japanese armor weed extract

Japanese Knotweed

Scientific Name(s): Polygonum cuspidatum Siebold & Zucc.
Common Name(s): Fleeceflower, Huzhang, Japanese bamboo, Japanese knotweed, Mexican bamboo

Medically reviewed by Last updated on Dec 25, 2019.

Clinical Overview

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.

For information specific to the activity of resveratrol, see Resveratrol.


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.



Do not use. Avoid use during lactation because information is lacking.


None well documented.

Adverse Reactions

Clinical evidence is limited.


Information is limited.

Scientific Family

  • Polygonaceae (Buckwheat)


P. cuspidatum is a perennial plant growing to approximately 2 m tall. It has mucous hollow stems with reddish purple spots and ovate/elliptical deciduous leaves (5 to 12 cm by 4 to 9 cm). The male and female flowers occur on separate plants, and the fruits are black/brown, shiny, and ovoid. The plant is native to eastern Asia, including Japan, China, and Korea. It is cultivated in those countries and in the US, and is propagated by seeds or the root. Synonyms include Pleuropterus cuspidatus (Siebold & Zucc.) Moldenke, Fallopia japonica (Houtt.) Ronse Decr., Pleuropterus zuccarinii (Small) Small, Polygonum cuspidatum Siebold & Zucc. var. compactum (Hook. f.) L.H. Bailey, and Reynoutria japonica Houtt.

Because of the plant’s spreading rhizomes, P. cuspidatum is grown commercially as a major source for resveratrol production (see Resveratrol monograph), while also being considered a noxious, invasive class B or C weed in certain US states.Chen 2013, Peng 2013, USDA 2013


At least 100 prescriptions using the root exist in the Pharmacopoeia of the People’s Republic of China to treat bronchitis and cough, gonorrhea, inflammation, infection, jaundice, hyperlipidemia and hypertension, menopausal symptoms and amenorrhea, and skin burns. The root is used extensively in traditional medicine in China, Japan, and Korea, and the young plant parts are eaten as a vegetable. P. cuspidatum is a primary source of resveratrol, which is widely available in the United States as a botanical dietary supplement.Hao 2012, Li 2013, Peng 2013


Volatile essential oils are described for the leaves, but the roots are the main plant part used traditionally. Major constituent chemicals include quinines (eg, anthraquinone, naphthoquinone, phylloquinone) and emodin-type anthroquinones, stilbenes (eg, resveratrol, piceatannol polydatin), flavonoids (eg, quercetin, catechin, rutin), coumarins, lignans, and other compounds.Chen 2012, Du 2013, Hao 2012, Kirino 2012, Li 2013, Peng 2013, Piotrowska 2012, Shen 2011, Zhang 2012

Emodin and phsycion demonstrate anti-inflammatory effects.Shen 2011 The stilbene content, including resveratrol, resveratroloside, polydatin, and piceatannol, are responsible for observed antioxidant activity.Kirino 2012, Piotrowska 2012

Methods of identification have been published, including high-performance liquid chromatography and thin-layer chromatography, which are based on the content of emodin and polydatin (minimum concentrations of 0.6% and 0.15%, respectively, per the Chinese pharmacopoeia). Chemical composition varies seasonally and with harvest time.Babu 2005, Chen 2013, Hao 2012, Peng 2013

Uses and Pharmacology

Research reveals no clinical data regarding the use of Japanese knotweed for antioxidant effect.

Anti-inflammatory effects

Animal data

Reductions in inflammation and improvements in wound-healing rates were demonstrated with topical application of P. cuspidatum extract in studies in mice.Bralley 2008, Peng 2013, Wu 2012 With oral extract reductions in tumor necrosis factor alpha (TNF-alpha), interleukin (IL-6) and C-reactive protein were found in animals with experimentally induced arthritis.Han 2012 An analgesic effect was also demonstrated in rodents.Han 2012

Clinical data

Limited clinical studies have been conducted. A study among healthy volunteers found a decreased expression of modulators of inflammation in mononuclear cells following 6 weeks of P. cuspidatum extract daily containing resveratrol 40 mg.Ghanim 2010 A small study (N = 20) found decreased plasma TNF-alpha and IL-6 versus placebo.Zahedi 2013

Antimicrobial activity

Animal data

In vitro studies have shown broad antibacterial and antifungal activity of P. cuspidatum extracts.Peng 2013, Piotrowska 2012, Song 2006 Activity against Streptococcus mutans has been investigated in oral health.Ban 2010, Pandit 2012 An ethanol extract showed inhibitory activity against HIV-1 in vitro.Lin 2010, Peng 2013

Clinical data

There are no clinical data regarding the use of P. cuspidatum as an antimicrobial agent.

Antioxidant effects

Animal data

Studies in rats and mice have shown antioxidant properties of P. cuspidatum that are generally attributed to the chemical constituents of resveratrol, polydatin, piceatannol, and anthraquinones and stilbenes.Kim 2010, Peng 2013, Piotrowska 2012, Zhang 2012 Carbon tetrachloride–induced liver injury and induced acute cerebral ischemia were reduced by oral extracts of P. cuspidatum.Kim 2010, Zhang 2012 In models of vascular dementia and Parkinson disease in rats, P. cuspidatum extract and polydatin administered orally resulted in improved cognitive and behavioral measures and increased antioxidant capacity in the relevant tissues.Li 2012, Wang 2011

Clinical data

There are no clinical data regarding the use of P. cuspidatum for antioxidant effect.


Animal data

In vitro studies using oral, lung, and prostate cancer cells, and in hepatocarcinoma, glioma, and leukemia have been conducted. Ethanol, methanol and aqueous P. cuspidatum extracts show pro-apoptotic activity and inhibition of angiogenesis, as well as direct cytotoxicity.Hu 2012, Jeong 2010, Lin 2010, Shin 2011 Mice with Ehrlich carcinoma had an increased lifespan when given P. cuspidatum extract.Peng 2013

Clinical data

Research reveals no clinical data for the use of P. cuspidatum regarding cancer.


Animal data

Studies conducted in the 1980s and 1990s in rodent models of hyperlipidemia showed decreased total cholesterol, as well as decreased triglycerides and low-density lipoprotein.Peng 2013 Oral polydatin from P. cuspidatum showed similar results in rabbits and hamsters.Du 2009, Xing 2009

Clinical data

There are no clinical data regarding the use of P. cuspidatum in hyperlipidemia.


Clinical evidence on which to base dosing guidelines is lacking. One study used an oral extract of P. cuspidatum 200 mg over 6 weeks. The preparation was standardized to contain resveratrol 40 mg.Zahedi 2013

Topical application of P. cuspidatum extract has been studied in mice for anti-inflammatory effects.Bralley 2008, Wu 2012

Pregnancy / Lactation

Do not use in pregnancy. Huzhang is listed as an abortifacient in traditional Chinese medicine texts.Peng 2013

Avoid use during lactation; information regarding use during lactation is lacking.


The area under the curve of carbamazepine and its active metabolite were increased in rats fed P. cuspidatum, suggesting an increased risk of carbamazepine toxicity.Chi 2012

Adverse Reactions

Clinical evidence on which to base guidance is limited. A study conducted in basketball players over 6 weeks did not report adverse events.Zahedi 2013


Information is limited.Du 2013, Peng 2013 The oral median lethal dose (LD50) of anthraquinones in mice is approximately 9 g/kg body weight. The LD50 of emodin and polydatin is 250 and 1,000 mg/kg, respectively. Parenteral polydatin caused peritonitis in a subacute toxicity test in animals. No hemolysis, agglutination reaction, or systemic anaphylaxis/skin allergy was found in tests conducted in rabbits.Peng 2013

Index Terms

  • Fallopia japonica (Houtt.) Ronse Decr.
  • Pleuropterus cuspidatus (Siebold & Zucc.) Moldenke
  • Pleuropterus zuccarinii (Small) Small
  • Polygonum cuspidatum Siebold & Zucc. var. compactum (Hook. f.) L.H. Bailey
  • Reynoutria japonica Houtt



This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.

This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.

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Further information

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Learn about the potential benefits of Japanese Knotweed including contraindications, adverse reactions, toxicology, pharmacology and historical usage.

Do the Herbs in Natural Erection Supplements Really Make You Harder?

The companies that market so-called “natural” sexual health supplements make a lot of promises, especially when they’re pitching more frequent and harder erections. But do the herbs they put in those pills actually, y’know. work?

Last month, a group of urologists from the Wake Forest School of Medicine checked for you . They surveyed the 30 best-selling male sexual health “nutraceuticals” and combed through the published literature looking for medical research on the most frequently used ingredients.

Here’s what they learned about the science behind the 5 most frequently used herbs on the list.

Ginseng (Panax sp.)

The Plant: The name ginseng can refer to any one of the 11 species in the genus Panax. All of them are perennial shrubs with large fleshy branching roots that grow in shady forest habitats.

The Claim: If you squint and have an excellent imagination, mature ginseng roots vaguely resemble a human body. That ties into folk ideas for finding medicines–in this case, the idea that a plant that looks like a person must contain materials that help sick people. Ginseng was traditionally used as a tonic to treat erectile dysfunction and low sexual drive in men (as well as many other complaints).

The Science: Chemicals inside these plants called ginsenosides are thought to ramp up the physiological pathway that makes nitric oxide, the neurotransmitter that gets the blood flowing during penile erection. Some studies support that idea: one found that ginsenoside-rich ginseng berry extracts relaxed smooth muscle inside rabbit erectile tissue. But so far there haven’t been high-quality double-blind and randomized trials of the chemicals’ effect on humans. The jury’s still out on whether ginsenosides have any effect on people at all, or (if they do) whether they work as well as medications like Viagra.

Puncturevine (Tribulus terrestris)

The Plant: A low-growing flowering annual that’s originally from southern Europe but is now an invasive weed in parts of the United States and Australia. The plant’s common names, like puncturevine or devil’s thorns , tells you exactly why most people hate it: it drops sharp, spiny seed pods that lie in wait for unsuspecting victims to step on them. It’s also toxic to grazing livestock like sheep.

The Claim: Extracts from the plant are supposed to increase testosterone production, boosting libido. It’s also supposed to trigger more frequent erections and increase the volume of semen that’s ejaculated.

The Science: Though it would be nice to find a useful side to this otherwise noxious plant, double-blind studies found no significant changes in either serum testosterone levels or erectile function in the people who took extracts of T. terrestris.

Horny goat weed (Epimedium sp.)

The Plant: It’s true, the name’s hilarious. But as it turns out, it’s not just one plant: supplement manufacturers might put any one of 15 different species from this genus of shade-loving perennials inside that pill. That’s important to keep in mind, because the types and amounts of biologically active molecules the plant contains can differ from species to species.

The Claim: Epimedium contains small amounts of the chemical icariin, which inhibits the enzyme that breaks down the muscle-relaxing molecule that the penis uses to get erections underway. ( Biochemically, Viagra works the same way .)

The Science: Male rats with damaged penile nerves had better erectile responses after they were given large doses of purified icariin, but as of yet no one has done the experiments to see whether the compound works in humans. Still, as far as the herb goes, it doesn’t really matter: horny goat weed doesn’t contain enough icariin to get even the smallest rise out of a rat.

Fenugreek (Trigonella foenum-graecum)

The Plant: If you like Indian or Middle Eastern food, or prefer imitation maple syrup to the real stuff , you’ve probably eaten something flavored with fenugreek. It’s an annual leafy herb that looks a little like parsley but has a maple-like smell.

The Claim: Fenugreek contains diosgenin: a molecule that the body can turn into steroid sex hormones. It is supposed to improve the regulation of testosterone levels and increase libido.

The Science: There’s only been one double-blind placebo-controlled trial of the stuff: it found that men taking fenugreek extract reported that they felt more sexual arousal and experienced better orgasms. But testosterone levels in those same men didn’t change, and the study was also tiny–only 60 participants–so it’s not clear whether there’s actually a biochemical reason for the shift or whether it was all psychological. The experiment needs to be repeated with a larger group of people to find out whether those results can be reproduced.

Maca (Lepidium meyenii)

The Plant: A turniplike vegetable that’s cultivated in the Andes mountains. Its root is sometimes served roasted, but it’s typically dried and ground into a flour for fritters and pancakes. Its flavor has been described as an acquired taste.

The Claim: Traditionally, maca was supposed to enhance fertility, but after the first exports of the plant to Japan and North America in the 1990s, it gained a reputation as a male aphrodisiac.

The Science: Some studies have implied that feeding maca to domestic cattle increases sperm production, but there is very little data about any sexual effect on humans. One very small randomized double-bind trial of men with erectile dysfunction found that men taking maca extract reported a small increase in their ability to get erections. But so did the control group. As with the fenugreek study, a similar study with a larger group of people is needed to see whether any differences between the controls and the maca-eaters are real.

The Upshot?

It doesn’t look good for the herbs. So far, there’s no data from controlled human trials that support the erection-promoting claims for any 5 of the most frequently used herbs. The icariin in the horny goat weed can help get it up, but since you’re getting the herb rather than a purified molecule, the concentration probably isn’t high enough to have much of an effect. Worse, it turns out that Viagra is much better at blocking that erection-killing enzyme than icariin is.

And just because you’re using a “natural” herb doesn’t mean you won’t feel any side effects. Ginseng can cause hypoglycemia or bleeding in some people, and at high doses puncturevine can damage the kidneys. Plus, the FDA has found that a lot of supplement companies make sure their erection-enhancing products actually produce erections by tossing in some Viagra off-label . If you really need it, it’s probably better–and safer–to go see your doctor for a prescription.

Top image TKTK; Ginseng by Katharina Lohrie via Wikimedia | CC BY 3.0 ; Puncturevine by Forest & Kim Starr via Wikimedia | CC BY 3.0 ; Epimedium by Maja Dumat via Flickr | CC BY 2.0 ; Fenugreek by Thamizhpparithi Maari via Wikimedia | CC BY-SA 4.0 ; Maca powder by Maša Sinreih in Valentina Vivod via Wikimedia | CC BY-SA 3.0

The companies that market so-called “natural” sexual health supplements make a lot of promises, especially when they’re pitching more frequent and harder erections. But do the herbs they put in those pills actually, y’know… work?