L-Theanine And Sleep

Table of Contents

green tea with l-theanine

On their quest for better sleep, many people turn to enjoying a cup of hot tea or taking a supplement as part of their nightly regimen. Compounds like L-Theanine can be found in tea and supplements, which many people find beneficial for catching more z’s. Understanding the association between L-Theanine and sleep can help you decide whether it makes sense for you to add it to your bedtime routine.

Note: The content on Sleepopolis is meant to be informative in nature, but it shouldn’t be taken as medical advice, and it shouldn’t take the place of medical advice and supervision from a trained professional. If you feel you may be suffering from any sleep disorder or medical condition, please see your healthcare provider immediately.

What is L-Theanine? 

L-Theanine is an amino acid. Amino acids are compounds your body uses for processes like building proteins and enzymes, producing neurotransmitters and hormones, supporting immune function, and providing energy.[1] They are naturally found in foods. 

Of the 20 amino acids, 9 are essential, meaning that your body cannot make them itself and must get them from the food you eat. The remaining 11 amino acids are nonessential, indicating that your body can produce them from cells and other amino acids

L-Theanine is considered a nonessential amino acid. It’s not found in many commonly consumed foods except certain teas — it’s thought to be responsible for their umami flavor. L-Theanine can also be found in supplemental form, which many people use because of its low prevalence in food sources.

How Does L-Theanine Work? 

L-Theanine isn’t used to make proteins or enzymes in your body but to influence nerve impulses in your brain and trigger the release of neurotransmitters. One of these is called GABA — or gamma-aminobutyric acid — which is involved in mood regulation and can have a calming effect.[2]

L-Theanine And Sleep

Because of its involvement in the release of GABA, L-Theanine is sometimes used as a compound to promote better sleep. It helps reduce feelings of anxiety and stress that can otherwise prevent you from falling asleep and staying asleep easily. In fact, researchers say that L-Theanine doesn’t have a sedative effect as much as it helps improve sleep by reducing anxiety.[3] Here’s what research has shown regarding the relationship between L-Theanine and sleep: 

  • A 2022 randomized double-blind, placebo-controlled, cross-over study investigated the effects of a supplement containing 150mg alpha-s1-casein tryptic hydrolysate and 50mg L-theanine versus placebo on poor sleep patterns among working adults. After 4 weeks of daily supplementation, the authors found that those who took the L-theanine-containing supplement experienced improved sleep latency and duration, increasing their total sleeping time by 45 minutes compared to the placebo group.[4]
  • A 2019 animal study found that a mixture of L-Theanine and GABA, the neurotransmitter it activates, positively affected the ability to fall asleep and stay asleep. Researchers noted that the supplementation increased rapid eye movement (REM) sleep, which is the phase of sleep associated with dreaming and memory consolidation, and non-REM sleep, which are phases of deep sleep.[5]
  • In a 2019 randomized controlled trial, 30 healthy adults were given 200 mg/day of L-Theanine or placebo tablets for four weeks. Stress-related symptoms and sleep changes were monitored. The authors found that L-Theanine supplementation helped improve sleep latency and disturbance, and reduced the amount of sleep medication required to help the individuals fall asleep.[6]

Is L-Theanine In Green Tea?  

L-Theanine is found in the leaves of the Camellia sinensis plant, which is used to make black, white, oolong, and green tea. 

A serving of commercially prepared tea contains approximately 6 mg of L-Theanine per gram.[7] A one-cup (240ml) serving of green tea, which usually contains 3-6 grams of tea depending on strength, translates to around 20-40 mg of L-Theanine.

How To Use L-Theanine For Sleep

One 2019 review notes that L-Theanine doses of between 200-400 mg/day for up to eight weeks in studies appear to be safe and beneficial for reducing anxiety and psychological stress.[8] 

An individual would need around 5 cups of tea to consume the 200 mg of L-Theanine used in most studies to improve anxiety and sleep. There are also plenty of L-Theanine supplements, most of which provide 200 mg per serving. 

Other Benefits Of L-Theanine

In addition to reducing feelings of stress and anxiety to support sleep, L-Theanine may offer these benefits: 

  • Improved focus. L-Theanine, combined with caffeine, may help improve focus and alertness during challenging mental tasks.[9]
  • Immune function. L-Theanine may help support the body’s natural immunity, and Green tea contains L-Theanine and antioxidants that may help prevent infections like the flu.[10][11] 
  • Anti-tumor effects. Some studies have found that L-Theanine can increase the anti-tumor activities of certain chemotherapy drugs. Research on L-Theanine and cancer has largely focused on green tea consumption.[12]

Side Effects of L-Theanine 

There are no major reported side effects of L-Theanine when consumed in the amounts found in teas and most supplements. The FDA lists L-Theanine as GRAS (generally recognized as safe) in doses of up to 250 mg per serving.[13]

L-Theanine And Other Medications/Supplements

L-Theanine is generally safe, but there are certain medications and supplements that shouldn’t be used at the same time. 


It’s prudent to avoid caffeinated teas, such as L-Theanine-containing green tea, with stimulating medications. L-Theanine can slow nervous system activity, whereas stimulants have the opposite effect. Some medications with stimulating effects include pseudoephedrine (Sudafed), epinephrine, and phentermine. L-Theanine may also disrupt the stimulating effects of cola, coffee, and energy drinks. 


L-Theanine should not be taken with blood pressure-lowering medications — such as diltiazem and losartan  — because it may cause it to drop too low. Certain supplements may also be used to reduce blood pressure and, therefore, should be avoided if taking L-Theanine, such as cat’s claw, fish oil, and Moringa oleifera.[14][15][16]

Should I Talk With My Doctor About L-Theanine?  

The L-Theanine content of tea consumed in moderate, regular amounts is unlikely to pose health risks. Speak with your healthcare provider before adding it in supplemental form to ensure it’s safe and appropriate. This is especially true if you’re using it to help improve a complaint like anxiety or poor sleep. 

The Last Word From Sleepopolis 

L-Theanine is an amino acid found in tea. Although it’s not an essential amino acid, it has been shown to help improve feelings of stress and anxiety. This is what links L-Theanine and sleep. The easiest way to add it to your diet is to consume green, black, white, oolong tea, or take an L-Theanine supplement. L-Theanine is not known to pose significant risks, but it’s always best to speak with your doctor before adding any new supplement.


  1. National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary Allowances. Recommended Dietary Allowances: 10th Edition. Washington (DC): National Academies Press (US); 1989. 6, Protein and Amino Acids. Available from: https://www.ncbi.nlm.nih.gov/books/NBK234922/ 
  2. White DJ, de Klerk S, Woods W, Gondalia S, Noonan C, Scholey AB. Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover Trial. Nutrients. 2016;8(1):53. Published 2016 Jan 19. doi:10.3390/nu8010053
  3. Rao TP, Ozeki M, Juneja LR. In Search of a Safe Natural Sleep Aid. J Am Coll Nutr. 2015;34(5):436-447. doi:10.1080/07315724.2014.926153
  4. Thiagarajah K, Chee HP, Sit NW. Effect of Alpha-S1-Casein Tryptic Hydrolysate and L-Theanine on Poor Sleep Quality: A Double Blind, Randomized Placebo-Controlled Crossover Trial. Nutrients. 2022;14(3):652. Published 2022 Feb 3. doi:10.3390/nu14030652
  5. Kim S, Jo K, Hong KB, Han SH, Suh HJ. GABA and L-Theanine mixture decreases sleep latency and improves NREM sleep. Pharm Biol. 2019;57(1):65-73. doi:10.1080/13880209.2018.1557698
  6. 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 Trial. Nutrients. 2019;11(10):2362. Published 2019 Oct 3. doi:10.3390/nu11102362
  7. Boros K, Jedlinszki N, Csupor D. Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples. Pharmacogn Mag. 2016;12(45):75-79. doi:10.4103/0973-1296.176061
  8. Lopes Sakamoto F, Metzker Pereira Ribeiro R, Amador Bueno A, Oliveira Santos H. Psychotropic effects of L-Theanine and its clinical properties: From the management of anxiety and stress to a potential use in schizophrenia. Pharmacol Res. 2019;147:104395. doi:10.1016/j.phrs.2019.104395
  9. Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-Theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-290. doi:10.1179/147683010X12611460764840
  10. Williams J, Kellett J, Roach PD, McKune A, Mellor D, Thomas J, Naumovski N. L-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion. Beverages 2016, 2(2), 13; https://doi.org/10.3390/beverages2020013
  11. Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC Complement Altern Med. 2011;11:15. Published 2011 Feb 21. doi:10.1186/1472-6882-11-15
  12. Shojaei-Zarghani S, Rafraf M, Yari-Khosroushahi A. Theanine and cancer: A systematic review of the literature. Phytother Res. 2021;35(9):4782-4794. doi:10.1002/ptr.7110
  13. GRN No. 209: L-Theanine. GRAS Notices. US Food and Drug Administration. Updated 30 Jan 2024. Accessed 12 Feb 2024. Available from: https://www.cfsanappsexternal.fda.gov/scripts/fdcc/index.cfm?set=GrASNotices&id=209 
  14. Yokogoshi H, Kato Y, Sagesaka YM, Takihara-Matsuura T, Kakuda T, Takeuchi N. Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats. Biosci Biotechnol Biochem. 1995;59(4):615-618. doi:10.1271/bbb.59.615
  15. Yoto A, Motoki M, Murao S, Yokogoshi H. Effects of L-Theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. J Physiol Anthropol. 2012;31(1):28. Published 2012 Oct 29. doi:10.1186/1880-6805-31-28
  16. Tabassum N, Ahmad F. Role of natural herbs in the treatment of hypertension. Pharmacogn Rev. 2011;5(9):30-40. doi:10.4103/0973-7847.79097
Lauren Panoff

Lauren Panoff

Lauren Panoff, MPH, RD is a Colorado-based health and nutrition writer who has been published with a number of trusted wellness platforms. She is a dietitian who specializes in plant-based living, as well as a mother of two humans and a dog.