Educational information, not medical advice — ask your doctor or midwife.
Sanguinaria is a folk plant name. On this page it means Polygonum aviculare, the sprawling roadside weed known in English as knotgrass. It is drunk as a tea for urinary trouble, loose stools and sore throats.
The name itself is the main hazard. In North America, "sanguinaria" usually means Sanguinaria canadensis, or bloodroot. Bloodroot is toxic, and salves made from it can eat away skin and flesh.
So always read the Latin name on a label. Polygonum aviculare is a mild food-grade weed. Sanguinaria canadensis is not, and the two are not swaps for each other.
Human evidence for knotgrass is very thin. Most of what is claimed comes from lab dishes, animals and long habit. Traditional use is not proof that a remedy works, and it is not proof that it is safe.
No one has shown how knotgrass acts in the human body, because the trials have not been done.
In test tubes, its flavonoids mop up free radicals (unstable molecules that can damage cells). Lab extracts also slow the growth of some bacteria and fungi. Whether any of that happens in a person drinking tea is unknown.
In animal studies, knotgrass extracts have shown a mild water-pill (diuretic) effect and some easing of swelling. The doses used were often far larger than a cup of tea. Animal results do not transfer to people on their own.
Its tannins bind protein and tighten tissue on contact. That is the likely basis for using it as a gargle or a skin wash. The effect is local and short, and it does not treat an infection.
Dried aerial parts (stems, leaves and flowers) are the usual form. They are sold loose or in tea bags.
Other forms you may meet:
Tinctures and liquid extracts made with alcohol.
Capsules and loose powder.
Mixed bladder or kidney teas, where knotgrass is one herb among several.
Gargles, mouth rinses and washes for small scrapes. These are folk preparations, not tested medicines.
Check the Latin name on the pack before you buy. It should read Polygonum aviculare. If it reads Sanguinaria canadensis, that is bloodroot, a different and toxic plant.
Knotgrass has a long folk record on both sides of the Atlantic.
Spanish and Portuguese settlers brought European herb lore to the Americas from the 1500s. Local healers folded knotgrass into their own practice. In Mexico, Central America and the Andes it was taken as a tea for urinary trouble and loose stools.
Healers also used it to slow bleeding. That is where the name sanguinaria came from, since sangre means blood. Village curanderos gave it for heavy periods and for sore, bleeding gums.
In Europe it had a parallel life. Writers from the Greek and Roman era onward listed it for coughs, wounds and bleeding. German regulators later allowed limited use for mild chest catarrh (a build-up of mucus), based on tradition rather than trials.
Stop and see a doctor if any of these happen:
Burning when you pass urine, fever, chills or pain in your back or side. These can mean a kidney infection.
Blood in your urine or stool.
Diarrhoea lasting more than two days, or any diarrhoea in a young child or an older adult.
Dizziness, fainting, muscle cramps or a thumping or irregular heartbeat (arrhythmia).
A spreading rash, swelling of the lips or face, or trouble breathing. Get urgent help for these.
Any symptom that has not improved within a week.
In the United States it is sold as a dietary supplement, which means no agency checks that it works. In the European Union and the United Kingdom it is sold as a herbal tea or food supplement. Germany's Commission E published a monograph allowing limited use for mild chest catarrh. In much of Latin America it is sold loose in markets with no checks on identity or purity.
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.
One email with the summary. We'll also send a short weekly evidence update — unsubscribe any time.
