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Open WellbeingWhat the studies actually measured

Hormones, thyroid and fertility

Tongkat Aliand Total testosterone

Both sources here measured higher total testosterone.

How sure anyone can be

Low certainty, level 2 of 4

Further 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.

0.5651.352 standardised effect size2.138

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

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, 2024

    Low certainty, level 2 of 4

    Do "testosterone boosters" really increase serum total testosterone? A systematic review.

    Int J Impot Res. 2024;36(4):348-364. doi:10.1038/s41443-023-00763-9. PMID:37697053.

    Number reported
    Not in the abstract
    Which way it went
    Higher
    Likely range
    Not in the abstract
    Source’s own words
    no pooled total-testosterone estimate printed for Eurycoma longifolia
    Who was studied
    Adult male
    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 reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot 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.

    Source saved; quote checked byte-for-byte against it by software; no signature.

    Read the abstract on PubMed

  • Systematic review, 2022 · 5 studies pooled

    Low certainty, level 2 of 4

    Eurycoma longifolia (Jack) Improves Serum Total Testosterone in Men: A Systematic Review and Meta-Analysis of Clinical Trials.

    Medicina (Kaunas). 2022;58(8). doi:10.3390/medicina58081047. PMID:36013514.

    Number reported
    1.352 standardised effect size
    Which way it went
    Higher
    Likely range
    0.565 to 2.138
    Source’s own words
    standardised mean difference in serum total testosterone vs control
    Who was studied
    Adult male
    Compared with
    placebo or control
    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 reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot in the abstract
    3. Imprecision brought it down to Lowthe abstract does not state how many participants were pooledNot in the abstract
    4. Ends at Low2 steps down.
    Checked, nothing to step it down for
    indirectness
    Inconsistency
    No high disagreement reported between the 5 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 give no number at all, only which way it went.
  • One gives no likely range, so how precise that number is is unknown.
  • Two 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 Tongkat Ali

Five of the 13 things on our list for Tongkat Ali have no reading here yet:

  • DHEA-sulfate
  • Grip Strength
  • Serum cortisol (morning)
  • Sperm concentration
  • Total sperm motility

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.