Supplement analysis backed by scientific evidence · PT

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Limited evidenceLongevity & antioxidants

Japanese Knotweed

This is where almost all commercial resveratrol comes from, so its longevity claims inherit resveratrol's unimpressive human record. Its separate reputation as a Lyme herb rests entirely on a test-tube screen at concentrations unreachable in the body.

What the science says

  • It is the source material for most 'resveratrol' supplements Moderate evidence

    Polygonum cuspidatum (Reynoutria japonica) root is the standard industrial source of trans-resveratrol, and typical products are root extracts standardised to 50% trans-resveratrol — so a 500 mg knotweed capsule delivers about 250 mg resveratrol. That means the human efficacy question is really the resveratrol question, and oral resveratrol has roughly 1% bioavailability with inconsistent results across metabolic and cardiovascular trials.

  • Lyme disease and 'persistent Lyme' protocols Limited evidence

    Knotweed's place in Lyme protocols traces largely to a 2020 Johns Hopkins in-vitro screen in which a 1% P. cuspidatum extract showed good activity against stationary-phase Borrelia burgdorferi. One percent means roughly 10,000 mg/L in a culture dish — a concentration no oral dose can produce in human plasma. No clinical trial of knotweed in Lyme disease exists, and the authors framed the work as a screening step, not a treatment recommendation.

  • Whole-root products carry emodin as well as resveratrol Moderate evidence

    Reviews of the genus document that P. cuspidatum root contains anthraquinones, principally emodin, alongside resveratrol and polydatin. Emodin is a stimulant laxative and has produced positive signals in some genotoxicity assays. Unstandardised whole-root powders and tinctures deliver an uncontrolled emodin dose; extracts standardised for trans-resveratrol are the more predictable choice.

Dosage & safety

Studied doseStandardised extracts: 250-500 mg of 50% trans-resveratrol root extract daily, supplying 125-250 mg resveratrol. Lyme protocols commonly recommend 1-4 mL of tincture two to three times daily escalating over weeks — a regimen with no clinical testing behind it. Resveratrol itself has been tested at 1-5 g/day in short trials, where GI side effects become common.
SafetyEmodin in whole-root products causes loose stools and cramping and carries genotoxicity signals in some assays; long-term anthraquinone use is not advisable. Resveratrol above roughly 1 g/day commonly causes nausea and diarrhoea and inhibits CYP3A4 and CYP2C9 — a real interaction risk with warfarin, statins and many other drugs — and it has mild antiplatelet activity, so stop before surgery. Resveratrol is weakly estrogenic; caution with hormone-sensitive cancers and with tamoxifen. Avoid in pregnancy and breastfeeding. Not banned in sport.

Scientific references

Where to buy

Solaray, Vital Extracts, Resveratrol Japanese Knotweed, 60 VegCaps

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