L-theanine
An amino acid from the tea plant, Camellia sinensis
An amino acid found mainly in tea leaves, often taken with caffeine, and studied mostly for attention, stress and sleep. Here is every study in people we could find, sorted from each study's summary.
- Found in: tea leaves
- Most tested: 200 mg
- Often a single dose
From every paper to the studies that matter
Most research on L-theanine is in the lab or about tea itself. Only a small share tests it in people, and that is what this page is about.
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1,277 papers mention L-theanine. Every record in PubMed, all years
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115 are about people. The rest: 426 lab and animal studies, 164 reviews, 572 on chemistry, farming and more
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51 give L-theanine on its own. 61 more test it with caffeine or inside a blend
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40 are randomised against a placebo. The strongest kind of study
Bar lengths use a square-root scale so the small numbers stay visible.
How much research there is
- 51 studies giving L-theanine to people
- 40 of them randomised against a placebo
- 1,746 people taking part, where studies say
- 22 systematic reviews pooling the trials
Studies in people, by year published
L-theanine on its own.
What the studies looked at
Each study can measure several things. Choose a topic to see its studies in the list below.
Studies in people with a diagnosed condition are counted here and listed with their population. We describe what they measured, not what they might treat. Most studies also report safety; see below.
What was tested, and how much
L-theanine is a single compound, so milligrams compare directly from one study to the next. Many studies gave one dose shortly before testing.
Daily amount, one dot per study
Studies per extract
Named extracts are the maker's brand. "Not named" means the study didn't say.
All studies in people
Filter the list, then open a study on PubMed. Each row comes from the study's published summary.
| Study | Who took part | People | Extract and daily dose | Length |
|---|---|---|---|---|
| Yamaura 2026Single-arm or open-label | Healthy adults | 39 | Not named, 300 mg | – |
| Deshpande 2025RCT, active or other control | Preoperative surgical patients | 168 | Not named | – |
| Karunaratne 2025Crossover, placebo | Sleep-deprived healthy young adults | 24 | Not named, 200 mg | – |
| Tuncer 2025Crossover, placebo | Trained competitive athletes | 20 | Not named, 200 mg | – |
| Razazan 2025Crossover, placebo | Elite male wrestlers | 12 | Not named | – |
| Kurdi 2024RCT, placebo | Cancer patients with insomnia | 120 | Not named, 200 mg | 2 weeks |
| McAllister 2024RCT, placebo | Healthy young adults under mental stress challenge | 80 | Not named, 200 mg | – |
| Moulin 2024RCT, placebo | Healthy adults with moderate stress | 30 | AlphaWave L-Theanine, 400 mg | 4 weeks |
| Lim 2024Non-randomised controlled | Female college archers in competition | 18 | Not named | – |
| Zhong 2024Pharmacokinetic | Healthy volunteers | – | Not named, 400 mg | – |
| Imafuku 2023RCT, active or other control | Adults with sleep problems | 160 | Not named, 200 mg | – |
| Shamabadi 2023RCT, placebo | Chronic schizophrenia inpatients on risperidone | 80 | Not named, 400 mg | 8 weeks |
| Shamabadi 2023RCT, placebo | Adults with major depressive disorder on sertraline | 60 | Not named, 200 mg | 6 weeks |
| Nematizadeh 2023RCT, placebo | Adults with moderate to severe OCD on fluvoxamine | 60 | Not named, 200 mg | 10 weeks |
| Dassanayake 2023Crossover, placebo | Healthy young adults | 32 | Not named | – |
| Yilmaz 2023Crossover, placebo | Elite national curling athletes | 22 | Not named | – |
| Baba 2023Crossover, placebo | Healthy young women | – | Not named, 50 mg | – |
| Furushima 2022RCT, placebo | Healthy young adults | 120 | Not named, 200 mg | – |
| Dassanayake 2022Crossover, placebo | Healthy young adults | 27 | Not named | – |
| Baba 2021RCT, placebo | Healthy Japanese adults aged 50-69 | – | Not named | 12 weeks |
| Yuan 2021Other | Not stated in record (empty abstract) | – | Not named | – |
| Evans 2021Crossover, placebo | Healthy moderately stressed adults | – | AlphaWave L-Theanine, 200 mg | – |
| Williams 2020RCT, placebo | Healthy adult males | 18 | Not named, 200 mg | – |
| Kahathuduwa 2020Crossover, placebo | Boys with ADHD aged 8-15 | 5 | Not named | – |
| Sarris 2019RCT, placebo | Adults with generalised anxiety disorder on antidepressants | 46 | Not named | 8 weeks |
| Hidese 2019Crossover, placebo | Healthy adults without psychiatric illness | 30 | Not named, 200 mg | 4 weeks |
| Juszkiewicz 2019RCT, placebo | Elite rowers | 20 | Not named, 150 mg | 6 weeks |
| Kahathuduwa 2018Crossover, placebo | Healthy adult men | 9 | Not named, 200 mg | – |
| Giles 2017Crossover, placebo | Healthy adults | 36 | Not named, 200 mg | – |
| Kahathuduwa 2017Crossover, placebo | Healthy adult men | 20 | Not named, 200 mg | – |
| Hidese 2017Single-arm or open-label | Adults with major depressive disorder | 20 | Not named, 250 mg | 8 weeks |
| Dodd 2015Crossover, placebo | Healthy caffeine consumers and non-consumers | 24 | Not named, 50 mg | – |
| Ota 2015Single-arm or open-label | Patients with chronic schizophrenia | 17 | Not named, 250 mg | 8 weeks |
| Ota 2014Crossover, placebo | Healthy adults | 14 | Not named | – |
| Ross 2014Other | Not stated in record | – | Suntheanine | – |
| Unno 2013RCT, placebo | Pharmacy students under practice stress | 20 | Not named, 400 mg | 2 weeks |
| Foxe 2012Crossover, placebo | Healthy adults | 27 | Not named, 100 mg | – |
| Yoto 2012Crossover, placebo | Healthy adults under stress tasks | 14 | Not named | – |
| Scheid 2012Pharmacokinetic | Healthy adults | 12 | Not named, 100 mg | – |
| Lyon 2011RCT, placebo | Boys aged 8-12 with ADHD | 98 | Suntheanine, 400 mg | 6 weeks |
| Ritsner 2011RCT, placebo | Adults with schizophrenia or schizoaffective disorder | 60 | Not named, 400 mg | 8 weeks |
| Miodownik 2011RCT, placebo | Adults with schizophrenia or schizoaffective disorder | 40 | Not named, 400 mg | 8 weeks |
| Gomez-Ramirez 2009Crossover, placebo | Healthy adults | 13 | Not named, 250 mg | – |
| Rogers 2008RCT, placebo | Healthy adults | 48 | Not named, 200 mg | – |
| Nobre 2008RCT, placebo | Healthy young adults | 35 | Not named, 50 mg | – |
| Haskell 2008Crossover, placebo | Healthy adults | – | Not named, 250 mg | – |
| Kelly 2008Crossover, placebo | Healthy adults | – | Not named, 100 mg | – |
| Kimura 2007Crossover, placebo | Healthy adults under mental stress task | 12 | Not named | – |
| Gomez-Ramirez 2007Other | Study volunteers | – | Not named | – |
| Lu 2004Crossover, placebo | Healthy volunteers | 16 | Not named, 200 mg | – |
| Yagyu 1997Crossover, placebo | Healthy young men | 20 | Not named, 200 mg | – |
What's known about safety
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In trials
No serious side effects were reported in a review of 31 placebo-controlled trials. Trials have used up to 900 mg a day.
Gerolymos 2026, review of 31 trials; Cotter 2025, 13 sleep trials at 50 to 900 mg a day
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In the UK
L-theanine extracted from tea can be sold in food supplements. We found no official UK or EU upper limit.
EU Novel Food Status Catalogue; FSA novel foods guidance; searches of EFSA, FSA and COT, Oct 2026
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Check first
It hasn't been studied in pregnancy or breastfeeding, and how it mixes with medicines isn't well studied. Speak to a pharmacist or doctor first if either applies to you.
No trials or UK guidance found, Oct 2026
Where these studies come from
We list every published study of L-theanine in people. This first version is built from each study's summary; full-paper checks come next.
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We search
PubMed, the world's main library of medical research, for every paper on L-theanine.
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We keep studies in people
Lab and animal work is counted but left out of the list, because it doesn't tell you what happens in people.
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We note the basics
Who took part, how many, how much and for how long, from each study's published summary. A second check corrects what the first read gets wrong.
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We read them in full
Results appear once we've read the whole paper and checked every number. The date at the top shows when this entry was last updated.
Download the study list
Every study in people as a spreadsheet, 51 rows, free to reuse with a link back.
Versions
Each update to the data gets a new version number, so you can tell what changed and when.
See every version
1.0 · 19 Oct 2026. First release. Every published study giving L-theanine on its own to people is listed from its summary. None is read in full yet.
