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L-Theanine: Everything You Need To Know

What Is L-Theanine?

L-theanine is an amino acid found in tea leaves (Camellia sinensis) and the Bay bolete mushroom (Xerocomus badius).1 L-theanine is also available in supplement form.

Clinical trials suggest L-theanine has anti anxiety effects and promotes relaxation, sleep, cognitive function (processing and understanding information), and more.23456

Different types of tea have different amounts of L-theanine. One study suggested white and green teas contain more L-theanine than oolong and black.7 Prepared teas were found to have anywhere from 5 to 36 milligrams (mg) of L-theanine per cup.8

The longer tea leaves are steeped, the more L-theanine (and caffeine) is extracted. Maximum levels can take up to 20 minutes or more to develop.7

Read on for more about L-theanine benefits, safety, and more.

Supplement Facts
  • Active ingredient(s): 5-N-ethyl-L-glutamine
  • Alternate name(s): 5-N-ethyl-L-glutamine, γ-glutamylethylamide, Suntheanine, theanine9
  • Legal status: Over-the-counter supplement. Generally recognized as safe (GRAS).10
  • Suggested dose: Varies by condition.
  • Safety considerations: Pregnancy, breastfeeding, chemotherapy;9 potential interactions with medications and other supplements, such as those for blood pressure.11
What Are L-Theanine’s Benefits?

However, it’s important to note that better-designed clinical trials are still needed.


ADHD Symptoms

Researchers have investigated L-theanine for attention deficit hyperactivity disorder (ADHD) symptoms.

Attention issues can have the following causes and/or associations:

  • Lead exposure
  • Brain injury
  • Family stress
  • Thyroid conditions
  • Inflammatory bowel conditions
  • Nutrition issues, including zinc or iron deficiency 12
  • Addressing any underlying issues is worth considering. If you have questions about your child’s symptoms, it’s best to contact their pediatrician.

A study was conducted in male children (8 to 15 years) with ADHD. Compared to a placebo (an inactive substance), L-theanine improved total cognition. Both L-theanine alone and an L-theanine-caffeine combination also reduced mind wandering.13

Caffeine Use in Children

The American Academy of Child and Adolescent Psychiatry (AACAP) advises against caffeine for children under 12 years.14

Some children with ADHD may also have significant issues with sleep. Sleep disturbances can impact both a child’s and family’s well-being. A clinical study suggested L-theanine helped sleep quality in male children 8 to 12 years with ADHD.
Further, higher-quality studies are needed to confirm these results.

Correct Diagnosis of ADHD

Correctly diagnosing ADHD is essential. Some gifted (highly or profoundly intelligent) children may have behaviors that seem like ADHD due to boredom or other issues.15 ADHD, autism spectrum disorder (ASD), and giftedness can also share overlapping characteristics and can be correlated.16 A healthcare provider well-versed in both giftedness and neurodiversity can help. Organizations like the National Association for Gifted Children have additional resources.1718

Another study showed younger males in kindergarten were, as a group, over-diagnosed with ADHD.19 Developmentally normal behavior has been mistaken for a medical issue.20

Ask your child’s healthcare provider about questions or concerns. They may refer you to a healthcare provider that specializes in these areas.


Anxiety affects around 12.5% of adults and 9.4% of children in the United States.2122 Unresolved anxiety can cause further health issues.

Scientists found L-theanine has anxiolytic (anti-anxiety) effects. A systematic review (a collection of research on a single topic) suggested L-theanine reduced anxiety in people under stress.5

Researchers conducted a study in children between 4 and 17 years with Tourette’s syndrome (a nervous system condition causing sudden twitches, movements, and sounds). L-theanine with vitamin B6 reduced tics with anxiety.6 It’s challenging to fully understand L-theanine’s effects in this study alone as it was used in combination.

While there’s promising evidence, conflicting evidence of theanine’s effectiveness for anxiety also exists.2324

Speak with your healthcare provider if you’re experiencing anxiety.


Scientists have suggested caffeine may bolster L-theanine’s impact on cognition (processing and understanding information) and working memory.25

In a study of young adults, L-theanine with caffeine helped with attention.26

However, in other studies of healthy adults, L-theanine alone (no caffeine added) had the following effects:

  • Decreased errors27
  • Increased attention2829
  • Enhanced working memory28
  • Promoted verbal fluency (retrieving information from memory)30
  • Improved executive function2830
  • Increased selective attention (the ability to select and process information while tuning out distractions)29

Theanine has been investigated for its anticancer effects in in vitro (in cells in a laboratory) and in vivo (animal) studies.31

However, clinical trials (research in humans) are needed before recommendations can be made.
In one study, researchers added L-theanine to current medication in people with major depressive disorder. The following symptoms improved:

Depressive symptoms
  • Anxiety
  • Sleep disturbance
  • Cognitive impairments 4

Further, high-quality studies are needed.

Please reach out to your healthcare provider if you’re experiencing depression. Promptly diagnosing and treating this and other mental health issues is important.

Immune Effects

L-theanine impacts the immune system. In a study of professional athletes, L-theanine had effects on different immune system markers.32 It was associated with decreased interleukin-10 (IL-10). Further study is needed.


In people with schizophrenia or schizoaffective disorder, L-theanine was added to regular treatment with beneficial effects.3334

L-theanine supplementation was associated with the following improvements:

Sleep quality

Positive and Negative Syndrome Scale (PANSS) scores (assesses how well treatment is working)
Consult with your healthcare provider before adding supplements to your medication regimen.


Chronic sleep disorders can seriously affect your quality of life. Sleep disorders are linked with or can worsen the following conditions:

  • Anxiety
  • Cardiovascular disease
  • Depression
  • Diabetes 2


In healthy adults, L-theanine reduced sleep latency (the time it takes to fall asleep), sleep disturbance, and the use of sleep medication.30
Some children with ADHD have associated sleep problems, affecting both the child’s and family’s well-being.35 In a clinical study of male children 8 to 12 years with ADHD, L-theanine improved sleep.3

If you or your child has sleep issues, please reach out to your healthcare provider.

It’s essential to evaluate and rule out contributing issues such as:

  • Sleep apnea
  • Restless legs syndrome
  • Insomnia
  • Iron deficiency anemia12
  • Sleep issues can be connected with behavior and mood issues in adults and children.

Your healthcare provider can help you figure out and address the root cause.


Researchers studied theanine for its stress-reducing effects.36 In young adults, L-theanine reduced stress. It also lowered blood pressure in high-stress situations.11

Further study is needed to confirm these results.

What Are L-Theanine’s Downsides?

L-theanine has been mostly well-tolerated in clinical trials. However, adverse effects or interactions are still possible, including the following:

Allergy: People who are allergic or hypersensitivity to any part of L-theanine products should avoid it. Carefully read your product labels. If you’re having a severe allergic reaction to L-theanine, symptoms may include breathing difficulties, itchiness, and rash. Call 911 and seek prompt medical attention if you have a severe allergic reaction or any life-threatening symptoms.

Anxiety medications: Theanine reduced anxiety in a clinical study. Theoretically, it may interact with medications or other supplements used for anxiety.2

Blood pressure medication: Theanine has lowered blood pressure in clinical study. Theoretically, it may interact with medications or other supplements that affect blood pressure.11

Cancer medication: Using L-theanine supplements while undergoing chemotherapy is best done in collaboration with your healthcare provider.319

Pregnancy or breastfeeding: Pregnant or breastfeeding people should likely avoid L-theanine supplements.9 Speak with your healthcare provider or pharmacist for further information.

It is essential to carefully read a supplement ingredients list and nutrition facts panel to know which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss potential interactions with foods, other supplements, and medications.

How Does L-Theanine Work?

Researchers believe L-theanine improves sleep quality via anxiolysis (reducing anxiety), not sedation.2

Scientists believe these effects may be due to theanine’s ability to benefit levels of the following:

  • Glutamate
  • GABA (gamma-aminobutyric acid)
  • Serotonin
  • Dopamine
  • Alpha-wave brain activity11333738

L-theanine also impacted levels of the following when used with antipsychotic medication:

  • Dehydroepiandrosterone (DHEA)
  • DHEA’s sulfate (DHEAS)
  • Cortisol
  • Brain-derived neurotrophic factor (BDNF)39

Researchers think BDNF may help the brain heal itself, which might explain some of theanine’s positive benefits.39


Since its discovery in the 1940s, researchers have investigated L-theanine for ADHD, anxiety, cognition, stress, and more.

While results are promising, more research is needed.

Consider avoiding L-theanine in the following situations:

  • Pregnancy
  • Breastfeeding
  • Chemotherapy

And please do your best to speak with your healthcare provider, registered dietitian nutritionist (RD or RDN), and/or pharmacist about your supplements, prescriptions, and over-the-counter medication.

This way, you can collaboratively come up with a plan that optimizes safety and helps successfully meet your health goals.


Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Chen Z, Wang Z, Yuan H, He N. From tea leaves to factories: a review of research progress in l-theanine biosynthesis and production. J Agric Food Chem. 2021;69(4):1187-1196. doi:10.1021/acs.jafc.0c06694
  2. Rao TP, Ozeki M, Juneja LR. In search of a safe natural sleep aidJ Am Coll Nutr. 2015;34(5):436-447. doi:10.1080/07315724.2014.926153
  3. Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trialAltern Med Rev. 2011;16(4):348-354.
  4. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label studyActa Neuropsychiatr. 2017;29(2):72-79. doi:10.1017/neu.2016.33
  5. Williams JL, Everett JM, D’Cunha NM, et al. The effects of green tea amino acid l-theanine consumption on the ability to manage stress and anxiety levels: a systematic reviewPlant Foods Hum Nutr. 2020;75(1):12-23. doi:10.1007/s11130-019-00771-5
  6. Rizzo R, Prato A, Scerbo M, et al. Use of nutritional supplements based on l-theanine and vitamin B6 in children with Tourette syndrome, with anxiety disorders: A pilot studyNutrients. 2022;14(4):852. doi:10.3390/nu14040852
  7. Boros K, Jedlinszki N, Csupor D. Theanine and caffeine content of infusions prepared from commercial tea samplesPharmacogn Mag. 2016;12(45):75-79. doi:10.4103/0973-1296.176061
  8. Keenan EK, Finnie MD, Jones PS, et al. How much theanine in a cup of tea? Effects of tea type and method of preparationFood Chem. 2011;125(2):588-594. doi:10.1016/j.foodchem.2010.08.071
  9. PubChem. Theanine.
  10. Food and Drug Administration. GRAS Notices.
  11. Yoto A, Motoki M, Murao S, Yokogoshi H. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stressesJ Physiol Anthropol. 2012;31(1):28. doi:10.1186/1880-6805-31-28
  12. Vuong QV, Bowyer MC, Roach PD. L-theanine: properties, synthesis and isolation from teaJ Sci Food Agric. 2011;91(11):1931-1939. doi:10.1002/jsfa.4373
  13. Kahathuduwa CN, Wakefield S, West BD, et al. Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCTSci Rep. 2020;10(1):13072. doi:10.1038/s41598-020-70037-7
  14. The American Academy of Child and Adolescent Psychiatry. Caffeine and children.
  15. François-Sévigny J, Pilon M, Gauthier LA. Differences in parents and teachers’ perceptions of behavior manifested by gifted children with ADHD compared to gifted children without ADHD and non-gifted children with ADHD using the Conners 3 scaleBrain Sci. 2022;12(11):1571. doi:10.3390/brainsci12111571
  16. Antshel KM, Russo N. Autism spectrum disorders and ADHD: Overlapping phenomenology, diagnostic issues, and treatment considerationsCurr Psychiatry Rep. 2019;21(5):34. doi:10.1007/s11920-019-1020-5
  17. National Association for Gifted Children. Resources.
  18. National Association for Gifted Children. NAGC State Affiliates.
  19. Whitely M, Raven M, Timimi S, et al. Attention deficit hyperactivity disorder late birthdate effect common in both high and low prescribing international jurisdictions: a systematic reviewJ Child Psychol Psychiatry. 2019;60(4):380-391. doi:10.1111/jcpp.12991
  20. Layton TJ, Barnett ML, Hicks TR, et al. Attention deficit-hyperactivity disorder and month of school enrollmentN Engl J Med. 2018;379(22):2122-2130. doi:10.1056/NEJMoa1806828
  21. Centers for Disease Control. Data and statistics on children’s mental health.
  22. Centers for Disease Control. Early release of selected estimates based on data from the 2022 National Health Interview Survey.
  23. Sarris J, Byrne GJ, Cribb L, et al. L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trialJ Psychiatr Res. 2019;110:31-37. doi:10.1016/j.jpsychires.2018.12.014
  24. Zhang W, Yan Y, Wu Y, et al. Medicinal herbs for the treatment of anxiety: A systematic review and network meta-analysisPharmacol Res. 2022;179:106204. doi:10.1016/j.phrs.2022.106204
  25. Mancini E, Beglinger C, Drewe J, Zanchi D, Lang UE, Borgwardt S. Green tea effects on cognition, mood and human brain function: A systematic reviewPhytomedicine. 2017;34:26-37. doi:10.1016/j.phymed.2017.07.008
  26. Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertnessNutr Neurosci. 2010;13(6):283-290. doi:10.1179/147683010X12611460764840
  27. Foxe JJ, Morie KP, Laud PJ, et al. Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention taskNeuropharmacology. 2012;62(7):2320-2327. doi:10.1016/j.neuropharm.2012.01.020
  28. Baba Y, Inagaki S, Nakagawa S, et al. Effects of l-theanine on cognitive function in middle-aged and older subjects: a randomized placebo-controlled StudyJ Med Food. 2021;24(4):333-341. doi:10.1089/jmf.2020.4803
  29. Dassanayake TL, Kahathuduwa CN, Weerasinghe VS. L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover studyNutr Neurosci. 2022;25(4):698-708. doi:10.1080/1028415X.2020.1804098
  30. Hidese S, Ogawa S, Ota M, et al. Effects of l-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trialNutrients. 2019;11(10):2362. doi:10.3390/nu11102362
  31. Shojaei-Zarghani S, Rafraf M, Yari-Khosroushahi A. Theanine and cancer: a systematic review of the literaturePhytother Res. 2021;35(9):4782-4794. doi:10.1002/ptr.7110
  32. Juszkiewicz A, Glapa A, Basta P, et al. The effect of L-theanine supplementation on the immune system of athletes exposed to strenuous physical exerciseJ Int Soc Sports Nutr. 2019;16(1):7. doi:10.1186/s12970-019-0274-y
  33. Ota M, Wakabayashi C, Sato N, et al. Effect of L-theanine on glutamatergic function in patients with schizophreniaActa Neuropsychiatr. 2015;27(5):291-296. doi:10.1017/neu.2015.22
  34. Ritsner MS, Miodownik C, Ratner Y, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center studyJ Clin Psychiatry. 2011;72(1):34-42. doi:10.4088/JCP.09m05324gre
  35. Anand S, Tong H, Besag FMC, et al. Safety, tolerability and efficacy of drugs for treating behavioural insomnia in children with attention-deficit/hyperactivity disorder: A systematic review with methodological quality assessment. Paediatr Drugs. 2017;19(3):235-250. doi:10.1007/s40272-017-0224-6
  36. White DJ, De Klerk S, Woods W, et al. Anti-stress, behavioural and magnetoencephalography effects of an l-theanine-based nutrient drink: a randomised, double-blind, placebo-controlled, crossover trialNutrients. 2016; 8(1):53. doi: 10.3390/nu8010053.
  37. Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental stateAsia Pac J Clin Nutr. 2008;17 Suppl 1:167-168.
  38. Anas Sohail A, Ortiz F, Varghese T, et al. The cognitive-enhancing outcomes of caffeine and l-theanine: a systematic reviewCureus. 2021;13(12):e20828. doi:10.7759/cureus.20828
  39. Miodownik C, Maayan R, Ratner Y, et al. Serum levels of brain-derived neurotrophic factor and cortisol to sulfate of dehydroepiandrosterone molar ratio associated with clinical response to L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patientsClin Neuropharmacol. 2011;34(4):155-160. doi:10.1097/WNF.0b013e318220d8c6
  40. National Institutes of Health. Dietary supplement label database.


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