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Open WellbeingWhat the studies actually measured

Mood, stress and thinking

L-theanineand Anxiety

Only one source here so far, and it found no clear difference in anxiety.

How sure anyone can be

Low certainty, level 2 of 4

Further research is likely to change this.

The numbers reported

No number has been put on this yet. One source recorded only which way the numbers went — for now, that is all we have here.

One source, 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 4

    Cognitive 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
    Not in the abstract
    Which way it went
    No clear difference
    Likely range
    Not in the abstract
    Source’s own words
    no pooled anxiety estimate reported; the single-study exception is reported as a standardised effect size
    Who was studied
    Adult
    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
    1. Starts at High
    2. Risk of bias brought it down to Moderatethe abstract's own appraisal reports serious study limitationsReported in the abstract
    3. Imprecision brought it down to Lowthe abstract reports no confidence interval for the estimateNot in the abstract
    4. 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-reviewed & signed — an AI agent re-read this finding against the saved source and checked that the quote, the numbers, the units and the direction match it. No person read it. The owner authorised the agent to sign the batch with the owner's key, and every build rechecks that signature against these exact bytes.

    Read the abstract on PubMed

What is still missing from these readings

  • No number at all, only which way it went.
  • One gives no likely range, so how precise that number is is unknown.
  • One do not say how many people took part.
  • Amount taken — Not in the abstract.
  • For how long — 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

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.