Herb library · Herb · Equisetum arvense
Horsetail
A jointed, silica-rich relative of the ferns, taken as a tea to increase urine flow and used on minor skin wounds. One small trial in healthy men found a mild water-pill effect; the rest of its use rests on tradition.
Traditional use
Horsetail's stems are so rich in silica that they were once used to scour and polish. In Europe the dried stems are taken as a tea or extract to increase urine and flush the urinary tract in minor urinary complaints, and a decoction or the pressed juice is used on the skin for superficial wounds. The European Medicines Agency accepts both uses on the basis of long-standing use alone.
What studies show
- Limited
Urine flow: one double-blind trial in 36 healthy men found a dry extract increased urine output about as much as the water pill hydrochlorothiazide, without changing sodium or potassium loss. The EMA judged the study too small, and its extract too poorly described, to establish the effect.
- Insufficient
Minor urinary complaints and superficial wounds: no clinical trials; the EMA's acceptance rests on long-standing use.
Be careful of
Cautions
- ConditionDo not use it to increase urine if you have been told to limit fluids, for example with severe heart or kidney disease. People whose kidneys handle potassium poorly were advised to be cautious, because horsetail contains a lot of potassium.
- ConditionSee a doctor if you have fever, painful urination, cramps or blood in the urine, if symptoms last longer than a week, or if a wound shows signs of infection.
- NoteMild stomach complaints and allergic reactions such as rash and facial swelling have been reported. People sensitive to nicotine may react, since the plant may contain traces of it.
- NoteBuy quality-controlled products: horsetail can be mixed up with marsh horsetail (Equisetum palustre), which contains a toxic alkaloid. The raw plant contains an enzyme that destroys thiamine (vitamin B1); heating and alcohol extraction inactivate it, and Canada requires horsetail products to be free of it.
- NoteLiverTox reports that oral horsetail has been linked to rises in liver enzymes but not convincingly to liver injury with jaundice. The EMA describes one case of severe hepatitis in a man with hepatitis B who drank about eight times the traditional daily amount of juice.
- PregnancySafety in pregnancy and breastfeeding has not been established, and the EMA does not recommend it then. Do not apply it to the breast while breastfeeding. Not recommended for children under 12.
- Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.
From the old books
What herbals and dispensaries of the past printed. History, in their words.
“Silica enters largely into the composition of these plants, on which account they have been used to scour, rough polish, etc.”
Sources
- European Union herbal monograph on Equisetum arvense L., herba (opens in a new tab) · EMA · read September 25, 2026
- Assessment report on Equisetum arvense L., herba (opens in a new tab) · EMA · read September 25, 2026
- Horsetail (LiverTox) (opens in a new tab) · NIH · read September 25, 2026
Reviewed September 25, 2026.