Home Ingredients Knotgrass (Polygonum aviculare)

Knotgrass (Polygonum aviculare)

Polygonum aviculare
Evidence Level
Preliminary
4 Clinical Trials
5 Documented Benefits
1/5 Evidence Score

Knotgrass (Polygonum aviculare) is a low, sprawling weed of fields and roadsides in the buckwheat family whose dried flowering aerial parts are brewed as a tea; in Chinese tradition it is called Bian Xu. The herb contains flavonoids, mainly flavonol glucuronides and quercetin and kaempferol derivatives such as avicularin, plus tannins (about 3.5 to 4% in reference texts) and phenolic acids. The European Medicines Agency lists it as a traditional herbal medicine taken as a tea for relief of common cold symptoms and to increase urine flow in minor urinary complaints, based on long-standing use rather than clinical trials. No controlled trial of knotgrass taken by mouth was found. The only human study tested a mouth rinse that was not swallowed; the rest of the research is lab and animal work. It is not recommended for children under 12 or during pregnancy or breastfeeding.

Studied Dose No human dose of knotgrass taken by mouth has been tested in a controlled trial. EU traditional tea: 1.5 to 2 g of herb in 150 mL boiling water 3 to 4 times daily (4.5 to 8 g/day) for colds, or 3 g as a decoction twice daily (6 g/day) for urine flow.
Active Compound Flavonoids (at least 0.30% as hyperoside in the European Pharmacopoeia herb; 0.70 to 2.20% in commercial and wild samples), mainly flavonol glucuronides and quercetin and kaempferol glycosides such as avicularin and juglanin, plus tannins (3.5 to 4% in reference texts) and phenolic acids such as caffeic and chlorogenic acid.

Benefits

Traditional European tea for seasonal throat and airway comfort

The European Medicines Agency's herbal committee accepts knotgrass tea as a traditional herbal medicine for relief of common cold symptoms in adolescents and adults, for up to 1 week. This rests only on long-standing use: the committee found no clinical data for this use, so it did not accept well-established use.

Supported by Trial 2, Trial 3

Traditional tea use to increase urine flow and flush the urinary tract

The same EU monograph accepts a knotgrass decoction to increase the amount of urine and flush the urinary tract alongside minor urinary complaints, with enough fluid intake, for up to 2 weeks. It is based on long-standing use, not on trials; no study measuring urine output in people taking knotgrass was found.

Supported by Trial 1, Trial 2

Calcium oxalate crystal deposits in rat kidneys (animal study)

In rats given ethylene glycol and ammonium chloride to induce kidney crystals, a water extract of knotgrass given by mouth tube at 100 or 400 mg/kg for 28 days reduced calcium oxalate crystal counts and tissue changes, whether started at the beginning or halfway through. This is an animal model, not a result in people.

Supported by Trial 1

Body fat and blood fats in mice on a high-fat diet (animal study)

Mice fed a high-fat diet with a knotgrass ethanol extract (400 mg/kg a day for 6.5 weeks) gained less weight and fat tissue and had lower blood triglycerides and leptin than untreated obese mice, and the extract reduced fat build-up in cultured fat cells. No human weight or blood-fat study exists.

Supported by Trial 2

Immune-cell and inflammation signals in lab tests

Flavonol glucuronides isolated from knotgrass reduced reactive oxygen species and elastase release from human neutrophils in test tubes at 0.5 to 10 micromolar, and a water extract inhibited prostaglandin production and platelet activating factor induced exocytosis in test-tube assays. These are lab findings only.

Supported by Trial 3

Mechanism of action

1

Flavonoid and tannin content

Knotgrass herb is standardized on flavonoids, and lab analyses show flavonol glucuronides of quercetin, kaempferol, myricetin and isorhamnetin dominate, with total flavonoids of 0.70 to 2.20% in commercial and wild samples. Reference texts give 3.5 to 4% tannins. European regulators identified no constituent with known therapeutic activity.

2

Antioxidant and anti-inflammatory activity in the lab

An ethanol extract scavenged free radicals and superoxide and protected DNA from hydroxyl radical damage in test-tube assays, and isolated flavonol glucuronides lowered oxidant and elastase release from human neutrophils. Whether these effects occur after drinking the tea is unknown.

3

Airway muscle relaxation through calcium channels in lab tissue

In mouse and human airway smooth muscle tested in the lab, an ethyl acetate fraction of knotgrass and its flavonoid quercetin reduced contraction by blocking several calcium-permeable channels (L-type calcium, TRPC3 and STIM/Orai). This is tissue work, not a breathing study in people.

Clinical trials

1
Knotgrass Water Extract and Kidney Crystals in Rats: Animal Study
PubMed

Randomized animal study of an aqueous knotgrass extract given by gavage at 100 or 400 mg/kg for 28 days, as prevention (from day 1) or treatment (from day 14), in rats given ethylene glycol and ammonium chloride in drinking water. (Saremi et al. 2018, Urol J)

64 male Wistar rats in 8 groups of 8; no people.

Compared with untreated crystal-induced rats, calcium oxalate crystal counts and tubulointerstitial changes were lower in the prevention groups (P < .001) and the treatment groups (P < .05). Healthy rats given the extract alone did not show the crystal increase seen in untreated crystal-induced rats. Rat models of induced crystals do not show what knotgrass tea does in people.

2
Knotgrass Ethanol Extract in High-Fat-Diet Mice: Animal and Cell Study
PubMed

Animal and cell study by the Korea Institute of Oriental Medicine; mice fed a high-fat diet with or without a knotgrass ethanol extract at 400 mg/kg a day for 6.5 weeks, plus 3T3-L1 fat cell experiments. (Sung et al. 2013, Evid Based Complement Alternat Med)

Mice with diet-induced obesity and cultured mouse fat cells; no people.

The extract reduced body weight gain, fat tissue weight, fat cell size, and serum triglycerides, leptin and malondialdehyde versus untreated obese mice, and lowered expression of fat-making genes. In cells it blocked fat cell maturation and fat build-up in a dose-dependent way. No human study has tested these effects.

3
Knotgrass Flavonol Glucuronides on Human Neutrophils: Lab Study
PubMed

Isolation of 11 flavonol glucuronides from European Pharmacopoeia knotgrass herb and testing on human neutrophils in vitro. (Granica et al. 2013, Fitoterapia)

Neutrophils isolated from human blood, tested in test tubes; no one took knotgrass.

All 11 compounds, at 0.5 to 10 micromolar, significantly inhibited reactive oxygen species production and elastase release, and the authors proposed them as contributors to the herb's anti-inflammatory activity. Eight had not been reported in Polygonum species before. Whether these concentrations are reached in people drinking the tea was not tested.

4
Knotgrass Extract and Quercetin on Airway Smooth Muscle: Lab Tissue Study
PubMed

Lab study screening herbs for effects on precontracted mouse and human airway smooth muscle, with channel current recordings. (Luo et al. 2018, Sci Rep)

Isolated mouse and human airway smooth muscle tissue and cells; no one took knotgrass by mouth.

An ethyl acetate fraction of knotgrass inhibited precontraction of airway smooth muscle and blocked L-type calcium, TRPC3 and STIM/Orai channel currents; quercetin, present in the extract, did the same. The authors suggested knotgrass as a source for new bronchodilator drugs, but no breathing study in people was done.

Side effects and drug interactions

Common Potential side effects

The EU herbal monograph lists no known undesirable effects, and its assessment found no reported adverse events; however, conventional clinical safety data for knotgrass taken by mouth are absent.
Not recommended for children under 12, or during pregnancy or breastfeeding, because safety has not been established. No fertility data are available.
Tests for genotoxicity, cancer risk and reproductive toxicity have not been done; for that reason the EU did not add knotgrass to its list of herbal substances.
Do not use if allergic to knotgrass. When used to increase urine flow, drink enough fluid, and avoid it if a doctor has advised reduced fluid intake, for example in severe heart disease.
See a doctor if fever, painful urination, cramping or blood in the urine appear, if urinary complaints last more than 2 weeks, or if cold symptoms worsen or last more than 1 week.

Important Drug interactions

None are reported in the EU herbal monograph, and no interaction studies have been done.
Diuretic medicines or a prescribed fluid limit: knotgrass is used traditionally to increase urine flow, so ask a clinician before combining them, even though no interaction cases are known.

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Frequently asked questions about Knotgrass (Polygonum aviculare)

Does drinking knotgrass tea help the gums?

That has not been tested. The only gum study used a knotgrass extract as a mouth rinse for 2 weeks, without a control group, and found a small drop in gum inflammation scores alongside more plaque. European assessors judged it weak and did not accept a gum use. Because the rinse was not swallowed, it says nothing about knotgrass taken by mouth as a supplement.

Is knotgrass the same as Japanese knotweed or He Shou Wu?

No. They are different plants in the same broad Polygonum group. Japanese knotweed (Polygonum cuspidatum) and He Shou Wu (Polygonum multiflorum) have their own chemistry and research. The European constituent list for knotgrass names flavonoids, tannins and phenolic acids, not stilbenes such as resveratrol, so check the Latin name on the label.

How does knotgrass compare with agrimony and tormentil?

All three are traditional European tannin-containing teas with EU traditional-use monographs. Knotgrass is in the buckwheat family and is standardized on flavonoids, with about 3.5 to 4% tannins in reference texts, while tormentil rhizome must contain at least 7% tannins. Agrimony and tormentil each have one placebo-controlled oral trial; knotgrass has none.

Why should fluid intake go up when knotgrass is used for the urinary tract?

The traditional aim is to flush the urinary tract by increasing urine, and the EU monograph says adequate fluid intake is required for that. For the same reason it should not be used where a doctor has advised drinking less, for example in severe heart disease. Fever, painful urination, cramping or blood in the urine need medical attention.

What is Knotgrass?

Knotgrass (Polygonum aviculare) is a low, sprawling weed of fields and roadsides in the buckwheat family whose dried flowering aerial parts are brewed as a tea; in Chinese tradition it is called Bian Xu.

What is Knotgrass used for?

NutraSmarts does not list Knotgrass under a health category. What the research covers: The European Medicines Agency's herbal committee accepts knotgrass tea as a traditional herbal medicine for relief of common cold symptoms in adolescents and adults, for up to 1 week.

What is the recommended dosage of Knotgrass?

No human dose of knotgrass taken by mouth has been tested in a controlled trial. EU traditional tea: 1.5 to 2 g of herb in 150 mL boiling water 3 to 4 times daily (4.5 to 8 g/day) for colds, or 3 g as a decoction twice daily (6 g/day) for urine flow. Always follow the product label and check with a healthcare provider for personal advice.

Is Knotgrass safe, and does it have side effects?

Side effects and cautions reported for Knotgrass include: The EU herbal monograph lists no known undesirable effects, and its assessment found no reported adverse events; however, conventional clinical safety data for knotgrass taken by mouth are absent. It may also interact with some medications. Knotgrass is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Knotgrass interact with any medications?

Possible interactions include: None are reported in the EU herbal monograph, and no interaction studies have been done. Diuretic medicines or a prescribed fluid limit: knotgrass is used traditionally to increase urine flow, so ask a clinician before combining them, even though no interaction cases are known. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Knotgrass?

NutraSmarts rates the evidence for Knotgrass as Preliminary (1 out of 5). It is backed by 4 study summaries and 12 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(12 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). European Union herbal monograph on Polygonum aviculare L., herba. Final. EMA/HMPC/143658/2015. European Medicines Agency. 2016;Adopted by HMPC 4 February 2016; dated 5 April 2016 (not PubMed-indexed)..SourceUsed to support: Not PubMed-indexed. Traditional-use monograph based exclusively on long-standing use, with two oral indications: a herbal tea for relief of common cold symptoms (1.5 to 2 g in 150 mL, 3 to 4 times daily, 4.5 to 8 g/day; see a doctor if symptoms last over 1 week) and a decoction to increase urine and flush the urinary tract in minor urinary complaints (3 g in 200 mL twice daily, 6 g/day, with adequate fluid; see a doctor if symptoms last over 2 weeks). Not recommended under 12 or in pregnancy and lactation; contraindicated in hypersensitivity and, for the urinary use, where reduced fluid intake is advised; no interactions reported; no known undesirable effects; genotoxicity, carcinogenicity and reproductive toxicity tests not performed.
  2. European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Assessment report on Polygonum aviculare L., herba. Final. EMA/HMPC/143659/2015. European Medicines Agency. 2016;Dated 5 April 2016 (not PubMed-indexed)..SourceUsed to support: Not PubMed-indexed. Reports no clinical data for the monograph indications, so well-established use is not accepted; the only clinical study found was a mouth-rinse gingivitis study judged methodologically weak, and a gingivitis indication was not supported. Lists constituents as flavonoids (0.1 to 1%), tannins (3.5 to 4%) and phenolic acids, notes the Ph. Eur. minimum of 0.30% flavonoids as hyperoside, records the Chinese name Bian Xu, finds no reported adverse events, notes no genotoxicity data (so no EU list entry), and identifies no constituent with known therapeutic activity.
  3. González Begné M, Yslas N, Reyes E, Quiroz V, Santana J, Jimenez G. Clinical effect of a Mexican sanguinaria extract (Polygonum aviculare L.) on gingivitis. J Ethnopharmacol. 2001;74(1):45-51. doi: 10.1016/s0378-8741(00)00338-x.PubMedUsed to support: A topical study (mouth rinse, not swallowed), cited only to show that the one human study of knotgrass did not involve oral use. Single-group study without a control group in 60 male dentistry students aged 18 to 25: a knotgrass extract rinse (1 mg/ml) twice daily for 2 weeks with no tooth-brushing lowered the gingivitis index slightly (1.056 to 1.011) while dental plaque rose (91.38 to 98.69).
  4. Granica S. Quantitative and qualitative investigations of pharmacopoeial plant material polygoni avicularis herba by UHPLC-CAD and UHPLC-ESI-MS methods. Phytochem Anal. 2015;26(5):374-82. doi: 10.1002/pca.2572.PubMedUsed to support: Analysis of nine commercial and wild samples of knotgrass herb: 25 major constituents detected, flavonol glucuronides were the major compounds in all samples, and total flavonoid content ranged from 0.70 to 2.20%. The author suggests the pharmacopoeial standardization approach should be revised.
  5. Granica S, Piwowarski JP, Popławska M, Jakubowska M, Borzym J, Kiss AK. Novel insight into qualitative standardization of Polygoni avicularis herba (Ph. Eur.). J Pharm Biomed Anal. 2013;72:216-22. doi: 10.1016/j.jpba.2012.08.027.PubMedUsed to support: Chemical analysis: flavonoids are the main active constituents on which knotgrass herb is standardized, and myricetin, kaempferol, isorhamnetin and kaempferide glucuronides, not previously reported in the herb, were among the dominant compounds.
  6. Granica S, Czerwińska ME, Żyżyńska-Granica B, Kiss AK. Antioxidant and anti-inflammatory flavonol glucuronides from Polygonum aviculare L. Fitoterapia. 2013;91:180-188. doi: 10.1016/j.fitote.2013.08.026.PubMedUsed to support: Lab study: 11 flavonol glucuronides were isolated from knotgrass herb (8 new to Polygonum species), and all of them at 0.5 to 10 micromolar significantly inhibited reactive oxygen species production and elastase release by human neutrophils in vitro. No human intake tested.
  7. Tunón H, Olavsdotter C, Bohlin L. Evaluation of anti-inflammatory activity of some Swedish medicinal plants. Inhibition of prostaglandin biosynthesis and PAF-induced exocytosis. J Ethnopharmacol. 1995;48(2):61-76. doi: 10.1016/0378-8741(95)01285-l.PubMedUsed to support: In vitro screen of 59 water extracts from 52 plants used in Swedish traditional medicine: the Polygonum aviculare extract was active in both the prostaglandin biosynthesis and the PAF-induced exocytosis assays. No human data.
  8. Hsu CY. Antioxidant activity of extract from Polygonum aviculare L. Biol Res. 2006;39(2):281-8. doi: 10.4067/s0716-97602006000200010.PubMedUsed to support: Test-tube study: a lyophilized ethanol extract of knotgrass scavenged free radicals (IC50 50 micrograms/ml) and superoxide (IC50 0.8 micrograms/ml), inhibited lipid peroxidation (IC50 15 micrograms/ml) and protected DNA from hydroxyl radical strand breaks. No human data.
  9. Saremi J, Kargar Jahromi H, Pourahmadi M. Effect of Polygonum Aviculare L. on Nephrolithiasis Induced by Ethylene Glycol and Ammonium Chloride in Rats. Urol J. 2018;15(3):79-82. doi: 10.22037/uj.v0i0.3815.PubMedUsed to support: Rat study: in 64 male Wistar rats, an aqueous knotgrass extract (100 or 400 mg/kg by gavage) reduced calcium oxalate crystal counts and tubulointerstitial changes from ethylene glycol and ammonium chloride, both as prevention (P < .001) and as treatment from day 14 (P < .05). Animal evidence only.
  10. Sung YY, Yoon T, Yang WK, Kim SJ, Kim DS, Kim HK. The Antiobesity Effect of Polygonum aviculare L. Ethanol Extract in High-Fat Diet-Induced Obese Mice. Evid Based Complement Alternat Med. 2013;2013:626397. doi: 10.1155/2013/626397.PubMedUsed to support: Mouse and cell study: a knotgrass ethanol extract (400 mg/kg/day for 6.5 weeks) lowered body weight gain, fat tissue, fat cell size and serum triglycerides, leptin and malondialdehyde in high-fat-diet mice, and inhibited fat cell differentiation in 3T3-L1 cells. Animal and cell evidence only.
  11. Luo X, Xue L, Xu H, Zhao QY, Wang Q, She YS, Zang DA, Shen J, Peng YB, Zhao P, Yu MF, Chen W, Ma LQ, Chen S, Chen S, Fu X, Hu S, Nie X, Shen C, Zou C, Qin G, Dai J, Ji G, Su Y, Hu S, Chen J, Liu QH. Polygonum aviculare L. extract and quercetin attenuate contraction in airway smooth muscle. Sci Rep. 2018;8(1):3114. doi: 10.1038/s41598-018-20409-x.PubMedUsed to support: Lab tissue study: an ethyl acetate fraction of knotgrass and quercetin inhibited precontraction of mouse and human airway smooth muscle by blocking L-type calcium, TRPC3 and STIM/Orai channels. No oral or human intake data.
  12. Idoudi S, Tourrette A, Bouajila J, Romdhane M, Elfalleh W. The genus Polygonum: An updated comprehensive review of its ethnomedicinal, phytochemical, pharmacological activities, toxicology, and phytopharmaceutical formulation. Heliyon. 2024;10(8):e28947. doi: 10.1016/j.heliyon.2024.e28947.PubMedUsed to support: Review of the Polygonum genus: covers several species used in traditional medicine, including P. aviculare, P. cuspidatum, P. multiflorum, P. minus and P. hydropiper, which differ in chemistry; across the genus it lists phenolic acids, flavonoids, tannins and stilbenes such as polydatin and resveratrol, with activities shown mainly in lab and animal studies.