Japanese Knotweed

Also called Polygonum cuspidatum, Reynoutria japonica, Fallopia japonica, Hu Zhang.

Best grade D across 4 graded outcomes Botanical Last checked Oct 21, 2026

The short answer

From 14 sources

Japanese knotweed root extract is the usual source of supplement resveratrol and also contains emodin. Human evidence is thin: two 20-person trials of a 200 mg extract (40 mg resveratrol) lowered inflammation markers, and a small Gulf War Illness trial was positive. Respiratory-infection results come from multi-herb formulas. Label resveratrol content is often inaccurate.

Every graded outcome on this page

4 rows · line = participants

Grade DSymptom improvement in acute respiratory infections (multi-herb formulas)Respiratory infectionsn 1,013
Grade DSymptom severity in Gulf War IllnessGulf War Illnessn 21
Grade DInflammation and oxidative-stress markers in healthy adultsInflammation markersn 20
Grade DInflammation markers in professional basketball playersInflammation markersn 20

Key facts

What it is: The root of Polygonum cuspidatum (also Reynoutria or Fallopia japonica), rich in resveratrol and its glycosides⁴
Studied extract: 200 mg/day standardized to 20% trans-resveratrol (40 mg resveratrol) in two 6-week trials of 20 people each^1,2
Other active compound: Emodin, an anthraquinone that a 2016 review links to liver, kidney and reproductive toxicity, particularly at high doses and with long-term use⁷
Label accuracy: In 20 resveratrol supplements, 95% differed from the declared amount; in another test of 14 brands, only 5 were within GMP range^8,9
EU limit: EU novel-food conditions cap trans-resveratrol in supplements at 150 mg/day⁸
Liver safety: LiverTox rates resveratrol an unlikely cause of liver injury (score E); a 2026 report described probable liver injury from a Huzhang (knotweed root) formula, linked by the authors to emodin^12,14

What it is

Japanese knotweed root is the main commercial source of resveratrol and also contains emodin, an anthraquinone.

How it works

Proposed

The extract’s resveratrol is proposed to dampen inflammatory signalling (for example NF-κB) and reactive oxygen species in white blood cells, as measured in one small trial. Emodin, another root compound, acts as an anthraquinone; its pharmacology and toxicity come largely from animal and cell studies. Lab tests found activity against the Lyme bacterium, but there are no clinical trials.^1,7,10

Forms, side by side

2 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.

Japanese Knotweed forms compared

2 forms

Japanese Knotweed forms compared: 2 forms by 3 attributes. Empty cells are labelled No data yet, or Not graded in the evidence row.
2 forms	Root extract standardized to trans-resveratrol	Whole-root extract or powder (contains emodin)
Absorption in people	Resveratrol itself peaked in blood 0.8–1.5 h after a dose, with low plasma levels even at 150 mg six times a day and higher bioavailability after morning doses.⁵	Emodin had poor oral bioavailability in rats because of extensive glucuronidation; no human data cited.⁷
GI tolerance	No adverse effects were reported in the abstracts of the two 6-week extract trials.^1,2	Emodin is linked to liver, kidney and reproductive toxicity, particularly at high doses and with long-term use.⁷
Studied for	Inflammation-marker trials (200 mg/day extract, 40 mg resveratrol)	Ingredient of multi-herb formulas in respiratory-infection trials

Root extract standardized to trans-resveratrol
Absorption in people
Resveratrol itself peaked in blood 0.8–1.5 h after a dose, with low plasma levels even at 150 mg six times a day and higher bioavailability after morning doses.⁵
GI tolerance
No adverse effects were reported in the abstracts of the two 6-week extract trials.^1,2
Studied for
Inflammation-marker trials (200 mg/day extract, 40 mg resveratrol)
Whole-root extract or powder (contains emodin)
Absorption in people
Emodin had poor oral bioavailability in rats because of extensive glucuronidation; no human data cited.⁷
GI tolerance
Emodin is linked to liver, kidney and reproductive toxicity, particularly at high doses and with long-term use.⁷
Studied for
Ingredient of multi-herb formulas in respiratory-infection trials

What the human research says

Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.

Trial map

4 graded outcomes, largest study first

All 4 graded outcomes found an improvement. The largest, a 2022 systematic review of 1,013 people on symptom improvement in acute respiratory infections (multi-herb formulas), found an improvement.

By sizeTable

1Symptom improvement in acute respiratory infections (multi-herb formulas)

Improved · Grade D · Systematic review, 1,013 people, 2022

Adults and children with acute respiratory tract infections (7 trials pooled for this outcome)

Dose, result and source

Every graded outcome on this page, largest study first
Outcome	Found	People	Study	Who was studied
Symptom improvement in acute respiratory infections (multi-herb formulas)	Improved	1,013	Grade D · Systematic review, 2022	Adults and children with acute respiratory tract infections (7 trials pooled for this outcome)
Symptom severity in Gulf War Illness	Improved	21	Grade D · Crossover RCT, 2021	Male veterans with Gulf War Illness (USA)
Inflammation markers in professional basketball players	Improved	20	Grade D · RCT, 2013	Healthy male professional basketball players
Inflammation and oxidative-stress markers in healthy adults	Improved	20	Grade D · RCT, 2010	Normal-weight healthy adults

Every graded row

4 rows

Form tested

Showing 4 of 4 outcomes. Human trials only.

Grade DSymptom improvement in acute respiratory infections (multi-herb formulas)Respiratory infectionsImprovedSystematic review · 7 studies
n 1,013 · 2022

Improved Formulas containing the herb raised the symptom-improvement rate (risk ratio 1.14, 95% CI 1.09–1.20), shortened fever and did not increase adverse events.

Design: Systematic review, 7 studies, n = 1,013, 2022
Population: Adults and children with acute respiratory tract infections (7 trials pooled for this outcome)
Form: Reynoutria japonica as one ingredient of herbal mixtures, mostly given alongside antibiotics
Dose: Varied by formula (not stated in the abstract)
Duration: Varied
Source: Reference 4 · PubMed 35281919 (opens PubMed)

Grade DSymptom severity in Gulf War IllnessGulf War IllnessImprovedCrossover RCT
n 21 · 2021

Improved Symptom severity fell more than with placebo at both the lower (p=0.035) and higher (p=0.004) dose.

Design: Crossover RCT, n = 21, 2021
Population: Male veterans with Gulf War Illness (USA)
Form: Resveratrol from Polygonum cuspidatum
Dose: Lower and higher doses (amounts not stated in the abstract)
Duration: 1 month per dose level, after 1 month of placebo
Source: Reference 3 · PubMed 33802381 (opens PubMed)

Grade DInflammation and oxidative-stress markers in healthy adultsInflammation markersImprovedRCT
n 20 · 2010

Improved Reactive oxygen species from white blood cells, NF-κB binding and plasma TNF-α, IL-6 and C-reactive protein fell compared with baseline and placebo; the placebo group showed no change.

Design: RCT, n = 20, 2010
Population: Normal-weight healthy adults
Form: Polygonum cuspidatum extract containing resveratrol
Dose: Extract providing 40 mg resveratrol/day
Duration: 6 weeks
Source: Reference 1 · PubMed 20534755 (opens PubMed)

Grade DInflammation markers in professional basketball playersInflammation markersImprovedRCT
n 20 · 2013

Improved Plasma TNF-α and IL-6 fell after 6 weeks of extract, with no change in the placebo group.

Design: RCT, n = 20, 2013
Population: Healthy male professional basketball players
Form: Polygonum cuspidatum extract standardized to 20% trans-resveratrol
Dose: 200 mg/day (40 mg trans-resveratrol)
Duration: 6 weeks
Source: Reference 2 · PubMed 23717757 (opens PubMed)

What the numbers add up to

Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.

Knotweed trials used modest resveratrol doses

Both extract trials delivered about 40 mg of resveratrol a day, far below the 1 g/day that altered drug-metabolising enzymes in volunteers.^2,6

Markers, not outcomes

The positive knotweed trials measured inflammation markers or symptom scores in 20–21 people; none measured hard clinical outcomes.^1,2,3

Studied doses

Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.

Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.

Doses studied in human trials

Doses studied in human trials ranged from 200 mg/day of Polygonum cuspidatum extract (about 40 mg of resveratrol) for 6 weeks in two small trials; a Gulf War Illness study tested two unstated doses for 1 month each. These are research doses, not recommendations.^1,2,3

Interactions and safety

Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.

What Japanese Knotweed meets

3 cited rows

Medicines 3

Japanese Knotweed3 medicines · 0 supplements

Supplements and foods 0

No supplement rows in our sources.

Measured in a human study
Reference summary

Interactions

3 agents

Published interactions, grouped by kind
Agent	What the source says	Evidence
Medicines3
Drugs cleared by CYP3A4, CYP2D6 or CYP2C9e.g. buspirone, dextromethorphan and losartan (the probe drugs used)	In 42 healthy adults, 1 g/day of pure resveratrol for 4 weeks inhibited these enzymes and induced CYP1A2; the authors warn this could raise adverse drug reactions. That dose is about 25 times the resveratrol in the studied knotweed extract.^6,1	PK study
Blood thinners, blood-pressure and diabetes medicines	A 2023 review of herbs used for Lyme symptoms, including Japanese knotweed, warns that many have drug interactions and additive effects that could raise the risk of bleeding, low blood pressure and low blood sugar. LiverTox also lists possible interactions between resveratrol and anticoagulants.^10,12	Review
Estrogens	LiverTox lists possible supplement–drug interactions between resveratrol and estrogens; it gives no case details or size of effect.¹²	Review

Check with what you take

Kept on this device only

Add what you take. We list every interaction our evidence profiles cite between Japanese Knotweed and your picks, and between your picks.

Add a supplement or medicine

Most cited:

Add a supplement or medicine you take to check it against Japanese Knotweed.

Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.

Who should be careful

5 groups

Pregnancy and breastfeeding: No pregnancy data: the trials cited here enrolled non-pregnant adults. For breastfeeding, LactMed (resveratrol) found no data on transfer into milk or on infant safety, and says supplements usually contain hundreds of times the amounts in food, so their safety while nursing cannot be assured.^11,1,2,3
People on prescription medicines: High-dose resveratrol changed the activity of several drug-metabolising enzymes in healthy volunteers.⁶
Long-term high intake of whole-root products: Emodin, present in the root, is linked to liver, kidney and reproductive toxicity, particularly at high doses and with long-term use, according to a 2016 review.⁷
Liver: LiverTox gives resveratrol likelihood score E (unlikely cause of clinically apparent liver injury); doses of 1.5–3 g/day only raised liver enzymes slightly. Whole-root products also contain emodin: a 2026 report described probable liver injury (RUCAM score 6) in a 72-year-old after 14 days of a Huzhang-containing formula, which resolved with treatment.^12,7,14
Mix-up with fo-ti (He Shou Wu): Polygonum multiflorum, sold as fo-ti, He Shou Wu or "Chinese knotweed", is a different plant. LiverTox gives it likelihood score A (a well-established cause of liver injury, occasionally fatal), so check the Latin name: Japanese knotweed is Polygonum cuspidatum (Reynoutria or Fallopia japonica).¹³

How the body handles knotweed resveratrol

3 notes

Resveratrol is absorbed quickly and cleared quickly.

Half-life: Trans-resveratrol half-life was 1–3 h after single doses and 2–5 h after repeated dosing, with large differences between people.⁵
Blood levels: Even at 150 mg six times a day, peak plasma resveratrol averaged 63.8 ng/mL, which the authors describe as relatively low.⁵
Legal status: EU: novel-food conditions for food supplements with trans-resveratrol set a maximum of 150 mg/day; a quarter of 20 products tested in Slovenia exceeded it per unit.⁸

How to read the label

What to check on the Supplement Facts panel.

How to read the label

4 checks

Extract weight vs resveratrol

The studied extract was 200 mg standardized to 20% trans-resveratrol, so check the resveratrol amount, not just the extract weight.²

Expect label errors

95% of 20 tested resveratrol supplements differed from the label, and 2 of 14 brands in another study had no detectable resveratrol.^8,9

Label dose vs studied dose

The knotweed trials used about 40 mg/day of resveratrol, while the EU allows up to 150 mg/day in supplements; a quarter of tested products exceeded that cap per unit.^1,8

Same plant, different names

Polygonum cuspidatum, Reynoutria japonica and Fallopia japonica all refer to Japanese knotweed. Polygonum multiflorum (fo-ti, "Chinese knotweed") is a different herb with a well-established liver-injury risk.^4,13

Have the bottle? Photograph its Supplement Facts panel and see each line, japanese knotweed included, beside the doses and forms the trials used in Label X-Ray.

Frequently asked questions

Short answers to common questions; the numbers link to the sources below.

Common questions

7 answers

Does Japanese knotweed help with Lyme disease?

Lab tests found activity against the Lyme bacterium, but a 2023 review found no clinical trials.¹⁰

Does Japanese knotweed help colds or respiratory infections?

Only as part of multi-herb formulas, mostly with antibiotics; the herb’s own effect is unknown.⁴

Is Japanese knotweed safe?

Short trials reported no problems in their abstracts, and LiverTox rates resveratrol an unlikely cause of liver injury. But the whole root contains emodin, with a 2026 case of probable liver injury from a Huzhang formula, and high-dose resveratrol changed drug-metabolising enzymes.^1,2,12,14,6

Is Japanese knotweed the same as resveratrol?

No. The root is the main commercial source of resveratrol, but it also contains other compounds such as emodin.^4,7

Is Japanese knotweed the same as fo-ti or He Shou Wu?

No. Fo-ti (He Shou Wu) is Polygonum multiflorum, sometimes sold as "Chinese knotweed". LiverTox rates it a well-established cause of liver injury (score A), whereas resveratrol, the main compound sought from Japanese knotweed, scores E (unlikely).^13,12

What does Japanese knotweed do in studies?

In two 20-person trials, 200 mg/day of extract (40 mg resveratrol) for 6 weeks lowered inflammation markers. Clinical benefits have not been shown.^1,2

How much resveratrol is in knotweed supplements?

It varies, and labels are often wrong: 95% of 20 tested products differed from the stated amount.⁸

Sources

14 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.

Sources cited on this page

14 sources

1An antiinflammatory and reactive oxygen species suppressive effects of an extract of Polygonum cuspidatum containing resveratrol.RCT J Clin Endocrinol Metab, 2010 · PMID 20534755
2Effects of polygonum cuspidatum containing resveratrol on inflammation in male professional basketball players.RCT Int J Prev Med, 2013 · PMID 23717757
3A Placebo-Controlled, Pseudo-Randomized, Crossover Trial of Botanical Agents for Gulf War Illness: Resveratrol (Polygonum cuspidatum), Luteolin, and Fisetin (Rhus succedanea).Crossover RCT Int J Environ Res Public Health, 2021 · PMID 33802381
4Reynoutria japonica Houtt for Acute Respiratory Tract Infections in Adults and Children: A Systematic Review.Systematic review Front Pharmacol, 2022 · PMID 35281919
5Pharmacokinetic and safety profile of trans-resveratrol in a rising multiple-dose study in healthy volunteers.PK study Mol Nutr Food Res, 2009 · PMID 19194969
6Resveratrol modulates drug- and carcinogen-metabolizing enzymes in a healthy volunteer study.PK study Cancer Prev Res (Phila), 2010 · PMID 20716633
7Emodin: A Review of its Pharmacology, Toxicity and Pharmacokinetics.Review Phytother Res, 2016 · PMID 27188216
8Resveratrol Food Supplement Products and the Challenges of Accurate Label Information to Ensure Food Safety for Consumers.Observational Nutrients, 2023 · PMID 36678345
9trans-Resveratrol in nutraceuticals: issues in retail quality and effectiveness.Observational Molecules, 2012 · PMID 23090020
10A Comprehensive Review of Herbal Supplements Used for Persistent Symptoms Attributed to Lyme Disease.Review Integr Med (Encinitas), 2023 · PMID 37101730
11ResveratrolDatabase LactMed (NCBI Bookshelf), 2021 · ncbi.nlm.nih.gov
12ResveratrolDatabase LiverTox (NCBI Bookshelf), 2024 · ncbi.nlm.nih.gov
13Polygonum MultiflorumDatabase LiverTox (NCBI Bookshelf), 2020 · ncbi.nlm.nih.gov
14A case report and a literature review of drug-induced liver injury caused by Huzhang according to the updated RUCAM.Review Medicine (Baltimore), 2026 · PMID 41630279

What changed

Every dated change to this page: what changed, who made it and why.

Change log

3 entries

Dated changes to this page
Date	Change	Who and why
Oct 21, 2026key facts, interactions, who should avoid, label guide, FAQ, questions, related	Added the LactMed resveratrol entry to the breastfeeding note (no milk or infant data; supplement doses not assured safe), a liver note with the LiverTox resveratrol score (E, unlikely) and a 2026 probable liver-injury case from a Huzhang (knotweed root) formula, and a warning not to confuse the herb with Polygonum multiflorum (fo-ti, LiverTox score A). Added LiverTox's possible resveratrol interactions with anticoagulants and estrogens, a FAQ on fo-ti, page questions and the healthy-aging goal hub. PubMed search for 2023–2026 meta-analyses and RCTs (Polygonum cuspidatum, Reynoutria japonica, Japanese knotweed, Huzhang) found only multi-ingredient products (a 2024 Huzhang granule gout trial, polyphenol blends in 2019 and 2026), so no evidence row was added and the newest row stays 2022. NCCIH and MedlinePlus have no knotweed or resveratrol page.	Writer: Kymata Health EditorialTrigger: A–Z audit against docs/supplements/AUDIT-STANDARD.md
Oct 14, 2026all	Adversarial review pass: every evidence row, key fact, interaction, safety note and FAQ re-read against its PubMed abstract or source page, and every number machine-checked against the cited source text. Retraction, expression-of-concern and withdrawn checks on all PMIDs: none flagged. Fixes: emodin toxicity attributed to the 2016 review without an unsupported "mostly animal" qualifier; an unsourced claim about typical label amounts removed; countries not stated in abstracts removed.	Writer: Kymata Health EditorialTrigger: review
Oct 14, 2026all	Initial editorial evidence review (first draft). Every PMID checked against NCBI E-utilities esummary (titles and years taken from the record) and the abstract read for each cited row. Studied doses are reported as research doses, not dosing advice.	Writer: Kymata Health EditorialTrigger: new page

Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.

Japanese Knotweed

Medicines 3

Supplements and foods 0

Drugs cleared by CYP3A4, CYP2D6 or CYP2C9

Blood thinners, blood-pressure and diabetes medicines

Estrogens