The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a…
The whole L-theanine literature is nine small trials in stressed volunteers — is that enough for you to recommend it, or is it something to try only alongside proper treatment?
Reasonable evidence with real limitations. how we score evidence
Caveat on this rating: The review did not pool the trials or grade certainty of evidence, so "may assist" is a narrative judgement rather than a measured effect; none of the nine trials studied people with a diagnosed anxiety disorder, and several were manufacturer-funded.
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.
A PRISMA-guided systematic review found only nine peer-reviewed randomized controlled trials of pure supplemental L-theanine against a control for stress or anxiety in humans. The authors concluded 200-400 mg per day "may assist" in reducing stress and anxiety in people exposed to stressful conditions, while stating plainly that longer-term and larger-cohort studies are needed before L-theanine can be clinically justified as a therapeutic agent. Nine small trials is the entire evidence base.
Worth asking
The whole L-theanine literature is nine small trials in stressed volunteers — is that enough for you to recommend it, or is it something to try only alongside proper treatment?
Source
The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review. — Williams JL, Everett JM, D'Cunha NM, et al. (2020)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1007/s11130-019-00771-5
DOI: 10.1007/s11130-019-00771-5
How this was scored
- Study design
- Systematic review of randomised trials
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- not recorded
- Preregistered
- No
- Conflicts disclosed
- No
- Independent of proponent
- not recorded
- 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 "moderate evidence". Reasonable evidence with real limitations. It scores 62 out of 100 on our published rubric. One caveat travels with that badge: The review did not pool the trials or grade certainty of evidence, so "may assist" is a narrative judgement rather than a measured effect; none of the nine trials studied people with a diagnosed anxiety disorder, and several were manufacturer-funded. 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?
The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review. — Williams JL, Everett JM, D'Cunha NM, et al. (2020). Published in: Reputable peer-reviewed journal. DOI: 10.1007/s11130-019-00771-5. 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: Systematic review of randomised trials. Funding: Funding not disclosed. Independence from the proponent is not recorded. 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.