cola de caballo

Horsetail (Equisetum arvense L.): A Comprehensive Reference

1. Identity, Taxonomy, and Botanical Description

Equisetum arvense, commonly known as field horsetail or common horsetail, is a species of vascular plant in the horsetail family Equisetaceae. Like all horsetails, it is a type of fern, and it is native throughout the arctic and temperate regions of the Northern Hemisphere. The species is known by the common name of "horsetail" in English-speaking countries, "cola de caballo" in Spanish-speaking countries, "prêle des champs" in France, "ackerschachtelhalm" in Germany, "tsukushi" in Japan, and "cavalinha" in Brazil.

The name Equisetum is derived from the Latin roots equus, meaning "horse," and seta, meaning "bristle." It goes by several names including Field Horsetail, Snake Grass, Devil's Guts, Horsetail Fern, Pinegrass, Meadow Pine, Foxtail Rush, and Marestail.

Equisetum arvense is a perennial herbaceous plant that spreads by means of an underground rhizome. The slender, felted rhizome freely forks and bears stem tubers. The species is dimorphic, exhibiting two distinct growth forms, both arising from the same rhizome. It consists of two types of stems — sterile, non-reproductive and photosynthetic, and reproductive and non-photosynthetic. The latter, 10 to 25 centimeters long with brown scale leaves and a 10 to 40 millimeters long spore cone, emerge in spring then wither and give way to the sterile, photosynthetic stems. The sterile green stems are around 20 to 80 cm, erect or decumbent, slightly rough, with 6 to 18 vertical ridges or sections.

Horsetail is derived from huge, tree-like plants that thrived 400 million years ago during the Paleozoic era. The Equisetum genus, Equisetaceae family, is widely distributed worldwide and may be the oldest nonextinct genus on Earth, with about 30 known species.

Common Preparations and Forms

In traditional Austrian herbal medicine, horsetail has been used internally as tea, or externally as baths or compresses, for treatment of disorders of the skin, locomotor system, kidneys and urinary tract, and rheumatism. Recognized herbal preparations include comminuted herbal substance; expressed juice (1:1.6–2.0); liquid extracts with various solvent ratios (ethanol 31.5%, ethanol 96%/water/sweet wine); and dry extracts (drug:extract ratios of 4–7:1 with water, or 7.5–10.5:1 with ethanol 70%). The pharmaceutical form may be a herbal preparation in solid or liquid dosage forms or as a herbal tea for oral use.

By definition, the herbal drug consists of whole or cut, dried sterile aerial parts of Equisetum arvense L., with main characteristic constituents including flavonoids, silica, caffeic acid esters, styryl pyrone glucosides, sterols, essential oil, and thiaminase.

2. Traditional and Historical Use

Horsetail (Equisetum arvense) is an herbal remedy that dates back to ancient Roman and Greek times, and was used traditionally to stop bleeding, heal ulcers and wounds, and treat tuberculosis and kidney problems. Reportedly first recommended by the Roman physician Galen, several cultures have employed horsetail as a folk remedy for kidney and bladder troubles, arthritis, bleeding ulcers, and tuberculosis.

In the second century AD, the Greek physician and philosopher Galen recommended Horsetail for treating arthritis, kidney, and bladder issues. In the 1st century CE, the Greek Dioscorides described the plant — called hippouris in ancient Greek — and its uses in his vast encyclopedia.

In Madaus' vast compilation of traditional therapeutic uses of plants published in 1938 (Lehrbuch der biologischen Heilmittel), Equisetum is described as the agent par excellence for the treatment of tuberculosis (even with internal hemorrhages) and kidney pathologies. Its astringent action is clearly stated and recommended to stop all kinds of wounds, and to treat diarrhea.

Equisetum arvense has a long history of cultural use with Native Americans and ancient Roman and Chinese physicians using it to treat a variety of ailments. Native Americans praised its antimicrobial, diuretic, wound healing, and general health-promoting qualities. In traditional Chinese medicine, Horsetail is valued for its ability to reduce fever and treat eye inflammation as well as dysentery, flu, swelling, and hemorrhoids.

E. arvense has a history of traditional medicinal use for the treatment of various illnesses, including bladder disorders and tuberculosis. It is additionally employed as a hemostatic agent to manage excessive menstruation, as well as pulmonary, gastric, and nasal hemorrhages.

The 17th century English herbalist Culpeper wrote that horsetail "is very powerful to stop bleeding in or outward… including ulcers and inflammations."

For a long time, E. arvense has been used in traditional medicines for the treatment of brittle fingernails, loss of hair, and rheumatic diseases.

Apart from its use in medicine, the stems were used extensively for their abrasive properties, including being used to remove resin buildup from the wheels used to play the hurdy-gurdy. They were used in historical times for scouring pots and polishing pewter and were commonly called "scouring rushes."

3. Key Constituents and Active Compounds

The aerial parts of Equisetum arvense contain flavonoids, saponins, caffeic acid, phenolic compounds, alkaloids, sterols, and minerals (primarily silicon and potassium salts). Previous studies revealed that E. arvense contains alkaloids, carbohydrates, proteins and amino acids, phytosterols, saponins, sterols, ascorbic acid, silicic acid, phenol, tannin, flavonoids, triterpenoids, volatile oils, and many other biologically active constituents.

Silica (Silicon Compounds)

Since E. arvense is the terrestrial plant with the highest concentration of silicates (5–8% of the dry herb), calcium, potassium, and other minerals, it is traditionally used to prevent osteoporosis around the world, and it is mentioned in the European Pharmacopoeia for its ability to increase bone and cartilage formation and strengthen bones. Analysis of E. arvense has confirmed that the Equisetaceae is rich in silica, potassium, calcium, manganese, and phosphorus.

The enzyme thiaminase (which breaks down vitamin B1) also occurs in Equisetum arvense. A high presence of thiaminase in the fresh and dried plant could be shown by Fabre et al. (1993). The thermo-labile enzyme was inactivated totally at 80°C, and the temperature for 50% denaturation was near 70°C.

Flavonoids

Apigenin, luteolin, equisetumoside A, equisetumoside B, and equisetumoside C, nicotine, palustrine, and palustrinine are phytochemical compounds reported from this plant. Isolated secondary metabolites include kaempferol 3,7-di-O-β-D-glucopyranoside, icariside B2, luteolin 5-O-β-D-glucopyranoside, 4-O-β-D-glucopyranosyl caffeic acid, 4-O-caffeoylshikimic acid, and 3-O-caffeoylshikimic acid, among others.

Quercetin and dicaffeoyltartaric acid (chicoric acid) are the main constituents of Equisetum arvense. The identified compounds, including hydroxycinnamic acids, hydroxybenzoic acids, flavonoids, and stilbenes, have been associated with various bioactivities. Flavonoids and hydroxycinnamic acids are known for their antioxidant properties.

Whether flavonoids or phenolic acids are the predominant compounds in E. arvense extracts depends on the extractant used. In one publication, flavonoids were the main compounds in ethyl acetate and butanol extracts, while phenolic acids were the major constituents in aqueous extracts.

Other Constituents

Equisetum arvense has a highly complex pattern of phenolic compounds, namely various flavonoids, phenolic acids, and phytosterols. Silica helps in the absorption and use of calcium and also in the formation of collagen. Secondary metabolites such as flavonoids (quercetin, kaempferol, luteolin, and apigenin) and triterpenoids (oleanolic acid, betulinic acid, and ursolic acid) have also been identified.

4. Mechanisms of Action

Diuretic Action

The presence of high concentrations of flavonoids, phenolic compounds, and mineral salts indicates a mild diuretic action of this herbal medicine. The horsetail plant exerts slight diuretic activity, possibly due to the high concentrations of flavonoids, phenolic compounds, and mineral salts found in the aerial parts of E. arvense.

Bone and Connective Tissue Effects

Silica has been reported to promote collagen synthesis and help bone mineralization. The abundance of silicon salts indicates that Equisetum arvense may possess remineralization properties. Equisetum arvense has high silica content, and its extract has been evaluated for silicon concentration in relation to osteoblast induction.

Anti-inflammatory and Antioxidant Action

E. arvense has been shown to have antibacterial, antifungal, antioxidant, analgesic, anti-inflammatory, antidiabetic, antitumor, cytotoxic, and anticonvulsant activities. Equisetum arvense preparations have been reported to be diuretic, antioxidant, vasorelaxant, antinociceptive, anti-inflammatory, haemostatic, and sedative.

5. Scientific Evidence by Area of Use

5.1 Diuretic Effects

Clinical evidence (moderate, limited to small trials):

One key study assessed the diuretic action and the short-term safety of a standardized dry extract of the aerial parts of E. arvense in healthy men using a randomized, double-blind clinical study. The effects on fluid balance and urinary catabolite excretion, as well as possible toxic effects on liver, kidney, and heart function, were assessed. The drug effects were compared to those of a placebo (corn starch) and a classic diuretic (hydrochlorothiazide).

In this double-blind, randomized clinical trial, 36 healthy male volunteers were randomly distributed into three groups (n = 12) that underwent a three-step treatment. For four consecutive days, the researchers alternately administered a standardized dried extract of Equisetum arvense (EADE, 900 mg/day), placebo (corn starch, 900 mg/day), or hydrochlorothiazide (25 mg/day), separated by a 10-day washout period. Each volunteer served as his own control.

Intergroup comparisons of fluid balances revealed significant differences between the E. arvense group and placebo (P < 0.001) and between the hydrochlorothiazide group and placebo (P = 0.026). However, no significant difference between the E. arvense and hydrochlorothiazide groups was observed (P = 0.566). These results demonstrate that E. arvense and hydrochlorothiazide were associated with similar diuretic effects that were both superior to placebo. The E. arvense extract produced a diuretic effect that was stronger than the negative control and was equivalent to that of hydrochlorothiazide without causing significant changes in the elimination of electrolytes. There was no significant increase in the urinary elimination of catabolites, and rare minor adverse events were reported.

The evidence base for diuretic use rests on Carneiro 2014 and Faustino 2022, both from the same Brazilian research network. Newer Equisetum publications since 2022 focus on phytochemistry, anti-inflammatory activity, and dermatological applications. No independent diuretic replication trial has been published, which remains the single biggest gap in the clinical literature.

Regulatory status: The German Commission E approved the use of Equisetum arvense for the treatment of posttraumatic and static edema and as a diuretic for bacterial and inflammatory diseases of the urinary tract presenting with urinary sediment. However, E. arvense does not satisfy the requirements as a well-established medicine, despite an ancient tradition of use, because clinical studies of its effects on renal function and safety are lacking. The European Medicines Agency concluded that clinical data on the absorption, distribution, and pharmacokinetics of Equisetum arvense are scarce or completely lacking.

The ESCOP therapeutic indications include irrigation of the urinary tract, especially in cases of inflammation and renal gravel, as an adjuvant in the treatment of bacterial infections of the urinary tract, and topically as a wound healing agent.

5.2 Antihypertensive Effects

Clinical evidence (preliminary; single trial):

An aerial part extract of E. arvense demonstrated antihypertensive effect by promoting a decrease in systolic blood pressure by 12.6 mmHg and diastolic blood pressure by 8.1 mmHg, respectively, in a double-blind randomized clinical trial carried out among 58 systemic arterial hypertension patients (stage I) (Carneiro et al., 2022). Significant decreases in systolic and diastolic blood pressure were reported for the E. arvense-treated group, with no significant differences found between the hydrochlorothiazide and E. arvense efficacy, and only minor and rare adverse effects were recorded.

Although E. arvense is used as a diuretic agent worldwide and regulated by the European Medicine Agency (EMA) and Brazilian National Health Surveillance Agency (ANVISA), few studies evaluating its efficacy and safety have been published and no prior clinical trial assessing its antihypertensive effect had been reported before this study. The evidence in this area must be considered preliminary, as it derives from a single, small trial by the same research network responsible for the diuretic trial.

5.3 Bone Health and Osteoporosis

Evidence: primarily preclinical and in vitro; clinical evidence weak.

Equisetum arvense is suggested for the treatment of osteoporosis because of its very high silica content in the whole plant kingdom. E. arvense preparations are claimed to have beneficial effects on bone disorders and to promote bone healing after bone surgery or fracture.

Silicon's role in bone metabolism has been studied in relation to horsetail; the sterile stems are used as medicines in various countries, constituting 'Equiseti herba' of European Pharmacopoeias.

Scientific evidence is not sufficient to declare E. arvense as bone-protecting in clinical practice, and the role of E. arvense in muscle homeostasis and sarcopenia has not been thoroughly investigated. Thus, while mechanistic rationale exists, bone health claims remain unsupported by robust human clinical trials.

5.4 Overactive Bladder and Urinary Incontinence

Evidence: one positive Phase 2 trial, but using a multi-herb combination.

A phase 2, randomised, double-blind, placebo-controlled trial evaluated Urox, containing concentrated extracts of Crataeva nurvala stem bark, Equisetum arvense stem, and Lindera aggregata root, in the treatment of symptoms of overactive bladder and urinary incontinence.

One hundred and fifty participants (59% female, mean age 63.5 years) took part in the study. At week 8, urinary day frequency was significantly lower in response to treatment (7.69/day) compared to placebo (10.95/day; p < 0.001). Episodes of nocturia were significantly fewer after 8 weeks of treatment (2.16/night) versus placebo (3.14/night). Symptoms of urgency and total incontinence were also significantly lower (all p < 0.01) in the treatment group. Significant improvements in quality of life were reported after treatment in comparison to placebo, and no significant side effects were observed resulting in withdrawal.

Although horsetail shows some promise for the treatment of overactive bladder, there are no clinical data demonstrating this efficacy from horsetail alone. The above trial cannot be attributed specifically to E. arvense because it tested a combination product.

5.5 Wound Healing

Evidence: limited clinical data; supported by traditional use and Commission E approval.

Topical use as an adjuvant for the treatment of wounds that exhibit difficult healing has been reported. Controlled clinical studies with equisetum stem extract have demonstrated its diuretic and wound healing activity in patients. One clinical trial analyzed the wound-healing effect of a 3% E. arvense ointment. These findings remain limited in scope and independent replication is lacking.

5.6 Nail and Hair Health

Evidence: preliminary; small clinical studies.

Scientific research confirms that Equisetum arvense is rich in organic silica, including a report published in the Journal of Plastic Dermatology that encompassed two clinical trials. One clinical trial combined horsetail with a sulfur donor in a water-alcohol solution, applied nightly for 28 days to the nails of 36 women with nail plate alterations. The researchers observed a significant decrease in longitudinal grooves as well as an 85 percent reduction in patients reporting lamellar splitting of treated nails. These findings require replication in larger, independent trials before strong conclusions can be drawn.

5.7 Anti-inflammatory and Dermatological Effects

Evidence: primarily in vitro; limited human data.

Extracts of E. arvense have been used in traditional medicine, particularly for the treatment of inflammatory disorders; research has aimed to determine the phytochemical compounds in E. arvense ethanolic extract and their anti-inflammatory properties. Pharmacological studies have unveiled additional medicinal uses of E. arvense, such as its role as an anti-inflammatory and antioxidant agent. However, the bulk of this evidence remains in vitro or in preclinical animal models.

5.8 Antidiabetic, Antimicrobial, and Other Pharmacological Properties

Evidence: preclinical only.

Preclinical studies have revealed various pharmacological actions of Equisetum arvense, including antioxidant and antidiabetic properties, but no acute hepatotoxicity. The most relevant reported pharmacological effects include antioxidant, anticarcinogenic, antimicrobial, vascular and ileum smooth muscle relaxant, analgesic, anti-inflammatory, antinociceptive, cytotoxic, antidiabetic, hepatoprotective, antilithiatic, dermatologic, and wound healing activities. None of these properties have been confirmed in robust human clinical trials.

6. Body Systems and Health Areas

• Urinary/Renal System: The most widespread traditional use of Equisetum is as a diuretic, followed by the treatment of genitourinary diseases (kidney diseases, urethritis, kidney stones, and others).
• Cardiovascular System: Preliminary clinical evidence suggests antihypertensive activity comparable to low-dose hydrochlorothiazide, but this is based on a single small trial.
• Skeletal/Connective Tissue: Silica helps in the absorption and use of calcium and also in the formation of collagen, providing a mechanistic basis for use in bone and connective tissue health, though clinical evidence is lacking.
• Skin, Hair, and Nails: Horsetail is used in skin, hair, and nail care products, thanks to its rich silica content.
• Inflammatory Conditions: Extracts of E. arvense have been used in traditional medicine for the treatment of inflammatory disorders.
• Hemostasis: It is employed as a hemostatic agent to manage excessive menstruation, as well as pulmonary, gastric, and nasal hemorrhages.

7. Dosage Forms and Dosages Reported in Studies and Monographs

The British Herbal Pharmacopoeia lists dried herb, or infusion or decoction of the dried herb at a single dosage of 1–4 g three times daily; liquid extract (1:1) in 25% alcohol at a single dosage of 1–4 ml three times daily, with indications including enuresis, prostatic disease, cystitis with haematuria, and urethritis.

In the key diuretic clinical trial: 36 healthy male volunteers underwent a three-step treatment in which the researchers administered a standardized dried extract of Equisetum arvense (EADE) at 900 mg/day, placebo (corn starch) at 900 mg/day, or hydrochlorothiazide at 25 mg/day for four consecutive days, separated by 10-day washout periods.

In the antihypertensive trial: The study was carried out among 58 systemic arterial hypertension patients (stage I) using an aerial part extract of E. arvense.

The EMA Community Herbal Monograph identifies approved herbal preparations including dry extract (4–7:1, extraction solvent water) and dry extract (7.5–10.5:1, extraction solvent ethanol 70%), among multiple other liquid extract forms.

In the overactive bladder trial: One hundred and fifty participants were treated for 8 weeks with a combination product (Urox) containing Equisetum arvense stem extract alongside other botanical extracts.

One study used a standardized dried extract of Equisetum arvense L. with a minimum 10% (w/w) silica content established by thin-layer chromatography (TLC).

8. Safety Considerations and Interactions

Thiaminase and Vitamin B1 Depletion

A high presence of thiaminase (an enzyme that degrades vitamin B1) in the fresh and dried plant has been demonstrated. This thermo-labile enzyme was inactivated totally at 80°C, and the temperature for 50% denaturation was near 70°C. This has led to concern about potential thiamine depletion with prolonged or high-dose use of unprocessed or inadequately heated preparations. Horsetail side effects include thiamine depletion and lithium toxicity risk.

Pregnancy and Lactation

Remedies containing E. arvense are not recommended during pregnancy or breastfeeding since little information is available on their safety.

Species Confusion

Horsetail can be easily mixed up with other horsetail species. In particular, Equisetum arvense can be confused with Equisetum palustre, which is potentially toxic.

Toxicity Studies

A 13-week rat toxicity study evaluated E. arvense in the diet at doses of 0, 0.3, 1, and 3%. The dosage selections were based on an estimated intake for humans of approximately 5 mg/kg daily. No toxicity was detected related to clinical signs, body weight, urinalysis, hematology, serum biochemistry data, organ weights, or histopathological findings.

In the key human diuretic trial, no changes in electrolytes or liver, kidney, or hematological function tests were observed, and adverse reactions were mild and infrequent.

Allergic Reactions

Allergic reactions (e.g., rash, swelling of the face) may occur. No case of overdose has been reported.

Regulatory Status

The German Commission E approved the use of Equisetum arvense for the treatment of posttraumatic and static edema and as a diuretic for bacterial and inflammatory diseases of the urinary tract presenting with urinary sediment. The ESCOP monograph lists the therapeutic indications as irrigation of the urinary tract, especially in cases of inflammation and renal gravel, as an adjuvant in the treatment of bacterial infections of the urinary tract, and topically as a wound healing agent. E. arvense is regulated as a traditional phytomedicine and diuretic agent by the European Medicine Agency (EMA) and Brazilian National Health Surveillance Agency (ANVISA).

References

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• Carneiro DM et al. Antihypertensive effect of Equisetum arvense L.: a double-blind, randomized efficacy and safety clinical trial. Phytomedicine. 2022;99:153955.
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