Horsetail Supplements: Urinary Use, Silica Claims and Safety

What is horsetail?

Field horsetail (Equisetum arvense), sometimes called shavegrass, is a perennial plant with jointed stems and fine green branches. The medicinal herb is the green, sterile above-ground growth. The plant also produces a separate fertile shoot that releases spores. Its ancient relatives included tree-sized Calamites in Carboniferous forests more than 300 million years ago. Puget Sound Museum of Natural History^[1] · Missouri Department of Conservation field guide^[2]

People drink horsetail tea or take dry extracts for urinary complaints. Other products use it in hair supplements, nail coatings and skin ointments. The stems contain silica, a form of silicon, which contributes to their rough texture.

How was horsetail used historically?

In Natural History, Pliny the Elder records several plants that Greek writers called hippuris, a name associated with a horsetail-like appearance. He reports, with skepticism, that some authorities believed merely touching one of these plants could stop bleeding. He also describes juice used for nosebleeds, drinks for bladder or bowel complaints, and a different hippuris applied with vinegar to wounds. The translators’ notes show why these names demand care: for the last plant, one botanist suggested Ephedra fragilis and another suggested field horsetail. ^[3]

Huron H. Smith’s Ethnobotany of the Ojibwe Indians gives more precise identifications. He recorded the Pillager Ojibwe preparing a tea from the whole field horsetail for “dropsy,” an old term for swelling from fluid accumulation. The following entry identifies wood horsetail for kidney trouble as well as dropsy. For a household use, he describes handfuls of scouring rush, E. hyemale, used to scrub kettles and pans. The abrasive stems served as a cleaning tool, while the medicinal accounts name particular plants and preparations. ^[4]

In England, Gerard’s herbal describes a rough horsetail used to scour pewter and wooden kitchenware, explaining the household name “pewterwort.” Passage from Gerard’s herbal^[5]

European herbal medicine likewise distinguishes drinking from external use. The European Medicines Agency lists two traditional purposes for specified field-horsetail preparations: increasing urine flow as an aid for minor urinary complaints, and supporting care of superficial wounds. Its classification rests on longstanding use. ^[6]

Why do people take horsetail?

The clearest reason for the traditional urinary use and the modern “water pill” label is the same: under some conditions a named extract changes the balance between fluid consumed and urine passed. Symptom relief in a person with a urinary disorder is a more specific question. The beauty products have a different rationale, based largely on the silicon in the plant.

Forms of horsetail: species, teas and extracts

Field and marsh horsetail. A label should name Equisetum arvense and the green above-ground part. Marsh horsetail, E. palustre, can resemble it and contains alkaloids including palustrine. Animal toxicity has made species substitution a quality-control concern. A collection season or the name “shavegrass” alone cannot identify a powdered plant. Researchers have distinguished field and marsh horsetail using chemical profiles and DNA markers. ^[7]

A laboratory survey detected alkaloids characteristic of marsh horsetail in 26 of 34 products sold as medicinal horsetail. Those compounds indicated that marsh horsetail had entered the field-horsetail supply. In a separate brewing experiment using herb known to contain those compounds, about 42% passed into cold water and 60% into hot water. ^[8]

If an extract lists 7% silica by weight, 100 mg of that extract contains 7 mg of silica. Silica includes oxygen as well as silicon, so those 7 mg supply a smaller amount of elemental silicon. The percentage describes composition.

Common dosage

There is no nutritional daily requirement for horsetail. The US and Canadian dietary reference report also set no daily intake target for silicon because it lacked clear, consistent evidence of a nutritional requirement in people. National Academies dietary reference report^[9] A dried-herb tea and a concentrated capsule of equal weight can deliver different constituents.

For a tea traditionally used for minor urinary complaints, the European monograph describes 1–4 g of cut herb in 150 mL boiling water per preparation, with 3–12 g of herb as the daily range. These are directions for specified medicinal preparations in adolescents and adults. Measuring in grams avoids assuming every teaspoon holds the same weight. The monograph describes traditional use over two to four weeks and advises medical review if symptoms persist beyond one week, worsen, or are accompanied by fever, painful urination or blood in the urine. These are reasons to get assessed while symptoms are present. There is no established months-on, weeks-off cycle for continuing horsetail indefinitely. ^[6]

What do trials show about urine output, blood pressure and bladder symptoms?

Urine output over four days

Thirty-six healthy men received horsetail extract, hydrochlorothiazide (a prescription diuretic) and placebo during separate four-day periods. The men took 300 mg of dry extract three times daily (900 mg per day) during the horsetail period. The extract was standardized to 0.026% total flavonoids, the group of compounds used to keep its composition consistent. Researchers compared the recorded volume drunk with the volume of urine passed. With horsetail, the balance shifted toward more urine relative to intake compared with placebo. The group still drank more fluid than it excreted in urine. ^[10]

The study found no clear difference between horsetail and hydrochlorothiazide on its fluid-balance comparison. Four days and a small sample cannot establish that a supplement can replace a prescription diuretic. The measured sodium and potassium findings over that period also give little information about long-term use in someone with heart or kidney disease.

Blood pressure over three months

A three-month trial in 58 adults with stage I hypertension compared a 900 mg daily dry extract with 25 mg daily of hydrochlorothiazide. The researchers reported no clear difference between the two groups in how much blood pressure fell. The starting and ending pressures in the report do not reproduce its stated average decreases, leaving the size of the change uncertain. Both groups received an active treatment. ^[11]

Frequency of bladder symptoms with a three-herb blend

An eight-week trial tested a blend of horsetail, Crataeva bark and Lindera root in adults with overactive-bladder symptoms. Daytime and night-time urination were less frequent with the blend than with placebo. That trial’s question was symptom control with a specific mixture. It cannot identify which ingredient contributed. ^[12]

What has been tested for hair, nails and bone?

Silicon from a tea. In a small study in 12 healthy men, researchers measured silicon in blood and urine after specially prepared horsetail teas and low-silicon water. Silicon from the teas could be detected in the circulation and later in urine. The study measured exposure after drinking the tea. It did not measure how much hair grew, how often nails split or whether bones became stronger. ^[13]

Hair and nail products. A 90-day study in 60 women with thinning hair compared a commercial supplement with placebo. It found more terminal hairs, the thicker hairs counted in a defined scalp area, and less shedding with the supplement. Each tablet combined a marine protein complex, horsetail, acerola, biotin and zinc. The manufacturer funded the study. In a nine-month trial of 48 women with fine hair, hair strands lost less breaking strength with choline-stabilized orthosilicic acid than with placebo. That is a particular silicon compound rather than a field-horsetail extract. Those studies do not identify an effective horsetail dose for thicker hair. Combination hair trial^[14] · Silicon-compound trial^[15]

A local treatment provides another example. A 24-week nail psoriasis trial found better disease scores with a lacquer containing horsetail, a film-forming chitosan derivative and methylsulfonylmethane than with placebo. It tested a coating on psoriatic nails. Its findings cannot predict how often healthy nails will break after someone takes an oral capsule. ^[16]

Bone health. In cell culture, horsetail extract has affected the development of osteoclasts, the cells that break down bone. An older clinical report involved 122 postmenopausal women. Its initial phase included extract alone, placebo followed by extract, no treatment, and a product containing horsetail plus calcium. At one year the researchers assessed only women continuing active treatment. They reported a greater rise in vertebral bone density with horsetail plus calcium than with horsetail extract alone. That design leaves the contribution of horsetail to bone density uncertain, and it does not establish fracture prevention or faster fracture healing. Cell study^[17] · Clinical report^[18]

What about horsetail applied to wounds?

A trial in Iran compared a 3% field-horsetail ointment with a placebo ointment after an episiotomy, a surgical cut made during childbirth. Researchers assigned 108 women in equal groups. By days five and ten, the horsetail group had lower scores on a wound assessment that included redness, swelling and how well the wound edges met. At entry, the horsetail group had worse wound scores, and two women missed the last assessment. The result concerns a prepared ointment and a specific wound managed after delivery. ^[19]

Drawbacks and side effects

Vitamin B1. Horsetail can contain thiaminase, an enzyme that breaks down thiamine. The European assessment describes livestock poisoning from horsetail-containing feed and laboratory evidence of thiamine destruction. It also distinguishes heated or ethanol-extracted preparations, in which the enzyme is expected to be inactivated, from unheated powder. The assessment found no comparable neurological toxicity documented with traditional medicinal use in people. It gives no basis for assuming every capsule was heated, or for predicting a human deficiency after a particular number of days. The processing method and any test of the finished product determine what can be said about enzyme activity in a particular batch. ^[20]

Product contamination. A plant’s growing site and the part harvested matter. A study of E. arvense and another horsetail species growing on contaminated mine tailings found considerably less transfer of measured elements into shoots than into underground tissues. That field result cannot tell you the amount of lead, cadmium or arsenic in a retail capsule. Only tests of the actual batch can establish which metals were present and in what amounts. ^[21]

Medicines and electrolytes. If you take lithium, a prescription diuretic or blood-pressure medicine, ask your prescriber or pharmacist about the specific product before adding horsetail, and mention any fluid restriction. One lithium toxicity report involved several herbs including E. hyemale, not field horsetail alone. It cannot establish whether field horsetail affects how quickly the body removes lithium. A separate case of severe low sodium had several plausible causes, including low intake and inappropriate release of a water-retaining hormone. The authors considered horsetail a possible contributor. Short trial results and isolated cases give no reliable estimate of long-term potassium or sodium losses in supplement users. EMA interaction assessment, pages 33–34^[20] · Low-sodium case report^[22]

The bottom line

A short trial supports an effect on fluid balance with one field-horsetail extract. European traditional use covers minor urinary complaints, with limits on duration and specific reasons to seek care. Clinical research on a wound ointment and on combination hair or nail products is relevant to those preparations. It leaves an oral horsetail capsule’s value for hair growth, brittle nails and bone health uncertain.

The short-term urine result applies to the studied field-horsetail extract. If you have painful urination or unexplained swelling, seek medical assessment. If you take lithium or have been told to limit fluids, speak with your prescriber before using a medicinal horsetail product.

Source notes

The historical texts, agency monograph and clinical studies are linked alongside the relevant findings.

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