Mood, stress and thinking
L-theanineand Cognitive performance
Both sources here measured higher cognitive performance.
How sure anyone can be
Low certainty, level 2 of 4Further research is likely to change this.
The most certain of the two findings here; each record carries its own.
The numbers reported
One source’s range, drawn against its own line of no difference and scaled to its own numbers.
0.250.51 standardised effect size0.77
This range stays on one side of the no-difference line.
Two sources, newest first
What we read is the published abstract, not the full paper, so a blank below may still be printed in the paper itself. A fixed rule worked this out from the source’s own fields. Nobody checked this rating by hand.
Systematic review, 2026
Low certainty, level 2 of 4Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.
Mol Psychiatry. 2026. doi:10.1038/s41380-026-03727-9. PMID:42410082.
- Number reported
- 0.51 standardised effect size
- Which way it went
- Higher
- Likely range
- 0.25 to 0.77
- Source’s own words
- standardised mean difference in choice reaction time
- Who was studied
- Adult
- Compared with
- placebo
- Amount taken
- 200 mg, single dose
- For how long
- 0 days
- Disagreement between studies
- Not in the abstract
- Kind of record
- Journal article
How this rating was reachedstarts at High, 2 steps down: risk of bias and imprecision
- Starts at High
- Risk of bias brought it down to Moderatethe abstract's own appraisal reports serious study limitationsReported in the abstract
- Imprecision brought it down to Lowthe abstract does not state how many participants were pooledNot in the abstract
- Ends at Low2 steps down.
- Checked, nothing to step it down for
- indirectness
- Inconsistency
- No disagreement reported, and no count of studies behind it
Imprecision stops at the first check that applies; others may apply too.
AI review could not confirm it — an AI agent re-read this finding against the saved source and at least one check failed. The batch record names the check and quotes the sentence that caused the doubt. No person read it.
Systematic review, 2025
Low certainty, level 2 of 4Effects 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 Trials.
Nutr Rev. 2025;83(10):1873-1891. doi:10.1093/nutrit/nuaf054. PMID:40314930.
- Number reported
- -0.35 standardised effect size
- Which way it went
- Higher
- Likely range
- -0.61 to -0.1
- Source’s own words
- standardized mean difference in choice reaction time vs placebo, first hour after intake; negative is shorter CRT
- Who was studied
- Healthy participants
- Compared with
- placebo
- Amount taken
- Not in the abstract
- For how long
- Not in the abstract
- Disagreement between studies
- Not in the abstract
- Kind of record
- Journal article
How this rating was reachedstarts at High, 2 steps down: risk of bias and imprecision
- Starts at High
- Risk of bias brought it down to Moderatethe abstract reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot in the abstract
- Imprecision brought it down to Lowthe abstract does not state how many participants were pooledNot in the abstract
- Ends at Low2 steps down.
- Checked, nothing to step it down for
- indirectness
- Inconsistency
- No disagreement reported, and no count of studies behind it
Imprecision stops at the first check that applies; others may apply too.
Source saved; quote checked byte-for-byte against it by software; no signature.
What is still missing from these readings
- Two do not say how many people took part.
- Amount taken — One of Two readings: Not in the abstract.
- For how long — One of Two readings: Not in the abstract.
Something nobody wrote down is never a zero and never a guess.
Still to read for L-theanine
Five of the 12 things on our list for L-theanine have no reading here yet:
- Alpha EEG power
- Diastolic blood pressure
- Heart rate variability (RMSSD)
- Resting heart rate
- Systolic blood pressure
Still to read means nobody here has got to it, not that it was tried and did nothing or that no research exists. A pairing on no list is not a gap: we never set out to read it.
Read next
L-theanine
Six other questions read for it
Mood, stress and thinking
34 questions read under it
Cognitive performance
12 other ingredients read against it
First six, alphabetical, and by nothing else. The rest are on Mood, stress and thinking.
This is a library, not advice. No recommendation, no dose, no diagnosis, no ranking. We never ask about your symptoms, and nothing here is tailored to you.