L-Theanine Guide (2026): Research, Dose & Caffeine Pairing
By Erin Rose Updated October 7, 2026 Sources
In small trials in healthy adults, one dose of L-theanine, most often 200 mg, changed some attention and stress-test scores a little; other tests showed no change. L-theanine is an amino acid found in tea. Several trials had ties to tea or L-theanine companies. If you try it, 200 mg is the dose trials used most.
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What L-theanine is
- An amino acid from tea. It is not one of the amino acids that build protein. Suntheanine (made by Taiyo Kagaku) and AlphaWave are two branded versions of the same molecule.
- How much. No U.S. agency sets a dose. Health Canada’s L-theanine monograph lists 200 to 250 mg a day for adults. One-dose trials used 50 to 400 mg; 200 mg was the most common. How much to take.
What the trials measured
Here is each trial in healthy adults we read on PubMed, with its dose, what it measured and its ties to industry (from each record’s author addresses, conflict-of-interest statement and grants). Every one compared L-theanine with a dummy pill (placebo).
| Study | Dose and measure | What it found |
|---|---|---|
| Nobre 2008Healthy young adults | 50 mgAlpha brain waves at rest (EEG) | Alpha activity rose more than with a dummy pill. That is a brain-wave reading, not a feelingTies: First author at Unilever (PubMed address); no funder named |
| Kimura 200712 adults | Dose not reported in the abstractHeart rate and a saliva marker during a mental-math task | Heart rate and the saliva marker rose less than with a dummy pillTies: The record names no company; two co-authors (Ozeki, Juneja) are Taiyo Kagaku staff on other papers |
| Lu 200416 healthy adults | 200 mgAnxiety ratings during a lab test meant to make people anxious | No change against a dummy pill (a prescription drug tested beside it showed none either)Ties: None named on PubMed |
| Dassanayake 202332 young adults | 100, 200 or 400 mgReaction time and attention tasks | 100 and 200 mg sped a simple reaction-time test by about 16 thousandths of a second; 400 mg and the harder tasks showed no clear changeTies: None named on PubMed |
| Dassanayake 202227 young adults | 100, 200 or 400 mgA brain-signal (EEG) timing measure during an attention task | Only 400 mg changed it; reaction time did not change at any doseTies: None named on PubMed |
| Trial | Dose and measure | What it found |
|---|---|---|
| Hidese 201930 healthy adults (crossover) | 200 mg a day for 4 weeksMood, stress and sleep-quality questionnaires | Scores were lower after 4 weeks of L-theanine; some sleep sub-scores were lower than with the dummy pillTies: Taiyo Kagaku (maker of Suntheanine) supplied the tablets; two authors work there |
| Moulin 202430 healthy adults with moderate stress | 400 mg a day for 28 daysA stress questionnaire and saliva cortisol, at day 14 and day 28 | Stress scores fell in both the L-theanine and the dummy-pill groups; cortisol did not differTies: Run by a contract research firm, with an author from the maker of AlphaWave, the L-theanine tested |
Reviews: a 2026 review of 31 trials found one 200 mg dose sped a choice reaction-time test (Gerolymos 2026; one author founded a supplement company). A 2020 review of 9 trials of stress ratings calls for longer, larger studies (Williams 2020).
L-theanine with caffeine
Many trials gave L-theanine with caffeine. They used pairs from about 0.8:1 to 2.4:1 L-theanine to caffeine, not one fixed ratio. None compared one ratio with another.
| Study | Dose and ratio | What it found |
|---|---|---|
| Owen 200827 healthy adults | 100 mg + 50 mg caffeine2:1 | The pair improved speed and accuracy on the task an hour later, against a dummy pillTies: First author at Unilever (PubMed address); no funder named |
| Giesbrecht 201044 young adults | 97 mg + 40 mg caffeine2.42:1 | Both improved against a dummy pillTies: First author at Unilever (PubMed address); no funder named |
| Haskell 2008Healthy young adults | 250 mg + 150 mg caffeine1.67:1 | The pair sped some reaction-time tests, improved some accuracy scores and lowered “headache” and “tired” ratings. L-theanine alone raised “headache” ratings and lowered scores on a counting-backwards taskTies: None named on PubMed |
| Kahathuduwa 201720 healthy men | 200 mg + 160 mg caffeine1.25:1 | L-theanine, caffeine and the pair each sped it against a dummy pillTies: None named on PubMed |
| Rogers 200848 adults | 200 mg + 250 mg caffeine0.8:1 | L-theanine blunted the rise in blood pressure from caffeine. It did not change jitteriness, alertness or mood, and it slowed reaction time on one taskTies: None named on PubMed |
A 2014 review of 11 studies found moderate gains in self-rated alertness and task-switching accuracy in the first 2 hours after caffeine plus L-theanine (Camfield 2014). Doses with caffeine.
Sleep
A 2025 review pooled 12 studies of self-rated sleep quality and found a modest gain, with a wide margin of error. Its trials mixed people of all ages and health, and few gave L-theanine on its own (Bulman 2025). A 2015 article often cited for sleep is a review by three Taiyo Kagaku staff, not a trial (Rao 2015).
How long the trials ran
Most trials were one dose, with testing 20 to 90 minutes later. The two daily trials both ran about 4 weeks (28 days). Only one measured partway, at day 14, and its stress scores fell with the dummy pill too (Moulin 2024).
Which L-theanine is third-party tested
Of the 24 L-theanine products we score, 3 are on a public testing list we checked on October 7, 2026: Momentous, Thorne and the OLLY L-theanine gummy blend (50 mg of L-theanine with GABA and lemon balm). The listings, all 24 we score and prices by bottle size.
L-theanine guides
Which product
How much
Side effects and cautions
- In trials. In one one-dose trial, 250 mg of L-theanine alone raised “headache” ratings (Haskell 2008). One 28-day trial in 30 adults at 400 mg a day reported no clinically relevant problems; staff of the L-theanine maker were authors (Moulin 2024).
- No upper limit. We found no upper limit for L-theanine set by a national health agency.
- Medical conditions. Small trials in people with medical conditions exist. Ask a doctor.
- Ask your doctor first if you take any medicine, are pregnant or breastfeeding, or are buying it for a child.
We read 29 L-theanine products and could score 24 (every score, and why some are not scored). Prices are each brand’s own list price; other stores may differ.
Sources
- Nobre AC 2008, Asia Pacific journal of clinical nutrition. PubMed 18296328
- Kimura K 2007, Biological psychology. PubMed 16930802
- Lu K 2004, Human psychopharmacology. PubMed 15378679
- Dassanayake TL 2023, Nutritional neuroscience. PubMed 36263942
- Dassanayake TL 2022, Nutritional neuroscience. PubMed 32777998
- Owen GN 2008, Nutritional neuroscience. PubMed 18681988
- Giesbrecht T 2010, Nutritional neuroscience. PubMed 21040626
- Haskell CF 2008, Biological psychology. PubMed 18006208
- Kahathuduwa CN 2017, Nutritional neuroscience. PubMed 26869148
- Rogers PJ 2008, Psychopharmacology. PubMed 17891480
- Hidese S 2019, Nutrients. PubMed 31623400
- Moulin M 2024, Neurology and therapy. PubMed 38758503
- Camfield DA 2014, Nutrition reviews. PubMed 24946991
- Williams JL 2020, Plant foods for human nutrition (Dordrecht, Netherlands). PubMed 31758301
- Bulman A 2025, Sleep medicine reviews. PubMed 40056718
- Gerolymos C 2026, Molecular psychiatry. PubMed 42410082
- Rao TP 2015, Journal of the American College of Nutrition. PubMed 25759004
- Health Canada, Natural Health Product Monograph: L-Theanine (dated January 30, 2026), read October 7, 2026. Monograph
- Testing lists: NSF/ANSI 173, NSF Certified for Sport, Informed Choice and Informed Sport, read October 7, 2026; USP Verified from our copy of September 22, 2026. Labels: each brand’s page or the NIH Dietary Supplement Label Database. Prices: each brand’s own list price, checked October 7, 2026.
This page is for information. It is not medical advice.