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Knotweed (bian xu)

What is knotweed? What is it used for?

Knotweed is a member of the polygonum family, similar to fo ti. It is known by several names, including bird's tongue, cow grass and pigweed.

Knotweed contains a variety of compounds and active ingredients, including quercetin, salicylic acid (which is also found in aspirin) and lysine, and an assortment of sugars. The herb is gathered during its flowering season and dried before being used.

In traditional Chinese medicine, knotweed has bitter and cool properties, and is associated with the Bladder meridian. It is taken internally to treat respiratory conditions such as bronchitis, cough, and inflammations of the mouth and throat, and has been approved by the German Commission E for those conditions. It is also used to treat certain skin disorders and parasites, and may help stop bleeding. Animal studies have shown that injections of knotweed decoctions can have a diuretic effect, which is more pronounced with increased dosages.

How much knotweed should I take?

The typical dose of knotweed is between 9 and 15 grams per day, taken internally as a decoction or powder. Concentrated extracts are also available; for a 5:1 extract, the recommended dose is 2-3 grams per day. Knotweed can also be ground into a tea for both internal and external applications.

What forms of knotweed are available?

Knotweed is available in pill, powder and decoction forms. Some herbal shops also sell concentrated knotweed extracts, which can be diluted in water.

What can happen if I take too much knotweed? Are there any interactions I should be aware of? What precautions should I take?

As of this writing, there are no known side-effects associated with knotweed, nor are there any known drug interactions with knotweed. However, it should be avoided by patients with spleen and stomach deficiencies, or patients with yin deficiency. As always, make sure to consult with a licensed health care provider before taking knotweed or any other herbal remedy or dietary supplement.


  • Editorial Committee of Chinese Materia Medica. State Drug Administration of China. Chinese Materia Medica. Shanghai Science and Technology Press, 1998.
  • Blumenthal M, Busse W, Goldberg A (eds.) The Complete German Commission E Monographs. Therapeutic Guide to Herbal Medicines. Boston; Integrative Medicine Communications, 1998, pp. 157-158.
  • Gruenwald J, Brendler T, Jaenicke C (eds.) PDR for Herbal Medicines. Montvale, NJ: Medical Economics Company, 2000, pp. 448-449.
  • Ke MQ. Physiochemical and Pharmacological Properties of Active Components of Chinese Materia Medica, 2nd ed. Hunan Science and Technology Press, 1982.
  • Wichtl M. Teedrogen, 4 aufl. Stuttgart: Verlagsges, 1997. In German.
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