Horsetail belongs to Equisetum, the only genus in the family Equisetaceae. It is a descendant of a large, primeval plant that thrived 400 million years ago during the Paleozoic geological period. The genus name, Equisetum, comes from two Latin words which mean "bristle horse." It bears this name because its stems are rich in silica and silicic acids. As the plant dries, silica crystals form on the walls of cells in the stems and branches. These crystals give the ground plant material a scratching effect. It is for this reason that horsetail historically has been used to polish metal, particularly pewter. Horsetail is also known as "scouring rush" and "pewterwort," appropriate synonyms in light of these traditional uses for the plant.

Studies on the flavonoid compounds in Equisetum arvense reveal that this species has two discrete chemotypes, or chemical subspecies. One chemotype is native to North America and the Far East, including China, Japan, and Siberia, while the other is indigenous to Europe. Horsetail is now widespread throughout parts of Europe, Asia, the Middle East, and North America.

Closely related to the ferns, horsetail is a non-flowering weed that flourishes on clay-filled, sandy soils. It is technically a pteridophyte and, as in the case of ferns, reproduces through spores. Pteridophytes are flowerless plants that have two distinct and alternating generations. The first is a non-sexual, spore-bearing generation of relatively larger plants. The second generation is sexual, and composed of smaller plants that lack well-differentiated stems and leaves. Equisetum species can also propagate non-sexually through stolons and tubers.

Best known as a mild diuretic, the aerial parts of horsetail are used medicinally for numerous ailments. The astringent properties of this plant render it a valuable treatment for kidney and bladder complaints, as well as an external therapy for bleeding wounds. Although horsetail is also indicated for dropsy, rheumatic conditions, and tuberculosis, there is no pharmacological evidence that it is effective in treating conditions other than mild water retention.

While horsetail remedies prepared from Equisetum arvense are basically safe, other Equisetum species such as Equisetum palustre contain poisonous alkaloidal constituents. Every effort should thus be made to ensure that horsetail herbal preparations are made from Equisetum arvense. The authenticity of Equisetum arvense should be confirmed by both morphological and chemical studies using microscopy and thin layer chromatography (TLC).

Horsetail is a perennial with the two distinct forms of stems. Between March and April, red-brown to straw-yellow fertile stems grow up to 20 cm in height. These pencil-slim stems bear brown, scale-like leaves arranged in whorls. At the tip of each stem is a scaly head containing a spore that is easily transported by the wind to other plants for sexual reproduction.

By early summer, usually during May and June, longer, sterile green stems appear that form a pale green brush up to 35 cm high. These barren stems give of multiple branches arranged in whorls at the nodes. The sterile stems and branches are characterized by deep grooves, a square-shape, and a rough texture. Both the fertile and barren stems are erect, jointed, and brittle. However, only the sterile stems are used medicinally.

Herb (fresh or dried sterile, green shoots).

Flavonoids (particularly quercetin 3-glucoside and its 6"-malonyl ester are found in both chemotypes; also kaempferol-, luteolin-, genkwanin-3-O-glucosides; 5-0-, 7-0-glucosides; and diglucosides); caffeic acid ester (chlorogenic acid, dicoffeoyl-meso-tartaric acid); silicic acid (partially water-soluble); styrolpyrone glucoside (equisetumpyron); pyridine alkaloids (nicotine in trace amounts). The purported presence of equisetonin, a saponin of unknown structure, requires confirmation.

Available as dried herb and liquid preparations made from the fresh or dried, green, sterile shoots of Equisetum arvense. Horsetail preparations should be stored in well-sealed containers to ensure protection from light.

Traditional uses: tuberculosis; nasal, pulmonary, and gastric hemorrhages; brittle fingernails and hair loss; rheumatic diseases; gout; catarrh for kidney and bladder areas; hematostatic (a therapeutic agent that stops bleeding) for profuse menstruation; stubborn wounds and ulcers, swelling and fracture; frostbite.

Conditions:

• Internal: inflammation or mild infections of the genito-urinary tract, kidney stones, bladder stones
• External: wounds, burns, poorly healing wounds, rheumatic conditions, fractures, sprains

Clinical applications: 

• Internal: post-traumatic and static edemal, flushing-out (irrigation) treatment for bacterial and inflammatory diseases of the lower urinary tract; kidney stones
• External: supportive therapy for poorly healing wounds

Although pharmacological investigations on Equisetum arvense are limited, this herb has been shown to have mild diuretic, hemostatic (arresting the blood flow), and vulnerary (wound-healing) properties. In addition, horsetail induces mild leucocytosis (a transient increase in white blood cell count).

In vivo studies confirm that horsetail has weak diuretic action, but research findings have been inconsistent. Flavonoids presumably account for the diuretic effect, which apparently does not involve an increase in electrolyte excretion. However, other evidence suggests that the diuretic activity of horsetail results from the combined pharmacological action of flavone glycosides and the saponin.

In other animal studies, horsetail was shown to produce a hemostatic effect. Therapeutic claims that horsetail and its active constituents, silica and silicic acid derivatives, promote tissue repair of bleeding pulmonary tubercular lesions have not been fully substantiated. However, in other research, the silicic acid content of horsetail reportedly had a strengthening and regenerative effect on connective tissues.

• Internal: 6 g per day
• Herbal infusion: 4 oz. tid
• Tincture (1:5): 1 to 4 ml tid
• External (compresses): 10 g of herb per 1 liter water per day

Adequate fluid should be taken when using oral horsetail preparations for irrigation therapy. A tea is prepared by pouring boiled water over 2 to 3 g horsetail herb, boiling for five minutes, and then straining after 10 to 15 minutes. Drink during the day between meals. An infusion for internal use is made by adding 1.5 g of horsetail herb to 1 cup of boiling water. Let steep 30 to 40 minutes.

Health risks and side effects have not been reported for horsetail when taken in recommended therapeutic doses. However, it is advisable to consult a health care practitioner when using fresh horsetail as a bath additive to treat major skin lesions, acute skin lesions of unknown origin, feverish and infectious diseases, or hypertonia (increased muscle resistance to passive stretching).

Horsetail is contraindicated in patients who have edema concomitant to cardiac or renal dysfunction. A related species, Equisetum palustre, is potentially toxic since it contains lapustrin, a poisonous alkaloid.

Although horsetail reportedly possesses diuretic properties, no clinically significant interactions between horsetail and conventional medications are known to have been reported in the literature to date, including the German Commission E monograph (Blumenthal 1998).

Horsetail herb is approved by the German Commission E. In the United Kingdom, horsetail is on the General Sale List, Schedule 2, Table A (R1a).

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