Horsetail

In Western herbal medicine the dried sterile summer stem of Equisetum arvense is taken as an infusion or decoction, or applied to the skin ^{22,31Reference 22Bone · 2003A clinical guide to blending liquid herbs: Herbal formulations for the individual patientReference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. It is used as a diuretic and astringent for cystitis, urethritis, frequent urination, bedwetting in children, urinary gravel, blood in the urine, an enlarged prostate and prostatitis, and on the skin to speed wound healing and stop bleeding ^{22,31Reference 22Bone · 2003A clinical guide to blending liquid herbs: Herbal formulations for the individual patientReference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

The British Herbal Pharmacopoeia classes it as a genitourinary astringent and antihaemorrhagic, and topically as a vulnerary and styptic. It lists enuresis, prostatic disease and cystitis with blood in the urine ^{26,31Reference 26British Herbal Medicine Association · 1983British Herbal PharmacopoeiaReference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

Horsetail has appeared in European herbals since the 16th century. It fell out of use after the 18th century and was brought back into practice by Sebastian Kneipp in the 19th ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. German pharmaceutical texts record a wider range of uses: to clear water in kidney and bladder catarrh, to stop bleeding from the nose, stomach and lungs and heavy menstrual bleeding, for brittle nails and hair loss, and as a bath for rheumatic complaints, gout, slow-healing wounds and fractures ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

Germany’s Commission E approved it for post-traumatic and static oedema, for flushing the urinary tract in bacterial and inflammatory disorders and kidney gravel, and externally for slow-healing wounds ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. The European Medicines Agency recognises two traditional uses: increasing urine flow to flush the urinary tract in minor urinary complaints, and supportive treatment of superficial wounds ^{32Reference 32European Medicines Agency · 2016ReviewEuropean Union herbal monograph on Equisetum arvense L., herba (EMA/HMPC/278091/2015) — pharmacopoeial monograph. https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-equisetum-arvense-l-herba_en.pdfView study →}.

In Japan the fertile spring shoots are boiled and eaten, and field horsetail is used both as a medicine and as a cooking ingredient ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

In a double-blind, randomized crossover trial, 36 healthy men took a standardized dried extract of Equisetum arvense (900 mg/day), placebo (corn starch) or hydrochlorothiazide (25 mg/day) for four days each, with 10-day washouts between. The endpoint was 24-hour water balance ^{1Reference 1Carneiro et al. · 2014RCTRandomized, double-blind clinical trial to assess the acute diuretic effect of Equisetum arvense (field horsetail) in healthy volunteers — randomised controlled trialView study →}.

The extract produced a stronger diuretic effect than placebo, equivalent to hydrochlorothiazide, without significantly changing electrolyte excretion. Adverse events were rare and minor, and laboratory tests were unchanged ^{1Reference 1Carneiro et al. · 2014RCTRandomized, double-blind clinical trial to assess the acute diuretic effect of Equisetum arvense (field horsetail) in healthy volunteers — randomised controlled trialView study →}.

Gap: one small four-day trial in healthy men; no data on longer use, on people with urinary complaints, or on the tea.

A double-blind placebo-controlled trial applied a 3% E. arvense ointment to episiotomy wounds in 108 first-time mothers (54 per group). Healing was scored on the REEDA scale and pain on a visual analogue scale about 5 and 10 days after delivery ^{2Reference 2Asgharikhatooni et al. · 2015RCTThe effect of Equisetum arvense (horsetail) ointment on wound healing and pain intensity after episiotomy — randomised placebo-controlled trialView study →}.

Both healing and pain scores were significantly better in the horsetail group at both follow-ups ^{2Reference 2Asgharikhatooni et al. · 2015RCTThe effect of Equisetum arvense (horsetail) ointment on wound healing and pain intensity after episiotomy — randomised placebo-controlled trialView study →}.

Two rat studies, one in diabetic rats and one in healthy rats, found higher wound-closure ratios with 5–10% ointment than with no treatment or a petroleum jelly–lanolin base ^{3,4Reference 3Ozay et al. · 2013AnimalEffects of Equisetum arvense ointment on diabetic wound healing in rats — animal modelView study →Reference 4Ozay et al. · 2010AnimalEffects of Equisetum arvense ointment on dermal wound healing in rats — animal modelView study →}.

Gap: all the evidence is topical. The human trial is from a single centre and specific to episiotomy, and the rat studies used stronger ointments.

Ethyl-acetate and butanol fractions of the aerial parts showed strong DPPH and nitric-oxide radical scavenging, tracking their phenolic and flavonoid content. Isoquercitrin was the main flavonoid, the butanol fraction held a large amount of di-E-caffeoyl-meso-tartaric acid, and the water extract was weakest ^{5Reference 5Mimica-Dukić et al. · 2008In vitroPhenolic compounds in field horsetail (Equisetum arvense L.) as natural antioxidants — in vitroView study →}.

A comparison of five Serbian Equisetum species found E. telmateia, not E. arvense, had the highest antioxidant capacity. All the hydro-alcoholic extracts increased micronucleus formation at 62.5 µg/mL in vitro ^{6Reference 6Milovanović et al. · 2007In vitroAntioxidant, antimicrobial and genotoxicity screening of hydro-alcoholic extracts of five Serbian Equisetum species — in vitroView study →}.

A later study of four E. arvense extracts found no genotoxicity in human lymphocytes, and the ethanol–water extract protected against a known mutagen ^{7Reference 7Dormousoglou et al. · 2022In vitroInvestigation of the genotoxic, antigenotoxic and antioxidant profile of different extracts from Equisetum species — in vitroView study →}.

There is no human antioxidant data.

Injected into mice, a hydroalcoholic stem extract reduced acetic-acid writhing by 49–98% across 10–100 mg/kg, cut licking in the formalin test, and reduced carrageenan paw oedema by up to 30%. Naloxone did not reverse the pain relief, so it does not act through opioid receptors ^{8Reference 8Do Monte et al. · 2004AnimalAntinociceptive and anti-inflammatory properties of the hydroalcoholic extract of stems from Equisetum arvense in mice — animal modelView study →}.

A standardized extract inhibited human T-cell proliferation and lowered IL-2, IFN-γ and TNF-α in vitro ^{9Reference 9Gründemann et al. · 2014In vitroEquisetum arvense (common horsetail) modulates the function of inflammatory immunocompetent cells — in vitroView study →}.

A follow-up found the effect grew with the silica content of the decoction, and identified isoquercitrin as a second active compound ^{10Reference 10Steinborn et al. · 2018In vitroIn vitro anti-inflammatory effects of Equisetum arvense are not solely mediated by silica — in vitroView study →}. A 2023 study isolated nine compounds, several of which reduced inflammatory signalling in skin cells ^{11Reference 11Jeong et al. · 2023In vitroPhytochemical investigation of Equisetum arvense and evaluation of their anti-inflammatory potential — in vitroView study →}, and a 2025 rat ulcerative-colitis study found anti-inflammatory and antioxidant effects from oral and rectal extract ^{12Reference 12Koohi-Hosseinabadi et al. · 2025AnimalAntioxidant and anti-inflammatory effects of Equisetum arvense L. on acid-induced ulcerative colitis — animal modelView study →}.

No human trial exists, and the mouse doses were given by injection rather than by mouth.

Hydromethanolic extracts increased the growth and alkaline-phosphatase activity of human osteoblasts at 50–500 µg/mL, and harmed them at 1,000 µg/mL and above ^{13Reference 13Bessa Pereira et al. · 2012In vitroEquisetum arvense hydromethanolic extracts in bone tissue regeneration: in vitro osteoblastic modulation — in vitroView study →}.

In young Wistar rats, 120 mg/kg extract for 30 days increased jaw bone density ^{14Reference 14Arbabzadegan et al. · 2019AnimalEffect of Equisetum arvense extract on bone mineral density in Wistar rats via digital radiography — animal modelView study →}. Applied to the gums in a rat periodontitis model, extract reduced osteoclasts and bone loss through RANKL/OPG ^{15Reference 15Shiba et al. · 2022AnimalEquisetum arvense inhibits alveolar bone destruction in a rat model with lipopolysaccharide-induced periodontitis — animal modelView study →}.

Much of the wider case rests on silicon. An umbrella review of silicon-supplementation studies in animals found benefits to bone at around 139 mg Si/kg a day, an intake the authors judged unlikely to be reachable in humans ^{16Reference 16Pritchard et al. · 2024Systematic reviewSilicon supplementation for bone health: an umbrella review — systematic reviewView study →}.

Gap: no human trial of horsetail for bone, and the in-vitro benefit reverses to harm at high concentration.

Extracts of several Equisetum species inhibit bacteria in vitro. A 2018 study found E. arvense active only against gram-positive cocci ^{17Reference 17Pallag et al. · 2018In vitroEquisetum arvense L. extract induces antibacterial activity and modulates oxidative stress, inflammation — in vitroView study →}, and the five-species Serbian screen found most tested organisms sensitive to some degree ^{6Reference 6Milovanović et al. · 2007In vitroAntioxidant, antimicrobial and genotoxicity screening of hydro-alcoholic extracts of five Serbian Equisetum species — in vitroView study →}. Activity varies across species, solvents and strains.

Gap: no study has shown that oral horsetail reaches antibacterial levels in the urinary tract, and the common gram-negative urinary bacteria are poorly covered.

Methanol, n-hexane and dichloromethane extracts lowered blood glucose in streptozotocin-diabetic rats over five weeks ^{18Reference 18Safiyeh et al. · 2007AnimalAntidiabetic effect of Equisetum arvense L. (Equisetaceae) in streptozotocin-induced diabetes in male rats — animal modelView study →}. A later six-week study found moderate glucose lowering, improved insulin sensitivity at 100 mg/kg, and a trend toward higher SIRT1 in heart muscle ^{19Reference 19Hegedűs et al. · 2020AnimalSIRT1 activation by Equisetum arvense L. (horsetail) modulates insulin sensitivity in streptozotocin-diabetic rats — animal modelView study →}.

There is no human glucose data.

An ethanolic stem extract (50–100 mg/kg) increased open-arm time on the elevated plus maze in mice, comparable to diazepam and with less sedation ^{20Reference 20Singh et al. · 2011AnimalAnxiolytic effects of Equisetum arvense Linn. extracts in mice — animal modelView study →}.

In aged rats, a hydroalcoholic extract injected at 50 mg/kg as a long-term treatment improved memory in avoidance and water-maze tests ^{21Reference 21Guilherme dos Santos et al. · 2005AnimalCognitive enhancement in aged rats after chronic administration of Equisetum arvense L. with demonstrated antioxidant properties — animal modelView study →}.

The two studies measured different things, and neither has been repeated.

Short-term use. Horsetail is generally well tolerated in the short term. The four-day diuretic trial found no significant electrolyte or laboratory changes ^{1Reference 1Carneiro et al. · 2014RCTRandomized, double-blind clinical trial to assess the acute diuretic effect of Equisetum arvense (field horsetail) in healthy volunteers — randomised controlled trialView study →}. Mild stomach complaints and allergic reactions, such as rash or facial swelling, have been reported ^{32Reference 32European Medicines Agency · 2016ReviewEuropean Union herbal monograph on Equisetum arvense L., herba (EMA/HMPC/278091/2015) — pharmacopoeial monograph. https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-equisetum-arvense-l-herba_en.pdfView study →}.

Marsh horsetail contamination. The alkaloids palustrine and palustridiene belong to marsh horsetail (Equisetum palustre), which is poisonous to livestock ^{30,31Reference 30Cramer et al. · 2015Structural and quantitative analysis of Equisetum alkaloids — analyticalView study →Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. The two species look alike and grow together, so dried horsetail often reaches the shelf contaminated. An analysis of 34 products from pharmacies, drug stores, supermarkets and web stores found 26 positive for E. palustre alkaloids, at 0.29–21.7 mg/kg. Between 42% (cold water) and 60% (hot water) of the alkaloids passed into the tea ^{29Reference 29Nowak et al. · 2022Biomarker-based determination of Equiseti herba contamination by Equisetum palustre using HPLC-MS/MS — analyticalView study →}. The European Pharmacopoeia includes a test to exclude E. palustre, and the European Medicines Agency advises buying quality-controlled horsetail ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

Thiaminase. Horsetail contains thiaminase, an enzyme that breaks down vitamin B1. Horses fed horsetail-contaminated hay develop a thiamine-deficiency disease that responds to thiamine injections ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. The enzyme is present in the fresh and dried plant, but it is destroyed by heating to 80 °C, and none was found in commercial water extracts or in a 30% alcohol extract ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. No thiamine deficiency from traditional use has been seen in people ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}. Raw, unheated powder may still carry the active enzyme, so long-term use of the powder is best avoided ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

Nicotine. Horsetail contains trace nicotine. A man with a history of allergic reactions to the nicotine in tobacco smoke developed a seborrhoeic-dermatitis-like rash on his hands and face from handling horsetail ^{23,31Reference 23Sudan · 1985Case reportSeborrhoeic dermatitis induced by nicotine of horsetails (Equisetum arvense L.) — case reportView study →Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

Fluid and potassium. Do not use horsetail to increase urine flow where reduced fluid intake is advised, such as in severe heart or kidney disease ^{32Reference 32European Medicines Agency · 2016ReviewEuropean Union herbal monograph on Equisetum arvense L., herba (EMA/HMPC/278091/2015) — pharmacopoeial monograph. https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-equisetum-arvense-l-herba_en.pdfView study →}. Horsetail is rich in potassium, and people whose kidneys handle potassium poorly should use it with care ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

Lithium. A woman on lithium developed lithium toxicity after two to three weeks of a diuretic herbal mixture that included a related horsetail, E. hyemale. Diuretic herbs may raise lithium levels through dehydration ^{31Reference 31European Medicines Agency · 2016Assessment report on Equisetum arvense L., herba (EMA/HMPC/278089/2015) — pharmacopoeial assessment. https://www.ema.europa.eu/en/documents/herbal-report/final-assessment-report-equisetum-arvense-l-herba_en.pdfView study →}.

HIV medicines. Two people stable for years on efavirenz-based HIV treatment lost control of the virus after adding a horsetail supplement, and the authors advised avoiding the combination until more is known ^{36Reference 36Cordova et al. · 2017Case reportPossible Drug-Herb Interaction between Herbal Supplement Containing Horsetail (Equisetum arvense) and Antiretroviral Drugs — case reportsView study →}. The cause was not established, and no pharmacokinetic study has tested it.

Drug metabolism. In human liver cells, a horsetail infusion raised the expression of the gene for CYP3A4, an enzyme that clears many drugs, but did not change the activity of the drug pump P-glycoprotein ^{37Reference 37Mazzari et al. · 2022In vitroIn vitro effects of European and Latin-American medicinal plants in CYP3A4 gene expression, glutathione levels, and P-glycoprotein activity — in vitroView study →}. This has not been tested in people.

Children. Use under 12 years is not recommended, for lack of data ^{32Reference 32European Medicines Agency · 2016ReviewEuropean Union herbal monograph on Equisetum arvense L., herba (EMA/HMPC/278091/2015) — pharmacopoeial monograph. https://www.ema.europa.eu/en/documents/herbal-monograph/final-european-union-herbal-monograph-equisetum-arvense-l-herba_en.pdfView study →}.