Educational information, not medical advice — ask your doctor or midwife.
Loosestrife (Lythrum salicaria), often called purple loosestrife, is a tall pink-flowered marsh plant. The dried flowering tops are used as a folk remedy for loose stools, and as a wash for minor wounds, sore mouths and irritated eyes. It is sold as a dried herb for tea, and sometimes as a tincture (an alcohol extract).
The short verdict on evidence: we could not find human trials of this plant, so its uses rest on long folk habit, not on proof. Traditional use tells you that people have relied on a plant for a long time. It does not tell you that the plant works, and this is the only place in this page we will say so.
One naming point matters. Purple loosestrife is not the same plant as yellow loosestrife (Lysimachia species), and the two are often mixed up in old books and on labels. Check the Latin name on any product you buy.
The plant is rich in tannins, which are plant compounds that make tissue feel tight and dry. In a test tube, tannins bind protein and can slow the leak of fluid from irritated surfaces. That is the usual reason given for its old use in diarrhoea and as a skin wash.
Lab work also shows that loosestrife extracts can slow the growth of some bacteria and fungi, and can mop up free radicals (unstable particles that damage cells).
None of this has been tested in people. A compound that acts on cells in a dish may do nothing useful once you swallow it, so treat these ideas as untested theory.
You will most often find these forms:
Dried flowering tops, loose or in tea bags, for a hot infusion.
Tincture, an alcohol extract taken by the drop.
A cooled, strained tea used on the skin as a wash or compress.
A rinse or gargle for the mouth.
Standardised extracts and capsules are uncommon. Because strength is not controlled, you cannot assume one brand matches another.
Loosestrife has a long record in European folk medicine, from Ireland and Britain across to central and eastern Europe. Old herbals list it for dysentery (severe bloody diarrhoea) and for stubborn loose stools, and it was a staple in some rural households during outbreaks.
It was also used outwardly: as a wash for cuts and leg ulcers, a gargle for sore throats, and an eye bath. Modern German and French herbal lists still name it for mild diarrhoea, based on this history rather than on trials.
See a doctor if diarrhoea lasts more than two days, or if it comes back again and again.
Get urgent care if you see blood or black colour in your stool, if you have severe stomach pain, a high fever, or signs of dehydration such as dizziness, very little urine or a dry mouth that will not settle.
Also see a doctor if a wound looks redder, hotter or more swollen after you use a wash on it, if a mouth sore does not heal within two weeks, or if your eyes become red or painful.
Stop and get advice if you take regular medicine and it seems to work less well after you start this herb.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
Reviewed by the HealisticMD editorial team How we grade evidence →
The published evidence for Loosestrife is weak or absent. That usually means no controlled trial has tested it, not that a trial found it ineffective — the two are different, and we grade only what has been published.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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