Educational information, not medical advice — ask your doctor or midwife.
Knotgrass is a low, sprawling weed of paths, yards and waste ground across Europe. The dried above-ground parts are brewed as a tea or made into extracts. In German-speaking countries it is called Vogelknöterich.
European folk use centred on coughs, sore throats and mild urinary complaints. The herb was also used as a drying wash on grazes and small cuts.
The plant is rich in tannins and in silica, a natural mineral. These are the traits old herbals pointed to when they explained its use.
Here is the honest verdict. Human evidence for knotgrass is very thin, and almost no controlled trials exist. Long use in a tradition is not proof that it works, and it is not proof that it is safe.
This page does not restate that point in every section. Take it as holding for every claim below that comes from folk use.
No one has shown in people how knotgrass works, or that it works at all.
The herb holds a lot of tannins. In test tubes, tannins bind proteins and leave a thin, drying film on tissue. That is the usual explanation for its old use as a gargle.
Lab work also finds flavonoids, a group of plant pigments. In cell and animal studies, these appear to damp down some signs of inflammation (swelling and irritation).
Silica from the plant dissolves into hot water. Older European writers linked this to lung and tissue health. That link has not been tested in people.
Some animal studies report a mild diuretic (water pill) effect, meaning more urine is passed. Small animal studies also hint at lower blood sugar. Neither finding has been confirmed in humans.
So the mechanism story is a laboratory story. Treat it as a reason someone might test knotgrass, not as proof of a benefit.
The most common form is loose dried herb for tea.
Other forms you may meet on shelves:
Tea bags, alone or in blends sold for coughs or for the urinary tract.
Tinctures and liquid extracts made with alcohol.
Dried, powdered herb in capsules or tablets.
A strong cooled brew used as a mouth gargle or a skin wash.
Knotgrass is rarely sold on its own in the United States. It turns up more often in German and Central European tea blends.
Check that the label prints the full plant name, Polygonum aviculare. Several unrelated weeds are also called knotweed or knotgrass.
Knotgrass has a long, well-recorded place in European folk medicine. It is best known in German-speaking regions as Vogelknöterich.
Herbals from the 1500s onward listed it for coughs, spitting of blood, loose bowels and bleeding wounds. Country healers brewed the dried herb or used it cold as a wash.
Its drying, puckering taste shaped its reputation. Writers grouped it with other astringent herbs used to tighten tissue and slow seeping.
Later German authors stressed the silica in the plant. They gave it for lung complaints and for general weakness after illness.
In the twentieth century, German expert reviewers allowed the dried herb for mild coughs and for mild soreness of the mouth and throat. That allowance rested on long use and a quiet safety record. It did not rest on clinical trials.
The herb also had non-medical roles. It was cut as fodder for geese and poultry, which is where the German name comes from.
Stop knotgrass and see a doctor if anything below applies.
Your cough lasts more than a week, or you get a fever or breathlessness.
You cough up blood, or you see blood in your urine.
Your sore throat is severe, one-sided, or you struggle to swallow.
Diarrhoea lasts more than two days, or you feel faint and dry.
You get burning on passing urine, back pain or a fever.
A wound turns red, hot, swollen or starts to ooze pus.
Go to emergency care for swelling of the lips, face or tongue, a spreading rash, or trouble breathing.
In Germany and much of the European Union, knotgrass is sold as a herbal tea and in traditional herbal medicines for mild coughs. In the United States, it is sold as a dietary supplement and is not approved as a drug for any illness.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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