Knotweed

Knotweed (Fallopia japonica / Polygonum cuspidatum): A Comprehensive Reference

1. Identity: Botanical Classification, Nomenclature, and Common Forms

1.1 Botanical and Chemical Identity

Japanese Knotweed is scientifically known as Fallopia japonica and is often referred to by its synonyms Reynoutria japonica or Polygonum cuspidatum. It is a robust, perennial herbaceous plant native to the volcanic regions of East Asia, including Japan, China, and Korea. It is a member of the Polygonaceae family (buckwheat). The taxonomy of this plant has been subject to revision: all three names—Fallopia japonica, Reynoutria japonica, and Polygonum cuspidatum—appear in the scientific literature and refer to the same species.

The English names for Japanese knotweed include Huzhang, fleeceflower, Hancock's curse, elephant ears, donkey rhubarb, sally rhubarb, American bamboo, Japanese bamboo, and Mexican bamboo (though it is not actually a bamboo). It is a large perennial plant, native to eastern Asia in Japan, China, and Korea; this species now grows in vast areas throughout the northeastern USA into Canada and Europe, and was introduced from Japan into the UK in the 19th century.

It is a large herbaceous perennial plant, approximately 2 m high. The stems are numerous, erect, and hollow with distinct raised nodes, often with red or purple spots. The leaves are deciduous; the petioles are 1–2 cm long and papillate. The leaf blades are ovate or broadly elliptic, 5–12 × 4–9 cm in size, and subleathery.

1.2 Medicinally Used Plant Parts

The rhizome (root) is the primary medicinal part, harvested for its concentrated active constituents. Research has shown that the root contains a much higher level of resveratrol than the stem and leaf, and it is accumulated at its highest level in October. A 3-year field study observed that the concentrations of different antioxidants, namely trans-resveratrol, resveratroloside, polydatin, and emodin, decreased during the growth period in the aboveground biomass; simultaneously, the concentrations in the belowground biomass increased when the plant started to accumulate important storage substances for winter rest.

1.3 Common Preparations and Dosage Forms

Knotweed is commercially available in a variety of forms. In Western supplement markets, standardized root extracts are the most prevalent format, typically standardized to a defined percentage of trans-resveratrol. P. cuspidatum extracts, particularly for resveratrol, are widely used in dietary supplements, but they lack formal GRAS (Generally Recognized as Safe) status from the US FDA. The rhizome and root of the plant (Polygoni cuspidati rhizoma et radix) was included in the European Pharmacopoeia in 2017. The dried root is officially listed in the Pharmacopoeia of the People's Republic of China under the name "Hu Zhang."

Common preparation forms include: encapsulated dry root powder; standardized liquid extracts and tinctures; standardized capsule or tablet extracts (quantified by resveratrol content); and decocted root preparations in traditional settings. In the UK, trans-resveratrol is authorised as a novel food with a maximum daily intake of 150 mg for adults; it is regulated as a food supplement, not a medicine.

2. Traditional and Historical Use

2.1 Traditional Chinese Medicine (TCM)

Polygonum cuspidatum has been one of the most widely used herbs in TCM for thousands of years, with the earliest record found in the Mingyi Bielu, and was traditionally used to promote blood circulation, decrease humidity, remove stasis, and alleviate pain. In TCM, Polygonum cuspidatum is known as Hu Zhang and has been used for centuries as a blood-invigorating, heat-clearing, and detoxifying herb. TCM considers Hu Zhang to be bitter and slightly cold, entering the liver, gallbladder, and lung meridians. It is often used to disperse blood stasis, eliminate toxins, and resolve damp-heat, particularly in liver and skin disorders.

From the perspective of TCM theory, Hu Zhang is used to remove jaundice and clear heat-toxin so as to promote blood circulation, dispel stasis, expel wind and dampness, dissipate phlegm, and suppress cough. The therapeutic uses of Hu Zhang-containing TCM prescriptions or formulations include treating cough, hepatitis, jaundice, amenorrhea, leucorrhea, arthralgia, burns, and snake bites. Hu Zhang is frequently used as a hepatoprotective and cholagogic drug in TCM.

2.2 Japanese and Korean Traditional Medicine

In Japanese herbal medicine (Kampo), knotweed preparations were used to stimulate circulation and treat infections. The root of P. cuspidatum has been used in Korea to maintain oral hygiene and to control oral diseases, particularly biofilm-related diseases. Folk remedies throughout Korea and China also included treatment of snake bites, burns, skin ulcers, and fevers.

2.3 Introduction to the West and Emergence in Modern Supplements

With the isolation of resveratrol in the late 20th century, Polygonum cuspidatum gained recognition in Western integrative and functional medicine, especially for cardiovascular and anti-aging support. Japanese knotweed is considered an invasive pest and is a commercial source of resveratrol. Today it represents one of the primary botanical raw materials from which commercial resveratrol is extracted globally.

3. Key Constituents and Active Compounds

3.1 Full Phytochemical Profile

F. japonica is known to produce a series of bioactive secondary metabolites, including anthraquinones, stilbenes, tannins, lignans, anthocyanins, phenethyl alcohols, sterols, and essential oils. More specifically, the phytochemical composition of knotweed, particularly its rhizomes, includes important amounts of anthraquinones (emodin, citreorosein, fallacinol, physcion, etc.), flavonoids (rutin, apigenin, quercetin, quercitrin, isoquercitrin, hyperoside, reynoutrin, and kaempferol), and most importantly, stilbenes (resveratrol and polydatin), coumarins, lignans, essential oils, and other compounds.

Stilbenes including resveratrol, polydatin, and anthraquinones such as emodin and its glycoside are the major compounds in Hu Zhang. Hu Zhang also contains flavonoids such as quercetin and (+)-catechin.

3.2 Resveratrol (trans-3,4′,5-trihydroxystilbene)

Resveratrol (3,4′,5-trihydroxystilbene; molecular weight 228.2 g/mol) is a naturally occurring polyphenol that is present in various fruits and vegetables in significant levels. It is classified as a phytoalexin, meaning it is produced by plants in response to stress, injury, or infection. Japanese knotweed is one of the most concentrated botanical sources of resveratrol, often used as a more sustainable alternative to grape-derived resveratrol in supplements.

Research has revealed that the chemical composition of the roots of different species of Fallopia (F. japonica, F. bohemica, and F. sachalinensis) contained a higher amount of piceid and resveratrol. Comparing two Fallopia species, Lachowicz and Oszmianski (2019) reported that the leaves were a source of polymeric procyanidins, flavones, flavonols, phenolic acids, oleanolic and ursolic acids, while the roots contain flavan-3-ols and stilbenes, resveratrol being the most dominant.

3.3 Polydatin (Resveratrol-3-O-β-D-Glucoside / Piceid)

Polydatin is the glycosylated form of resveratrol and is found alongside it in the root and rhizome. Resveratrol-glucosides (e.g., piceid) can be split into glucose and resveratrol, which increases the resveratrol levels. The anthraquinone emodin modulates AMPK/mTOR and Nrf2/HO-1 pathways, conferring hepatoprotective and antioxidant effects, while polydatin (resveratrol-3-O-β-D-glucoside) enhances bioavailability and activates SIRT1 to improve mitochondrial function. The ratio between trans-resveratrol and its glycosylated form, polydatin, varies not only by location but also by the time period of sample collection.

3.4 Emodin (1,3,8-trihydroxy-6-methylanthraquinone)

Emodin is a biologically active, naturally occurring anthraquinone derivative (1,3,8-trihydroxy-6-methylanthraquinone) that is produced by lichens, fungi, and higher plants, and possesses purgative, anti-inflammatory, and anticancer effects. Emodin is a natural anthraquinone derivative that occurs in many widely used Chinese medicinal herbs, such as Rheum palmatum, Polygonum cuspidatum, and Polygonum multiflorum. Emodin has been used as a traditional Chinese medicine for over 2,000 years and is still present in various herbal preparations. Emodin is used in traditional Chinese herbal medicine as a quality-control index for F. japonica.

4. Established Mechanisms of Action

4.1 Anti-inflammatory Mechanisms

Japanese knotweed root is a rich source of trans-resveratrol, emodin, polydatin, and anthraquinones that inhibit NF-κB and STAT3 signaling pathways, delivering potent anti-inflammatory, hepatoprotective, and cardiovascular benefits confirmed across multiple pharmacological reviews. Resveratrol exhibits strong anti-inflammatory characteristics owing to its ability to modulate small molecules in multiple signaling pathways to suppress the secretion of inflammatory factors.

4.2 Antioxidant Mechanisms

The compound resveratrol can neutralize reactive oxygen species (free radicals) and may help protect cells from oxidative stress, a process implicated in numerous chronic diseases and aging. The hydroxyl groups of resveratrol enable the molecule to scavenge free radicals, chelate metals, and interact with macromolecules, thus contributing to its antioxidative, antimicrobial, and health-promoting properties.

4.3 Sirtuin (SIRT1) Activation and Metabolic Pathways

The neuroprotective effects of resveratrol are mediated through the activation of sirtuins (SIRT1), inhibition of Aβ aggregation, modulation of Tau protein phosphorylation, and the attenuation of oxidative stress and inflammatory responses. Resveratrol also enhances mitochondrial function and promotes autophagy, which are important processes for maintaining neuronal health. The activation of SIRT1, a NAD⁺-dependent deacetylase, is considered central to several of resveratrol's proposed anti-aging and metabolic effects.

4.4 Anticancer Molecular Mechanisms

Resveratrol (a stilbene) and emodin (an anthraquinone) are the major active ingredients of F. japonica. The anticancer activity of both compounds has various molecular modes of action and mechanisms through their ability to modulate proliferation, apoptosis, cell cycle, growth factors, protein kinase C (PKC), NF-kappa B (NF-κB), and mitogen-activated protein kinase (MAPK) signaling cascades.

Emodin shows cytotoxicity and inhibition of precursor incorporation into DNA and RNA activities, which does not allow expression of genetic information in certain cell lines, in which it has been shown to be an antineoplastic agent. Like resveratrol, emodin is a strong inhibitor of protein tyrosine kinase.

4.5 Hepatoprotective Mechanisms

Emodin modulates AMPK/mTOR and Nrf2/HO-1 pathways, conferring hepatoprotective and antioxidant effects. A meta-analysis incorporating 28 studies with 537 rodents confirmed emodin's dual effects on liver injury. Controlled doses and durations of emodin significantly reduced aspartate aminotransferase (AST), ALT, and alkaline phosphatase (ALP) levels, primarily by inhibiting cytochrome P450 2E1 (CYP2E1) expression and activating the farnesoid X receptor/bile salt export pump (FXR/BSEP) pathway.

4.6 Cardiovascular Mechanisms

Laboratory research indicates resveratrol may influence endothelial function—the health of blood vessel linings—and has been investigated for effects on lipid profiles and blood pressure regulation. These compounds have been identified as responsible for some of the herb's key medicinal actions including tonic action on microcirculation, myocardial protective effects, anti-atherosclerotic activity, and antioxidant activity.

5. Scientific Evidence by Area of Use

5.1 Cardiovascular Health

The herb's effects on hypertension, hyperlipidemia, and cardiovascular and neurodegenerative diseases have been intensively investigated, both experimentally and clinically. Some observational and preliminary clinical studies have suggested potential cardiovascular benefits. However, large-scale clinical trials demonstrating definitive cardiovascular benefits in humans remain limited, and clinical regulatory bodies such as NICE do not recommend resveratrol for cardiovascular disease prevention or treatment.

In a 2014 randomized human clinical trial, a combination of Japanese knotweed extract and hawthorn extract was found to inhibit atherosclerosis as effectively as a statin medication. The authors suggested this effect was due to the herb's anti-inflammatory actions and ability to reduce tissue damage. However, this study used a combination formula rather than knotweed as a single herb, limiting attribution of effect.

Evidence strength: Preliminary. Predominantly preclinical (in vitro and animal model) data; a small number of human trials exist, but most involve resveratrol as an isolated compound rather than the whole knotweed extract. No large-scale RCTs specific to knotweed extracts and cardiovascular outcomes have been completed.

5.2 Anti-inflammatory Activity

A randomized, controlled trial studied athletic men and Japanese knotweed extract's effect on inflammation. Those who took 200 mg of Japanese knotweed daily (which contained a high dose of resveratrol) had significantly reduced markers of inflammation. A randomized, double-blind, cross-over trial studied resveratrol's anti-inflammatory and antioxidant effects on 50 adult smokers. Resveratrol significantly reduced the inflammatory marker C-reactive protein (CRP), decreased triglycerides, and increased overall antioxidant levels.

One clinical study used an oral extract of P. cuspidatum 200 mg containing resveratrol 40 mg over 6 weeks for anti-inflammatory effect.

Evidence strength: Weak to moderate. Some small RCTs suggest anti-inflammatory effects, but most are short-duration, small-sample studies. Effects of resveratrol from grape vs. knotweed sources are not always distinguished in the literature.

5.3 Neuroprotection and Alzheimer's Disease

Due to its antioxidant, anti-inflammatory, and neuroprotective properties, resveratrol has gained significant interest as a potential therapeutic agent for Alzheimer's disease (AD). Numerous preclinical studies have demonstrated the benefits of resveratrol in mitigating various aspects of Alzheimer's pathophysiology, including reduced Aβ aggregation, improved cognitive function, and enhanced synaptic integrity.

A meta-analysis comprised five trials involving 271 AD patients, of whom 139 received resveratrol treatment and 132 received placebo treatment. Compared with placebo therapy, resveratrol treatment resulted in a significant improvement in Alzheimer's Disease Cooperative Study—Activities of Daily Living (ADAS-ADL) scores.

Trans-resveratrol has demonstrated a neuroprotective effect in patients with mild to moderate AD, as evidenced by change scores on ADAS-cog, MMSE, ADCS-ADL, and NPI showing less deterioration in the treatment group compared to the control group, although none of the change scores reached statistical significance.

Evidence based on clinical studies is still insufficient, contradictory, and inconclusive, and further clinical trials are recommended to substantiate the neuroprotective effects of resveratrol and its likely mechanisms of action in the body. The neuroprotective effects of resveratrol are mainly short term, varying according to dose, dosage form, duration of treatment, pharmacokinetic and pharmacogenomic parameters, food, and drug interactions.

In neurodegenerative disease models (Alzheimer, Parkinson, and Huntington), resveratrol improves the pathological damage of neurons, increasing cell survival by inhibiting apoptosis, inflammation, and oxidative stress and thus improving cognitive impairment and the decline in motor function that accompany these diseases. These findings, however, remain predominantly in animal models.

Evidence strength: Preliminary. Preclinical data are substantial. Human trials are few, small, and have produced mixed or non-significant results. Resveratrol's poor oral bioavailability is a known pharmacokinetic limitation affecting translation of preclinical findings to clinical outcomes.

5.4 Metabolic Effects (Blood Sugar and Lipids)

Laboratory studies suggest resveratrol may influence insulin sensitivity and glucose metabolism, primarily through cellular mechanisms including sirtuin activation. Some small human trials have explored its potential role in metabolic syndrome and type 2 diabetes management, though results have been inconsistent and further research is needed.

Resveratrol can have a positive impact on both the prevention and treatment of chronic inflammatory diseases, such as obesity, neurodegeneration, diabetes, cardiovascular diseases, and cancers, among other conditions. However, these findings span a wide range of disease models and are not specific to knotweed extract as a whole-plant preparation.

Evidence strength: Preliminary. Mostly in vitro and animal evidence. Small, inconsistent human trials exist for isolated resveratrol; no large clinical trials of knotweed-specific extracts for metabolic endpoints have been published.

5.5 Antimicrobial Activity

Several studies confirmed that the bioactive compounds extracted from Japanese knotweed rhizomes possess curative properties against viral microorganisms. Liu et al. (2013) underlined the positive effect that the roots and rhizomes of P. cuspidatum have on treating the Coxsackievirus B4 (CVB4) infection. Specifically, emodin was explored through in vivo and in vitro assays, suggesting that it can lessen both the replication of Hep-2 and CVB4 cells.

Emodin together with an ethyl acetate subfraction F3 from P. cuspidatum were also indicated to slow down the Epstein–Barr virus (EBV) lytic cycle in a dose-dependent manner at a half maximal effective concentration of 5.94 μg/mL and 4.83 μg/mL, respectively.

A 2013 in vitro study showed that Japanese knotweed can inhibit Aspergillus fumigatus, a mold that can cause allergic reactions and respiratory illness, as well as Staphylococcus aureus, a bacterium that under the right conditions can cause an antibiotic-resistant infection.

Traditional uses have prompted recent studies aimed at delineating the effects of P. cuspidatum extracts on the viability and virulence factors of Streptococcus mutans and Streptococcus sobrinus in planktonic cultures and growing on hydroxyapatite discs.

Evidence strength: In vitro and limited in vivo only. No clinical trials in humans evaluating knotweed as an antimicrobial treatment have been identified in the peer-reviewed literature. All antimicrobial claims are based on laboratory and animal evidence.

5.6 Respiratory Tract Infections

A systematic review was carried out to evaluate the available randomized controlled trials (RCTs) of Japanese knotweed as a single herb, or as a component of a complex herbal formula for respiratory tract infections. These compounds have been identified as responsible for some of the key medicinal actions including antiviral and anti-inflammatory activities. Eight of the included RCTs used Japanese knotweed as part of a herbal formula in which a total of 1,123 subjects were enrolled. The complexity of multi-herb formulas used in these RCTs makes it impossible to isolate the specific contribution of knotweed from other co-administered herbs.

Evidence strength: Weak. Available RCT evidence uses knotweed predominantly as part of multi-herb formulations, making it impossible to isolate its independent contribution. More rigorous single-herb human trials are needed.

5.7 Hepatoprotective and Liver Effects

Emerging evidence indicates that emodin possesses a wide spectrum of pharmacological properties, including anticancer, hepatoprotective, anti-inflammatory, antioxidant, and antimicrobial activities. The hepatoprotective effects of both resveratrol and emodin have been documented in animal models, with mechanisms including reduction of oxidative stress and modulation of hepatic enzyme activity. Human-specific clinical data on knotweed for liver disease is, however, limited.

Evidence strength: Predominantly animal/in vitro. The evidence for hepatoprotection derives mainly from rodent studies and cell culture models. No high-quality RCTs in humans specifically evaluating knotweed extract for liver disease have been identified.

5.8 Anticancer Properties

Crude extract of P. cuspidatum (25, 50, 100, 200, 400 μg/mL) could inhibit the activity of human breast cancer cells and ovarian cancer cells, as well as promote cancer cell apoptosis in a dose- and time-dependent manner, with IC50 values of 31.18 ± 1.95 μg/mL and 28.12 ± 1.07 μg/mL, respectively.

To the best of available knowledge, no data regarding the potential anticancer activity of knotweed extracts in humans has been published as of recent reviews. All anticancer data come from in vitro cell culture or animal model experiments.

Evidence strength: Preclinical only. Laboratory studies are intriguing but no human clinical evidence exists for knotweed or its isolated constituents as cancer treatments. These findings should not be interpreted as clinical efficacy.

6. Body Systems and Health Areas Associated with Knotweed

• Cardiovascular system: Studies suggest Japanese knotweed extracts may help reduce inflammation, lower blood pressure, improve lipid profiles, and demonstrate antioxidant effects that protect cardiovascular tissues.
• Central nervous system: Preliminary research indicates potential neuroprotective effects, possibly due to resveratrol's ability to cross the blood-brain barrier.
• Immune system: Research has found that Japanese knotweed extract stimulated immune cells and enhanced immune functions like phagocytosis, a cellular process that can help destroy harmful microbes.
• Hepatic (liver) system: Hu Zhang is frequently used as a hepatoprotective and cholagogic drug in TCM.
• Metabolic system: Metabolic effects have generated research interest, with laboratory studies suggesting resveratrol may influence insulin sensitivity and glucose metabolism, primarily through cellular mechanisms including sirtuin activation.
• Musculoskeletal and inflammatory system: An animal study examining analgesic and anti-inflammatory effects of Japanese knotweed for arthritis treatment revealed that within three days of treatment, joint swelling was significantly reduced, in addition to decreased inflammatory markers CRP and rheumatoid factor (RF).
• Oral health: The root of P. cuspidatum has been used in Korea to maintain oral hygiene and to control oral diseases, particularly biofilm-related diseases.
• Skin: Further studies have demonstrated mechanisms by which Japanese knotweed may be applied for skin inflammations, burns, and scalds.

7. Dosage Forms and Dosages Reported in Studies

Clinical evidence on which to base dosing guidelines is limited. One clinical study used an oral extract of P. cuspidatum 200 mg containing resveratrol 40 mg over 6 weeks for anti-inflammatory effect.

Clinical trial dosages provide the best guidance: knotweed-specific trials used 200 mg knotweed extract containing 40 mg trans-resveratrol, taken daily for 6 weeks. Meta-analysis data suggests doses of 300 mg/day or higher of resveratrol for cardiovascular effects. General resveratrol trials have used dosages ranging from 20 mg to 2,000 mg/day, though higher doses carry increased side effect risk.

In a clinical trial with healthy volunteers, 500 mg/day resveratrol for 10 days significantly decreased the metabolite-to-parent ratio of carbamazepine and increased the AUC of carbamazepine by 1.5-fold, indicating inhibition of CYP3A4.

In a human pharmacokinetic study, a dose of 1 g daily resveratrol for 4 weeks was shown to inhibit CYP2C9 by 2.71-fold using losartan as a probe drug.

In available research, most studies utilize extracts standardized to contain 50–200 mg of resveratrol per day. Standardization is critical as the active compound content can vary significantly based on plant part used, harvest time, growing conditions, and extraction methods.

8. Safety Considerations and Drug Interactions

8.1 General Safety Profile

Huzhang (Japanese Knotweed) has been used in traditional Chinese medicine as well as in Japan and Korea for many years. Although used for various applications, few clinical studies validate claims, and guidance regarding dosing or safety is limited. Knotweed also contains emodin, which adds potential gastrointestinal side effects. Mild to moderate digestive discomfort is the most commonly reported side effect.

8.2 Emodin-Specific Toxicity

Emodin could lead to hepatotoxicity, kidney toxicity, and reproductive toxicity, particularly in high doses and with long-term use. Pharmacokinetic studies have demonstrated that emodin has poor oral bioavailability in rats because of its extensive glucuronidation.

Emodin, a bioactive compound abundant in Chinese medicinal herbs, possesses broad therapeutic potential but raises safety concerns due to conflicting reports of hepatotoxicity. Emodin (25–100 μM) elicited dose-dependent cytotoxicity in HepG2 cells, with the cytochrome P450 (CYP) enzymes CYP1A2 and CYP3A4 identified as the primary enzymes metabolizing emodin into hydroxylated products.

Toxic effects of emodin, such as nephrotoxicity, hepatotoxicity, genotoxicity, and reproductive toxicity, have been reported in cell and animal studies. The dose dependency of these effects is an important consideration; the toxicological risk at doses present in typical commercial supplements has not been fully characterized in human clinical studies.

8.3 Drug Interactions: Cytochrome P450 System

Resveratrol can inhibit certain CYP450 enzymes (e.g., CYP3A4, CYP1A2, and CYP2C9), altering the speed at which the body processes other medications. This change in metabolic rate usually increases the drug concentration in the bloodstream.

In a clinical trial with healthy volunteers, 500 mg/day resveratrol for 10 days significantly decreased the metabolite-to-parent ratio of carbamazepine (an anticonvulsant) and increased the AUC of carbamazepine by 1.5-fold, indicating inhibition of CYP3A4. This represents a clinically documented herb-drug interaction specific to resveratrol, the primary active constituent from knotweed.

Given the role that CYP2C9 plays in the metabolism of drugs with narrow therapeutic indices, even minor interactions could potentially impact the efficacy of these drugs. Drugs metabolized by CYP2C9 include the anticoagulant (S)-warfarin and various non-steroidal anti-inflammatory drugs.

8.4 Interaction with Anticoagulants

In rats orally given warfarin (0.2 mg/kg) without and with resveratrol (100 mg/kg) in a parallel design, resveratrol significantly increased the AUC of S-warfarin and the international normalized ratio. Mechanism studies showed that both resveratrol and its serum metabolites inhibited BCRP-mediated efflux of R- and S-warfarin. Resveratrol's serum metabolites activated CYP1A2/3A4 but inhibited CYP2C9. The co-intake of resveratrol increased the systemic exposure of warfarin and enhanced the anticoagulation effect mainly via inhibitions on BCRP and CYP2C9.

Theoretical bleeding risk exists when combining resveratrol with anticoagulants (warfarin, DOACs) or antiplatelet drugs (clopidogrel, aspirin). Resveratrol's mild antiplatelet properties present a concern when combined with medications prescribed to manage or prevent blood clots. The combined action of the supplement and the drug creates an additive or synergistic effect, leading to a high risk of bleeding.

8.5 Reproductive and Hormonal Considerations

Emodin could lead to reproductive toxicity, particularly in high doses and with long-term use. Resveratrol has also been studied for potential estrogenic activity. The clinical significance of these effects at supplemental doses in humans has not been definitively established.

8.6 Regulatory Status

The rhizome and root (Polygoni cuspidati rhizoma et radix) was included in the European Pharmacopoeia in 2017 among herbal drugs. P. cuspidatum extracts, particularly for resveratrol, are widely used in dietary supplements, but they lack formal GRAS (Generally Recognized as Safe) status from the US FDA. In the UK, trans-resveratrol is authorized as a novel food with a maximum daily intake of 150 mg for adults; it is regulated as a food supplement, not a medicine.

9. Overall Evidence Assessment

The strongest evidence still comes from laboratory studies, animal models, and traditional use rather than large modern clinical trials of the herb by itself. Japanese knotweed is a serious medicinal plant with real bioactive compounds, but it is best approached as a targeted herb with a specific profile.

Laboratory studies suggest potential cardiovascular, metabolic, and anti-inflammatory effects, but large-scale clinical trials demonstrating definitive benefits remain limited. Despite promising results, most studies are preclinical or small-scale human trials. Larger, long-term clinical trials are still needed to fully confirm efficacy and establish definitive therapeutic guidelines for specific diseases.

Further clinical research in human subjects would offer a more effective insight and allow for a more rigorous understanding of the therapeutic potential of Japanese knotweed for the medicinal actions studied to date.

References

• Peng W, et al. "A Review of the Pharmacological Effects of the Dried Root of Polygonum cuspidatum (Hu Zhang) and Its Constituents." Evidence-Based Complementary and Alternative Medicine, 2013. PMC3806114
• Cucu AA, et al. "New Approaches on Japanese Knotweed (Fallopia japonica) Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions." Plants (Basel), 2021. PMC8705504
• Advances for pharmacological activities of Polygonum cuspidatum – A review. Taylor & Francis / PMC, 2023. PMC9833411
• Dong X, et al. "Emodin: A Review of its Pharmacology, Toxicity and Pharmacokinetics." Phytotherapy Research, 2020. PMC7168079
• Chow HH, et al. "Effects of resveratrol on drug- and carcinogen-metabolizing enzymes, implications for cancer prevention." Cancer Prevention Research, 2017. PMC5461649
• Resveratrol stereoselectively affected (±)warfarin pharmacokinetics and enhanced the anticoagulation effect. Scientific Reports, 2020. PMC7522226
• Trans-Resveratrol Enhances the Anticoagulant Activity of Warfarin in a Mouse Model. PMC5090816
• Evidence of Clinical Efficacy and Pharmacological Mechanisms of Resveratrol in the Treatment of Alzheimer's Disease. PMC10825797
• Neuroprotective Mechanisms of Resveratrol in Alzheimer's Disease: Role of SIRT1. PMC6232815
• Unraveling the therapeutic efficacy of resveratrol in Alzheimer's disease: an umbrella review of systematic evidence. PMC10953289
• Smoliga JM, et al. "Resveratrol and Clinical Trials: The Crossroad from In Vitro Studies to Human Evidence." Carbon, 2013. PMC3782695
• Resveratrol and Neuroprotection: Impact and Its Therapeutic Potential in Alzheimer's Disease. PMC7804889
• In Vitro Comparison of the Bioactivities of Japanese and Bohemian Knotweed Ethanol Extracts. PMC7278624
• Effect of clone selection, nitrogen supply, leaf damage and mycorrhizal fungi on stilbene and emodin production in knotweed. PMC3123627
• ScienceDirect – Polygonum cuspidatum Overview (Pharmacology and Pharmaceutical Science)
• Drugs.com Natural Product Monograph: Japanese Knotweed (Polygonum cuspidatum). Medically reviewed, last updated July 2025.
• Fallopia japonica: Bioactive Secondary Metabolites and Molecular Mode of Anticancer. OMICS International.
• Japanese Knotweed (Reynoutria japonica): Uses, Safety, Benefits. Herbal Reality, 2026.
• Advances for pharmacological activities of Polygonum cuspidatum – A review. PubMed 36620922
• Cytochrome P450-mediated detoxification and NF-κB/NLRP3 pathway-driven hepatotoxicity of emodin. PubMed 41579920
• Chen H, et al. "Quality Assessment of Japanese Knotweed (Fallopia japonica) Grown on Prince Edward Island as a Source of Resveratrol." Journal of Agricultural and Food Chemistry, 2013.
• Klemow KM. "Medical attributes of Polygonum cuspidatum – Japanese knotweed." Wilkes University.