A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of…
Studies like this measure brain waves and cortisol after one dose in 16 people — what would an actual clinical benefit have to look like before you'd suggest I use this?
Suggestive but preliminary. Not settled. how we score evidence
Caveat on this rating: "This study and the journal's Rapid Service Fee was funded by Ethical Naturals Inc., California, USA", the company that sells the AlphaWave L-theanine tested; the trial was run at a contract research organisation. With 16 participants and one participant lost after period 1, the trial is far too small to support the conclusion in its own discussion that the product "should be considered as a nutraceutical supplement to manage acute stress."
L-theanine is sold in the US as a dietary supplement under the Dietary Supplement Health and Education Act of 1994 (DSHEA), and as a food additive it holds Generally Recognized as Safe (GRAS) status for use in beverages.
Sixteen moderately stressed healthy adults received a single 200 mg dose of branded L-theanine or placebo before a mental-arithmetic stress task. Frontal and whole-scalp alpha brain-wave power was higher three hours after the active dose and salivary cortisol fell more one hour after it. Sixteen people, one dose, and brain-wave and hormone readouts rather than any clinical outcome — this is a mechanism demonstration, not evidence that L-theanine reduces anxiety in daily life.
Worth asking
Studies like this measure brain waves and cortisol after one dose in 16 people — what would an actual clinical benefit have to look like before you'd suggest I use this?
Source
A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave L-Theanine on Stress in a Healthy Adult Population. — Evans M, McDonald AC, Xiong L, Crowley DC, Guthrie N. (2021)
Indexed peer-reviewed journal
Read the source: https://doi.org/10.1007/s40120-021-00284-x
DOI: 10.1007/s40120-021-00284-x
How this was scored
- Study design
- Randomised controlled trial
- Funding
- Industry funded
- Published in
- Indexed peer-reviewed journal
- Sample size
- 16
- Preregistered
- Yes
- Conflicts disclosed
- Yes
- Independent of proponent
- No
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published August 19, 2026.
Questions
How strong is the evidence behind this?
Resolv rates this source "early signal". Suggestive but preliminary. Not settled. It scores 48 out of 100 on our published rubric. One caveat travels with that badge: "This study and the journal's Rapid Service Fee was funded by Ethical Naturals Inc., California, USA", the company that sells the AlphaWave L-theanine tested; the trial was run at a contract research organisation. With 16 participants and one participant lost after period 1, the trial is far too small to support the conclusion in its own discussion that the product "should be considered as a nutraceutical supplement to manage acute stress." The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave L-Theanine on Stress in a Healthy Adult Population. — Evans M, McDonald AC, Xiong L, Crowley DC, Guthrie N. (2021). Published in: Indexed peer-reviewed journal. DOI: 10.1007/s40120-021-00284-x. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Randomised controlled trial. Funding: Industry funded. The researchers were not independent of whoever benefits from the result. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is l-theanine, theanine, suntheanine, alphawave, gamma-glutamylethylamide, green tea amino acid FDA approved for this use?
No. Its current status is: Not FDA-evaluated for this use. L-theanine is sold in the US as a dietary supplement under the Dietary Supplement Health and Education Act of 1994 (DSHEA), and as a food additive it holds Generally Recognized as Safe (GRAS) status for use in beverages.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.