Horsetail is a living fossil, the sole descendent of primitive plants that served as dinosaur snacks 100 million years ago. Horsetail contains unusually high levels of the element silicon, making the herb so abrasive that it can be used for polishing. In addition, the plant can incorporate dissolved gold and other minerals into its structure.
Medicinally, horsetail has been used for treating urinary disorders, wounds, gonorrhea, nosebleeds, digestive disorders, gout, and many other conditions.1
Silicon plays a role in bone health,2 and for this reason, horsetail has been recommended to prevent or treat osteoporosis, and to strengthen brittle nails. The famous German herbalist Rudolf Weiss also suggests that horsetail can relieve symptoms of rheumatoid arthritis.3 However, there is no real scientific evidence for these proposed uses.
The standard dosage of horsetail is 1 g in capsule or tea form up to 3 times daily, as needed. Medicinal horsetail should not be confused with its highly toxic relative, the marsh horsetail (Equisetum palustre)
Noticeable side effects from standard dosages of horsetail tea are rare. However, horsetail contains an enzyme that damages vitamin B 1 (thiamin) and has caused severe illness and even death in livestock that consumed too much of it.4 In Canada, horsetail products are required to undergo heating or other forms of processing to inactivate this harmful constituent.
Also, perhaps because horsetail contains low levels of nicotine, children have been known to become seriously ill from using the branches as blow guns.5 This plant can also concentrate toxic metals present in its environment.
For all of the above reasons, horsetail is not recommended for young children, pregnant or nursing women, or those with severe kidney or liver disease.
Individuals taking the medication lithium should use herbal diuretics such as horsetail only under the supervision of a physician, as becoming dehydrated while taking this medication can be dangerous.6
Horsetail may also cause loss of potassium, which may be dangerous for people taking drugs in the digitalis family.7,8
1. Duke JA. CRC Handbook of Medicinal Herbs. Boca Raton, Fla: CRC Press; 1985:492.
2. Fessenden RJ, Fessenden JS. The biological properties of silicon compounds. Adv Drug Res. 1987;4:95–132.
3. Weiss RF. Herbal Medicine. Gothenburg, Sweden: AB Arcanum; 1998:238–239.
4. Fabre B. Thiaminase activity in Equisetum arvense and its extracts. Planta Med Phytother. 1993;26:190–197.
5. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs, and Cosmetics. 2nd ed. New York, NY: Wiley; 1996:307.
6. Pyevich D, Bogenschutz MP. Herbal diuretics and lithium toxicity [letter]. Am J Psychiatry. 2001;158:1329.
7. Brinker F. Herb Contraindications and Drug Interactions: With Appendices Addressing Specific Conditions and Medicines. 2nd ed. Sandy, Ore: Eclectic Medical Publications; 1998:85.
8. Perez Gutierrez RM, Laguna GY, Walkowski A. Diuretic activity of Mexican equisetum. J Ethnopharmacol. 1985;14:269–272.
Last reviewed December 2015 by EBSCO CAM Review Board Last Updated: 12/15/2015