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L-theanine
An amino acid found mainly in tea leaves and sold on its own as a supplement. People take it for stress, sleep and focus, sometimes with caffeine.
Explained simply · Last reviewed
What it is
L-theanine is an amino acid found mainly in tea leaves. EFSA, the EU food safety agency, says it is present mainly in the tea plant, where it makes up about half of the amino acids in tea, and that it has also been reported in a mushroom. A 2025 review says it was first isolated from green tea in 1949, has been used for thinking and mood, and is now also sold in purified form as a food supplement.
More about L-theanine
EFSA, the EU food safety agency, says it is present mainly in the tea plant, where it makes up about half of the amino acids in tea, and that it has also been reported in a mushroom. A 2025 review says it was first isolated from green tea in 1949, has been used for thinking and mood, and is now also sold in purified form as a food supplement.
In the United States, FDA has answered several notices from companies that concluded L-theanine is generally recognized as safe (GRAS) for use in foods. Its 2026 letter lists earlier notices for L-theanine extracted from tea leaves and for chemically synthesized L-theanine. The 2026 notice covers L-theanine made by fermentation with genetically engineered bacteria. Each time, FDA said it had no questions about the company's conclusion. Its 2026 letter states that it is not an affirmation that L-theanine is GRAS. The letter is about L-theanine as an ingredient in listed food categories; it does not address L-theanine sold as a supplement.
In the European Union, EFSA assessed proposed claims in 2011 that L-theanine from tea helps thinking, stress, sleep and menstrual discomfort; the claims below report what it found. A 2025 review of trials in healthy people says most were run in a laboratory and few used tea or amounts of theanine like those in tea. A 2024 review gathered trials in people with mental health conditions, where L-theanine was often added to their usual medicines.
Also known as: theanine, γ-glutamylethylamide
At a glance
Safety: known risks. See Safety ↓Claims made about L-theanine, and how strong the evidence is for each:
- Reduces stress or anxietyEvidence rating: Limited
- Improves sleepEvidence rating: Limited
- Improves attention, reaction time or other thinking skills when taken on its ownEvidence rating: Limited
- Improves attention when taken together with caffeineEvidence rating: Limited
- Eases symptoms of schizophrenia, depression or obsessive-compulsive disorder when added to medicationEvidence rating: Limited
- Improves ADHD symptoms in childrenEvidence rating: Insufficient
- Eases premenstrual symptomsEvidence rating: Insufficient
Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate
Safety
Read this before the ratings below.
Risks
- A 2024 systematic review of 11 trials in people with mental health conditions lists side effects reported in trials that added L-theanine to medicines for obsessive-compulsive disorder, depression or schizophrenia, among them nausea, abdominal pain, headache, irritability, diarrhea and constipation. For the obsessive-compulsive disorder and depression trials, it reports no significant difference in side effects between L-theanine and placebo. Those trials had about 50 to 60 people each, which is too little evidence to show a difference either way.
- The same review describes several of its trials as finding L-theanine well tolerated, with no significant adverse events. One trial in boys with ADHD reported a single minor side effect, a facial tic.
- A 2025 meta-analysis of five placebo-controlled trials in healthy adults, each giving single doses to between 20 and 50 people, records no adverse events in any of them.
- EFSA states that its 2011 opinion on L-theanine health claims is not a positive assessment of its safety.
- In 2026, the US Food and Drug Administration (FDA) said it had no questions about a company’s conclusion that L-theanine made by fermentation is generally recognized as safe (GRAS) as an ingredient in the foods listed in its notice, which excludes infant formula and foods for infants and toddlers. FDA states that its letter is not an affirmation that L-theanine is GRAS, and that manufacturers are responsible for ensuring their products are safe.
Safety sources: Source [1]Source [2]Source [3]Source [4]
What the evidence says
Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.
Reduces stress or anxiety Evidence rating: Limited
People take it hoping it will help them feel calmer and less stressed.
One review reports less anxiety in four small trials; another found relaxation results uncertain, one anxiety-disorder trial found no benefit, and EFSA found a stress benefit not established.
This claim covers everyday stress and anxiety, and anxiety disorders. A 2025 systematic review of green tea and its compounds for mood found four small placebo-controlled trials of L-theanine on its own, three of them testing single doses. Its authors say L-theanine "consistently reduced anxiety" across them, on scales of tension, anxiety and perceived stress. They judged none of the 13 trials in their review at low risk of bias overall. They add that definitive conclusions "cannot be drawn from individual studies alone".
A 2025 meta-analysis of trials in healthy people writes that L-theanine "may improve feelings of relaxation compared to placebo". But only two trials could be pooled, and their results were consistent both with no difference and with a difference favoring placebo. The reviewers call this a high degree of uncertainty.
A 2024 systematic review of trials in people with mental health conditions found one trial in generalized anxiety disorder, with 46 participants. As the review describes it, L-theanine did not reduce anxiety more than placebo. Yet the review's conclusion lists anxiety disorders among the conditions where L-theanine reduced symptoms more than control. This page reports both and does not settle the difference. The same review describes a trial in children with tics, of L-theanine with vitamin B6 against psychoeducation, that found no difference in anxiety.
EFSA, the EU food safety agency, assessed a claim in 2011 that L-theanine from tea eases psychological stress. It found no references from which conclusions could be drawn, and concluded that a cause and effect relationship had not been established. It set aside two small trials, both also counted by the green tea review, because they measured anxiety rather than stress directly.
Part of the 2025 meta-analysis's funding came from a tea company, and two of its authors work for tea companies. The sources disagree, so this page takes the lower reading and rates the claim limited: a few small trials, with results that range from less anxiety to no difference from placebo.
Improves sleep Evidence rating: Limited
People take it at night hoping it will help them fall asleep and sleep better.
A 2025 review called the evidence on sleep inconclusive; trials in adults and children were small and mixed, and EFSA found a sleep benefit not established.
A 2025 meta-analysis of trials in healthy people could not pool the sleep studies, so it described them one by one. It calls the evidence on sleep inconclusive. In one trial in adults, people taking L-theanine for four weeks reported falling asleep faster, fewer sleep disturbances and less use of sleep medicine than with placebo, on a sleep questionnaire. Three small trials in students found no significant difference in reported sleep time between green tea, theanine and placebo.
In boys with ADHD, one trial found better sleep with L-theanine than placebo when sleep was measured by a wrist-worn monitor, but no improvement on sleep questionnaires. Both the 2025 meta-analysis and a 2024 systematic review of trials in mental health conditions describe this trial. The 2024 review also describes a trial in adults with sleep problems in which sleep scores improved with both L-theanine and placebo. The reviewers' own comparison found no significant difference between the two.
For a trial in generalized anxiety disorder, the 2024 review's text and table disagree. The text says insomnia symptoms were lower with L-theanine at each visit, "although this was not reflected in a significant Group × Time interaction". The table says L-theanine "improved sleep satisfaction". This page reports both and does not settle the difference.
EFSA, the EU food safety agency, assessed a claim on maintaining normal sleep in 2011. It found no references from which conclusions could be drawn, and concluded that a cause and effect relationship had not been established.
Part of the 2025 meta-analysis's funding came from a tea company, and two of its authors work for tea companies. This page rates the claim limited: a few small trials, with mixed results.
Sources: Source [1]Source [2]Source [3]
Improves attention, reaction time or other thinking skills when taken on its own Evidence rating: Limited
People take it hoping it will sharpen their focus and help them think faster.
Reviews of small trials in healthy adults found faster responses on some tasks and none on others, at low to very low certainty in the graded one; EFSA found a benefit not established.
This claim is about short-term test scores in healthy adults, measured about 40 to 70 minutes after a single dose. A 2025 meta-analysis pooled five placebo-controlled trials with 148 healthy adults. L-theanine made no significant difference to simple reaction time or to the Stroop test, a color-word task. Responses on visual processing tasks were faster only when the analysis used the higher-dose arms of one trial. The reviewers rated how sure they could be (certainty) low for three outcomes and very low for one Stroop outcome.
The reviewers conclude that the benefit "could not be confirmed by all test methods", and that superiority over placebo "is not proven". They also write that their analysis "partially supports" its use for thinking skills. They call for larger trials using standardized products.
A 2025 meta-analysis of trials in healthy people shares several of the same trials. With L-theanine alone, it found "small-to-moderate differences favoring theanine" on choice reaction time in the first hour, though the range of likely effects also took in little or no difference. Most other tasks showed little or no difference. Its authors say theanine alone "may improve" performance on two tasks, but that little or no difference, or a difference favoring placebo, could not always be ruled out. It did not grade certainty. Part of its funding came from a tea company, and two of its authors work for tea companies.
EFSA, the EU food safety agency, assessed a claim on improving cognitive function in 2011. It found three trials it could draw conclusions from, and none showed an improvement. In two, reaction times were slower after L-theanine than after placebo; in the third, L-theanine impaired one arithmetic task. It concluded that a cause and effect relationship had not been established. This page rates the claim on the lowest certainty the graded review gives these outcomes, very low.
Sources: Source [1]Source [2]Source [3]
Improves attention when taken together with caffeine Evidence rating: Limited
People take it with coffee or caffeine hoping the pair will sharpen their focus.
A 2025 review found small gains in attention-task accuracy with theanine plus caffeine over placebo, but many results were uncertain and the review did not grade certainty.
This claim is about the combination, not L-theanine alone, and about test scores within two hours of a single dose. A 2025 meta-analysis of trials in healthy people compared theanine plus caffeine with placebo. It found small-to-moderate gains in accuracy on an attention-switching task in the first and second hours. On a sustained attention task, it found a small gain in accuracy in the second hour, though the range of likely effects ran from little or no difference to a small-to-moderate one. Simple reaction time was faster in the second hour, from three trials. The reviewers conclude that the combination "likely improves performance in attentional tasks" and "may benefit mood outcomes such as alertness and overall mood".
Other results were less clear. For choice reaction time, alertness and overall mood, the range of likely effects included no difference. For alertness, the reviewers say future studies may find no difference, or a difference either way. None of the trials they assessed was judged at low risk of bias. The reviewers also note that an earlier meta-analysis concluded that any benefit of the combination for attention is likely due to caffeine.
Part of the review's funding came from a tea company, and two of its authors work for tea companies. The review reports that industry was also the most common funder of the trials in its pooled analyses. It did not grade certainty, so this page rates the claim limited on what it reports: a few small trials, with mixed results.
Sources: Source [1]
Eases symptoms of schizophrenia, depression or obsessive-compulsive disorder when added to medication Evidence rating: Limited
People living with a mental health condition take it hoping it will add to the effect of their medication.
A 2024 review found lower scores on some symptom scales, not all, when L-theanine was added to medication in small trials, mostly one per condition, and says further studies are essential.
This claim is about L-theanine added to medicines, not taken instead of them. A 2024 systematic review gathered 11 randomized trials in mental health conditions. In schizophrenia or schizoaffective disorder, trials adding L-theanine to antipsychotics reported lower scores than placebo on some symptom scales, but not on others. One of these trials reports on part of the same participants as another. Another combined L-theanine with a second compound, pregnenolone.
In depression, the review reports one trial that randomized 60 people taking the antidepressant sertraline to L-theanine or placebo for six weeks. Depression scores fell more with L-theanine. In obsessive-compulsive disorder, it reports one trial of 50 adults that added L-theanine or placebo to fluvoxamine for ten weeks. Its table gives lower total symptom scores than placebo at weeks 5 and 10, with more complete responses, as the trial defined them; its text gives the same week 5 and 10 results for obsession scores. Compulsion scores did not differ significantly.
The reviewers describe the studies as scarce and say further studies are essential to validate the findings. They list potential publication bias and a lack of standard doses among the review's limits. This page rates the claim limited: mostly one small trial per condition.
Sources: Source [1]
Improves ADHD symptoms in children Evidence rating: Insufficient
Parents give it to children with ADHD hoping it will help with focus and restlessness.
A 2024 review found only two small trials in boys with ADHD: one measured sleep, and one tested attention in five boys on single days.
A 2024 systematic review of trials in mental health conditions found two trials in children with ADHD, both in boys. One measured sleep. With L-theanine, sleep measured by a wrist-worn monitor was better than with placebo. The review adds that the sleep questionnaire results did not correlate with the monitor results. The other gave five boys L-theanine, caffeine, both, or placebo on single test days. With L-theanine alone, overall thinking scores improved but inhibitory control appeared to worsen. The reviewers say the combination with caffeine showed potential to improve both.
The review's conclusion lists ADHD among the conditions where L-theanine reduced symptoms more than control. As the review describes them, the two trials measured sleep and test performance, not ADHD symptoms. This page rates the claim insufficient: too little research on ADHD symptoms to say either way.
Sources: Source [1]
Eases premenstrual symptoms Evidence rating: Insufficient
People take it hoping it will ease the tension and discomfort before a period.
EFSA assessed this claim in 2011, found no study it could draw conclusions from, and concluded that a cause and effect relationship had not been established.
EFSA, the EU food safety agency, assessed a proposed claim in 2011 that L-theanine from tea reduces menstrual discomfort in women with premenstrual syndrome. Of the studies it was given, one was in Japanese with no translation available. The one conference abstract on premenstrual syndrome gave too little information on design, methods and statistics for a full evaluation. EFSA concluded that a cause and effect relationship had not been established.
None of the reviews cited on this page reports a trial in premenstrual syndrome, so this page rates the claim insufficient.
Sources: Source [1]
Which form the evidence used
Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.
L-theanine supplements, What the sources supportDetails
The five trials pooled in the cited 2025 meta-analysis on thinking skills gave L-theanine as capsules, as a powder or dissolved in water. A 2025 review of trials in healthy people notes that the trials it lists used synthetic L-theanine unless they say otherwise. FDA’s 2026 letter lists earlier notices for L-theanine extracted from tea leaves and for chemically synthesized L-theanine, and its own notice covers L-theanine made by fermentation. None of the cited sources compared forms of L-theanine with each other, so this page cannot compare them. Source [1]Source [2]Source [3]
Tea, Details
EFSA, the EU food safety agency, states that theanine makes up 1–2% of the dry weight of tea leaves. It judged tea itself not sufficiently characterized for the claims it assessed, because the type of tea, how it was made and how it was brewed were not described. A 2025 review of trials in healthy people notes that few trials used tea or amounts of theanine like those in tea, and that no trial in its analyses of theanine alone gave it as tea or a tea-flavored drink. Source [1]Source [2]
Sources
- The Impact of Green Tea and Its Bioactive Compounds on Mood Disorder Symptomology and Brain Derived Neurotrophic Factor: A Systematic Review of Randomized Controlled TrialsBiomedicines, 2025 · Systematic review · Primary source
- Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled TrialsNutrition Reviews, 2025 · Meta-analysis · Primary source
- The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic reviewBMC Psychiatry, 2024 · Systematic review · Primary source
- Scientific Opinion on the substantiation of health claims related to L-theanine from Camellia sinensis (L.) Kuntze (tea) and improvement of cognitive function (ID 1104, 1222, 1600, 1601, 1707, 1935, 2004, 2005), alleviation of psychological stress (ID 1598, 1601), maintenance of normal sleep (ID 1222, 1737, 2004) and reduction of menstrual discomfort (ID 1599) pursuant to Article 13(1) of Regulation (EC) No 1924/2006EFSA Panel on Dietetic Products, Nutrition and Allergies (EFSA Journal), 2011 · Health authority summary · Primary source
- Promising, but Not Completely Conclusive—The Effect of l-Theanine on Cognitive Performance Based on the Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical TrialsJournal of Clinical Medicine, 2025 · Meta-analysis · Primary source · Certainty: very low
- GRAS Notice (GRN) 1311 Agency Response LetterU.S. Food and Drug Administration, 2026 · Health authority summary · Primary source
Page history
Show all 2 changes to this page
- — Published.
- — First drafted. Stress or anxiety, sleep, thinking skills on its own, attention with caffeine, and symptoms of mental health conditions when added to medication rated limited; ADHD symptoms in children and premenstrual symptoms rated insufficient.