Cross-referencing clinical data
A pairing appears on this page only when a trial gave both ingredients together and measured the result. Holly has none that clears that bar.
Stitching two separate single-ingredient studies into a pairing is the one thing this engine will not do. When a study of the combination itself holds up at source, it lands here with its citation.
No invented synergy. Where actives were studied on their own rather than together, the record shows each on its own evidence, never a combined effect no trial measured.
Research strength. Research strength says how much work stands behind the combination. It is never a product score.
Independent record. Every finding is cited to a named trial, dated, and never written by the brand.
20 pairings are live across the library today. Checked 20 July 2026.
No study gave these as a pair, so they are not in the card above. But the reason they belong together is settled biochemistry, not a guess, so it is worth knowing.
Caffeine-bearing hollies deliver methylxanthines in the leaf, so adding isolated caffeine on top stacks the same compound rather than adding a second mechanism. Anyone counting a daily caffeine total needs to count the holly leaf serving in it. This does not apply to the non-caffeine ornamental hollies, which is exactly why the species on the label matters.
Theanine is routinely paired with caffeine sources to shift the subjective character of the stimulation, and the pairing has been studied with caffeine itself. Caffeine-bearing holly leaf is a caffeine source, so the same logic carries. Note that unlike tea, Ilex leaf does not supply theanine of its own, so it has to be added.
Holly leaf infusions carry a substantial polyphenol load, chlorogenic acids in particular, which bind non-heme iron and lower its absorption. The handling is the same as for tea or coffee: put distance between the drink and the iron dose. The effect scales with how strong the infusion is.
Ascorbate keeps iron in the ferrous state and partly rescues absorption from polyphenol binding. It softens the interaction between a polyphenol-heavy leaf infusion and an iron dose rather than removing it. Useful in a formula, not a substitute for spacing them.
Caffeine raises urinary calcium loss somewhat, so a high daily intake of caffeine-bearing holly leaf sits against calcium balance rather than with it. The size of the effect is small at ordinary intakes and matters most when calcium intake is already low. Again, this applies only to the caffeine-containing Ilex species.
Stacking a caffeine-bearing holly with green tea extract doubles up on both the methylxanthine and the polyphenol side. That matters for the caffeine total and for the combined tannin burden on iron and protein binding. It is duplication rather than complementarity.
Nothing specific on file for Holly. Match the label to the daily amount above, and tell your doctor what you take.
Not medical advice. Show the label to your pharmacist.These are the studies our verdict leans on, chosen from the 2 we read for Holly. The full linked list is below.
2 sources behind our Holly verdict: peer-reviewed studies and registered clinical trials. Every one links straight to PubMed, the journal, or ClinicalTrials.gov. Read them yourself.
Evidence surfaced via Semantic Scholar (Allen Institute for AI) and ClinicalTrials.gov. Ranked by study type and citation weight, not cherry-picked.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.