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Open WellbeingWhat the studies actually measured

Sleep

L-theanineand Sleep onset latency

Only one source here so far, and it measured lower sleep onset latency.

How sure anyone can be

Very low certainty, level 1 of 4

Any estimate here is very uncertain.

The numbers reported

One source’s range, drawn against its own line of no difference and scaled to its own numbers.

0.010.15 standardised effect size0.29

This range stays on one side of the no-difference line.

Bar the confidence interval — the range the true effect is likely to sit inNotch the number the source reportedLine where there would be no difference at all

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, 2025 · 10 studies pooled

    Very low certainty, level 1 of 4

    The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.

    Sleep Med Rev. 2025;81:102076. doi:10.1016/j.smrv.2025.102076. PMID:40056718.

    Number reported
    0.15 standardised effect size
    Which way it went
    Lower
    Likely range
    0.01 to 0.29
    Source’s own words
    standardised mean difference in subjective sleep onset latency
    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, 3 steps down: risk of bias, indirectness and imprecision
    1. Starts at High
    2. 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
    3. Indirectness brought it down to Lowthe outcome measured is a proxy for the target outcomeReported in the abstract
    4. Imprecision brought it down to Very lowthe abstract does not state how many participants were pooledNot in the abstract
    5. Ends at Very low3 steps down.
    Inconsistency
    No high disagreement reported between the 10 studies it pooled

    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

  • 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.