Benefits
Traditional German astringent tea for short-lived loose stools
Germany's former Commission E listed silverweed herb, taken by mouth, for mild, nonspecific acute diarrhea, and German pharmacy guidance describes it as supportive for that use. This rests on long-standing use and the herb's tannin content, not on trials in people. Loose stools that persist, keep returning, or come with blood or fever need medical care.
Traditional use for mild discomfort during menstruation
The same German monograph listed silverweed for mild menstrual discomfort, and one German nickname for it translates as cramp herb. A German pharmacy article calls the modern data on the herb inconsistent and its old cramp herb reputation overrated, and animal experiments on isolated uterus tissue found it raised muscle tone and contraction frequency rather than relaxing it. No human trial has tested this use.
Ellagitannins led by agrimoniin, plus flavonoids
In 12 batches of Siberian silverweed herb, agrimoniin ranged from about 18 to 57 mg per gram depending on the region, with the highest level in the leaves (61 mg/g). Three further ellagitannins, potentillin and agrimonic acids A and B, were identified alongside flavonoid glucuronides. Tannin levels vary widely between harvests and growing regions.
Tannins converted to urolithins by gut bacteria in lab tests
When a water extract of silverweed herb was incubated with human stool samples, gut bacteria formed urolithins A, B and C, as they did with tormentil and other ellagitannin-rich plants. These urolithins lowered release of the inflammatory signal TNF-alpha from human immune cells grown in the lab. No study has measured this in people taking silverweed.
Effects on human colon lining cells in lab tests
Water extracts of the aerial parts of silverweed and four related plants were added to cultured human colon cells. All scavenged free radicals in a concentration-dependent way, lowered IL-6 output from colon connective tissue cells at lower concentrations and changed the cell skeleton; in a membrane test, silverweed also disturbed the epithelial cells. Cell-culture work only.
Mechanism of action
Astringent tannin content
Tannins are the basis of silverweed's traditional astringent use. Reference texts give 5 to 10% tannins in the dried herb, mainly ellagitannins, though a Polish analysis cited in a lab study found under 1% in the leaves by another method, and one reference work calls its astringent effect rather weak compared with other tannin herbs. The astringent action has not been measured in people taking silverweed.
Gut bacteria turn ellagitannins into urolithins
Human gut bacteria break the ellagitannins of silverweed herb into smaller compounds called urolithins, which have their own anti-inflammatory activity in lab cells. Any effect of the tea may therefore depend partly on a person's gut bacteria, but this has not been studied in people.
Preparation changes which compounds are delivered
In one analysis, agrimoniin made up about 9 to 11% of the measured phenolic compounds in silverweed teas (infusion and decoction) but about 41 to 48% in alcohol-based liquid extracts and tinctures, likely because water extracts ellagitannins poorly and heat can break them down. A tea and a tincture are therefore not chemically equivalent.
Clinical trials
Ex vivo study incubating water extracts of ellagitannin-rich plant materials, including silverweed herb and tormentil rhizome, with human stool samples, then testing the urolithins formed on human macrophage-like immune cells (THP-1 line). (Piwowarski et al. 2014, J Ethnopharmacol)
Human fecal samples and a human immune cell line; no one took silverweed by mouth.
Gut bacteria formed urolithins A, B and C from all the plant extracts tested, including silverweed. All urolithins significantly inhibited TNF-alpha production; urolithin A was the most potent (29.2% inhibition at 0.625 micromolar), and only urolithin C lowered IL-6. Whether enough urolithins form after drinking silverweed tea to matter is unknown.
Cell-culture study of aqueous extracts from the aerial parts of P. argentea, P. anserina, P. grandiflora, P. erecta and Drymocallis rupestris at 25 to 250 micrograms/ml on normal human colon epithelial cells (CCD 841 CoTr) and myofibroblasts (CCD-18Co). (Paduch et al. 2015, Curr Drug Targets)
Two human colon cell lines; no one took silverweed by mouth.
All extracts showed similar concentration-dependent free radical scavenging. Extracts, especially at lower concentrations, decreased IL-6 production by myofibroblasts but not by epithelial cells, and altered the actin cell skeleton. In a membrane-integrity test, silverweed, like two of the other plants, strongly disturbed epithelial cell membranes. These are cell-culture results and do not show effects in the human gut.
Lab mutagenicity study comparing self-prepared ethanolic and aqueous extracts and commercial tinctures of Alchemilla species and silverweed herb, using 2-nitrofluorene as the standard mutagen, with and without the tannin fraction. (Schimmer et al. 1995, Planta Med)
Laboratory test system; no human or animal intake.
All samples showed weak or moderate inhibition of mutagenicity. Total tannin content did not correlate well with the degree of inhibition, but tannin-free extracts showed no inhibition, so the tannins contributed at least partly. A test-tube result like this says nothing about cancer risk in people.
Short lab report testing aqueous extracts of the aerial parts of nine Potentilla species, including silverweed, for antibacterial and antifungal activity. (Tomczyk et al. 2008, Fitoterapia)
Bacterial and fungal cultures; no human or animal intake.
The extracts showed their strongest antimicrobial activity against Helicobacter pylori, with minimum inhibitory concentrations of 0.1 and 0.5 mg/ml. The abstract does not give separate results for silverweed, and activity in a culture dish does not show any effect after drinking the tea.
Non-interventional, open, multicenter observational study in outpatient practice with no control group; patients took Gastritol Liquid, an alcohol-based combination of chamomile, silverweed, licorice, angelica, blessed thistle and wormwood extracts, for 2 weeks. The second author is from the product's registration holder, Dr. Gustav Klein. (Wegener et al. 2016, Phytother Res)
149 outpatients with mild digestive complaints, 90 without and 59 with diabetes. The abstract does not state the dose used; the product's prescribing information gives 30 drops three times daily, with silverweed the largest of the six extracts.
Symptoms improved over 2 weeks in both groups, most for vomiting (down 66.7%, and 63.9% in those with diabetes) and retching (down 52.2% and 53.6%), and about 90% rated an overall improvement. Seven patients reported mild adverse events, mostly short-lived nausea. With no control group and six herbs combined, none of this can be attributed to silverweed.