Supplement analysis backed by scientific evidence · PT · ES · DE · FR

← All supplements
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.

View on iHerb Ships to 180+ countries · welcome discount for new customers

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.

How to take it

TimingTiming does not matter.
With food?With a meal containing fat, which improves resveratrol absorption.
Worth knowingBuy an extract standardized for trans-resveratrol rather than whole-root tincture — the emodin in whole root is what causes the loose stools.

Interactions

With medications

  • warfarin and other anticoagulants

    Resveratrol inhibits CYP2C9 and has mild antiplatelet activity, raising bleeding risk. avoid, or monitor INR closely with your prescriber

  • statins and other CYP3A4 substrates

    Resveratrol inhibits CYP3A4, raising drug blood levels. check with a pharmacist before combining

  • tamoxifen and other hormone therapies

    Resveratrol is weakly estrogenic and may oppose anti-estrogen treatment. avoid during breast cancer treatment

With other supplements

  • fish oil, ginkgo and other antiplatelet supplements

    Additive bleeding tendency. stop all of them two weeks before surgery

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

What is Japanese knotweed used for in supplements?

Japanese knotweed root is the main industrial source of resveratrol; typical extracts are standardized to 50% trans-resveratrol, so a 500 mg capsule delivers about 250 mg. Its efficacy therefore rests on resveratrol's human record, which is inconsistent, with roughly 1% oral bioavailability.

Does Japanese knotweed work for Lyme disease?

There is no clinical evidence: Japanese knotweed's use in Lyme protocols traces to a test-tube screen using a 1% extract, a concentration no oral dose can reach in the blood. No clinical trial of Japanese knotweed in Lyme disease exists.

Why does Japanese knotweed cause loose stools?

Whole-root Japanese knotweed contains emodin, a stimulant laxative anthraquinone that causes loose stools and cramping and has shown genotoxicity signals in some assays. Extracts standardized for trans-resveratrol are the more predictable choice.

Is Japanese knotweed safe with blood thinners?

Caution is needed: resveratrol from Japanese knotweed inhibits CYP2C9 and CYP3A4 and has mild antiplatelet activity, raising bleeding risk with warfarin and levels of statins. Resveratrol is also weakly estrogenic, so avoid it during tamoxifen or other breast cancer treatment.

Scientific references

Where to buy

Solaray, Vital Extracts, Resveratrol Japanese Knotweed, 60 VegCaps

View on iHerb

Ships to 180+ countries · welcome discount for new customers

Referral link — this site may earn a commission on purchases.

Related in Longevity & antioxidants