that interacts with glutamate receptors to send messages to the brain. 

In short, natural, non pharmaceutical L-theanine could help prevent stress induced mental health issues including anxiety.[4]

Where Does L-theanine Come From?

L-theanine is found in green tea, black tea, and some mushrooms.  Synthesized through the tea roots, L-theanine is mostly bioavailable in the leaves.  Traditionally, the extraction of non-proteinogenic amino acid derived from the tea plant (Camellia Sinensis) is naturally limited by environmental conditions.  This is because there are coproduced undesirable ingredients that negatively affect the formula for healthy L-theanine ingestion.[5] Rather than attempt to separate specific chemicals from L-theanine, microbial engineering processes using enzymatic catalysis and fermentation can be applied. These tools, together with other agricultural strategies ensure higher yields of L-theanine for commercial use.[5]

Tests and Trials for L-theanine

In clinical trials L-theanine was tested against a placebo where salivary cortisol, EEG readings, blood pressure, and heart rate were then evaluated.[6]

In randomized controlled trials, supplementing with just 200-400 mg of L-theanine per day was found to reduce stress and anxiety in participants placed under stressful conditions.[9]

In another university study it was found that 200 mg of L-theanine, along with small amounts of chamomile, PS, and alpha GPC reduced stress significantly after one hour.  In addition, the cortisol response was greatly reduced three hours post dosage.[8]

What Form Does L-theanine Come In?

L-theanine as a nutrition supplement is available in liquid, capsule, and powder form.  Although green tea contains the amino acid, L-theanine, a single cup yields less than 40 mg per serving.


The optimal adult dosage of L-theanine for stress and anxiety is between 100 and 400 mg.   

Side Effects

There are no known side effects from L-theanine supplementation, however pregnant or breastfeeding mothers should not take the amino acid. 

L-theanine may also interact with certain medications including:

  • Prescription medication taken for high blood pressure
  • Natural supplements that lower blood pressure
  • ADHD medications that stimulate the nervous system
  • Some natural supplements that contain high levels of caffeine

While many Americans will continue to cope with anxiety, stress, and insomnia in their lifetime, L-theanine supplementation provides a low-cost natural option for those who suffer.


1C;, N. P. J. L. K. G. M. O. (n.d.). The neuropharmacology of L-theanine(n-ethyl-L-glutamine): A possible neuroprotective and cognitive enhancing agent. Journal of herbal pharmacotherapy. Retrieved March 18, 2022, from https://pubmed.ncbi.nlm.nih.gov/17182482/ 

2Centers for Disease Control and Prevention. (2022, February 1). FastStats – Mental Health. Centers for Disease Control and Prevention. Retrieved March 18, 2022, from https://www.cdc.gov/nchs/fastats/mental-health.htm 

3Dietary intake of branched-chain … – pubag.nal.usda.gov. (n.d.). Retrieved March 18, 2022, from https://pubag.nal.usda.gov/catalog/7258088 

4Hidese, S., Ogawa, S., Ota, M., Ishida, I., Yasukawa, Z., Ozeki, M., & Kunugi, H. (2019, October 3). Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: A randomized controlled trial. Nutrients. Retrieved March 18, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836118/ 

5Liu, S.-H., Li, J., Huang, J.-A., Liu, Z.-H., & Xiong, L.-G. (1970, January 1). New advances in genetic engineering for L-theanine biosynthesis. New advances in genetic engineering for l-theanine biosynthesis. Retrieved March 18, 2022, from https://pubag.nal.usda.gov/catalog/7415486 

6A study to investigate the efficacy of AlphaWave® L-theanine on stress – full text view. Full Text View – ClinicalTrials.gov. (n.d.). Retrieved March 18, 2022, from https://clinicaltrials.gov/ct2/show/NCT04706494 

7U.S. National Library of Medicine. (n.d.). Home – PMC – NCBI. National Center for Biotechnology Information. Retrieved March 18, 2022, from https://www.ncbi.nlm.nih.gov/pmc/ 

8White, D. J., de Klerk, S., Woods, W., Gondalia, S., Noonan, C., & Scholey, A. B. (2016, January 19). Anti-stress, behavioural and magnetoencephalography effects of an L-theanine-based nutrient drink: A randomised, double-blind, placebo-controlled, crossover trial. Nutrients. Retrieved March 18, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728665/ 

9Williams JL;Everett JM;D’Cunha NM;Sergi D;Georgousopoulou EN;Keegan RJ;McKune AJ;Mellor DD;Anstice N;Naumovski N; (n.d.). The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: A systematic review. Plant foods for human nutrition (Dordrecht, Netherlands). Retrieved March 18, 2022, from https://pubmed.ncbi.nlm.nih.gov/31758301/ 

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