Horsetail
Equisetum arvense
An ancient fern relative with the highest silica content of any medicinal plant, used traditionally as a diuretic and for hair, nail, and bone strength; clinical evidence is limited to small studies.
At a Glance
- Best known for
- Richest botanical source of bioavailable silica, Mild diuretic (confirmed in a small RCT), Traditional support for hair, nails, and connective tissue
- Evidence
- Preliminary
- Typical dose
- 900 mg dried extract daily (300 mg 3x daily)
- Type
- Herb
What is Horsetail?
Horsetail (Equisetum arvense) is a primitive, spore-bearing plant whose ancestors grew as tall as trees 300 million years ago. Its hollow, jointed stems are so rich in abrasive silica that they were once used to scour pots ('scouring rush'). Greek and Roman physicians used it to stop bleeding and heal wounds, and European herbalists prescribed it as a diuretic for kidney and bladder complaints. The sterile green summer stems are the medicinal part. Today it is sold mainly for hair, skin, and nail strength and for urinary support. Field horsetail should not be confused with marsh horsetail (Equisetum palustre), which is toxic.
Known Health Benefits
How It Works
Horsetail's silica is present partly as soluble orthosilicic acid, the form the body can absorb. Silicon is a cofactor in collagen synthesis and cross-linking and in the formation of glycosaminoglycans, and it stimulates osteoblast activity, which is the rationale for hair, nail, skin, and bone uses. The flavonoids and the high potassium and mineral load produce a mild diuretic effect by increasing urine volume without the strong electrolyte loss of loop diuretics. Quercetin and kaempferol glycosides add antioxidant and anti-inflammatory activity, and extracts show antimicrobial effects against common urinary pathogens in vitro. Crude horsetail contains thiaminase, an enzyme that destroys vitamin B1, which is why prolonged use of unprocessed herb is discouraged.
What Research Says
Human trials are few and small. A 2014 Brazilian randomized, double-blind crossover study in 36 healthy men found 900 mg of dried horsetail extract daily produced a diuretic effect equivalent to hydrochlorothiazide 25 mg over 4 days, without significant electrolyte disturbance. A 2016 Italian study reported improved nail quality after 6 months of a horsetail-based nail lacquer, but it was uncontrolled. A 1999 Italian trial found an osteoporosis formula containing horsetail improved bone density, but the multi-ingredient design makes the horsetail contribution unclear. Preclinical work supports anti-inflammatory and antioxidant actions and collagen synthesis, and silicon supplementation in other forms (choline-stabilized orthosilicic acid) has shown modest hair and nail benefits in small RCTs. There are no good trials of horsetail for hair loss or kidney stones, and claims for these uses rest on tradition.
Active Compounds
Silicic acid and silicates (5–8% of dried herb), flavonoids (quercetin, kaempferol, apigenin glycosides), caffeic acid esters, potassium, trace thiaminase (in crude herb)
Forms & Bioavailability
Only a fraction of horsetail's silica is soluble orthosilicic acid that can be absorbed; most is insoluble silicate that passes through the gut. Long decoction (simmering 20–30 minutes) extracts more soluble silica into tea. Processed extracts marketed for hair and nails often standardize silica content and heat-treat the herb to deactivate thiaminase. Absorbed silicon is excreted through the kidneys within hours, so divided daily dosing is reasonable.
Dosage Guidance
| Use Case | Dosage |
|---|---|
| Mild diuretic / urinary support | 900 mg dried extract daily (300 mg 3x daily) |
| Hair, skin and nails | 300–500 mg standardized extract daily |
| Bone support | 500 mg extract daily with calcium and vitamin D |
| Tea | 2–3 tsp dried herb simmered 15–20 min |
| Tincture | 2–4 mL 1:5 tincture 3x daily |
Always consult a healthcare provider for personalized dosing.
Natural Food Sources
- Not a significant food; young shoots are occasionally eaten in Japan (tsukushi) after careful preparation
- Dietary silicon is otherwise found in whole grains, beer, green beans, bananas, and mineral water
Potential Side Effects
Generally well tolerated short term; thiamine (vitamin B1) depletion with prolonged use of crude herb; increased urination; rare stomach upset; nicotine-like toxicity reported only in grazing animals
Who Should Avoid It
- Kidney disease or impaired kidney function (diuretic effect and silica load)
- Heart failure or edema from cardiac or renal disease (not a substitute for prescribed diuretics)
- Thiamine deficiency, alcohol dependence, or malnutrition (thiaminase content)
- Lithium therapy (altered excretion)
- Pregnancy and breastfeeding (lack of safety data; nicotine-like alkaloid traces)
Pregnancy & Lactation
Avoid. Horsetail has no established safety record in pregnancy or breastfeeding, acts as a diuretic, and contains trace nicotine-like alkaloids and thiaminase. Topical products are a lower-risk alternative for hair and nail concerns.
Known Drug Interactions
Additive with diuretics (dehydration, potassium loss); may increase lithium levels through altered clearance; may reduce effect of some drugs via diuresis; may lower blood sugar additively; thiaminase may worsen effects of alcohol on thiamine status
Evidence Classification
Based on in vitro studies, animal models, pilot trials, or traditional use documentation. Clinical evidence is limited.
Frequently Asked Questions
Does horsetail really strengthen hair and nails?
The reasoning is sound: silicon is needed for collagen and keratin structure, and small trials of other bioavailable silicon supplements have shown modest improvements in hair strength and nail brittleness. Direct trials of oral horsetail are lacking, however, so the benefit is plausible but unproven. Give it at least 3–6 months, since nails and hair grow slowly.
Why do I hear it can deplete vitamin B1?
Crude horsetail contains thiaminase, an enzyme that breaks down thiamine (vitamin B1). This has caused serious illness in grazing livestock. In humans, short courses of tea or capsules are unlikely to matter, but prolonged daily use of unprocessed herb could lower thiamine, especially in people who drink heavily or eat poorly. Heat-treated or thiaminase-free extracts avoid the issue, as does a B-complex supplement.
Can horsetail help with kidney stones or UTIs?
It has been used traditionally to flush the urinary tract and is part of some European 'irrigation therapy' protocols with high fluid intake. Its diuretic effect is documented, but there are no trials showing it prevents stones or treats infections. A urinary infection needs medical assessment; horsetail is at most a supportive measure.
Is wild horsetail safe to harvest?
Only if you can reliably identify Equisetum arvense. Marsh horsetail (E. palustre) contains higher levels of toxic alkaloids, and horsetails growing in contaminated soil accumulate heavy metals. For medicinal use, a reputable commercial product is safer.
References
- Randomized, double-blind clinical trial to assess the acute diuretic effect of Equisetum arvense (field horsetail) in healthy volunteers. Carneiro DM, Freire RC, Honório TC, et al.. Evid Based Complement Alternat Med (2014)View study
- Equisetum arvense (common horsetail) modulates the function of inflammatory immunocompetent cells. Gründemann C, Lengen K, Sauer B, et al.. BMC Complement Altern Med (2014)
- Silicon: a review of its potential role in the prevention and treatment of postmenopausal osteoporosis. Price CT, Koval KJ, Langford JR. Int J Endocrinol (2013)
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This entry is for educational purposes only. It is not medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement regimen, especially if you take medications or have health conditions.