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Equisetum Arvense
A silica-rich traditional herb marketed for hair, nails, bone, and as a diuretic. Human evidence is thin: one good diuretic RCT and a topical wound-healing trial exist, but the hair/nail/bone claims rest mostly on tradition and in-vitro data. It also contains thiaminase, which can deplete vitamin B1.
What the evidence says
Most Horsetail studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from medium-quality randomised trials published 2011–2015 with a typical study size of 36 participants.
Based on 4 studies · 2 RCTs · 145 total participants
Confidence
Low confidenceBy outcome
Scored low/Emerging because the only solid human data are a single diuretic crossover RCT and a topical wound trial; the headline hair/nail/bone claims rest on in-vitro and traditional use, plus a thiaminase safety concern.
1 trial ongoing or recruiting · 6 completed on ClinicalTrials.gov
1 of the completed trials have posted results
Registered trials show research momentum for Horsetail, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Sep 2026
Horsetail (Equisetum arvense) is an ancient plant valued for its high silica content and used traditionally as a diuretic and for hair, nails, skin, and bone. The marketing leans heavily on silicon being a structural mineral for connective tissue, but the actual human evidence is limited and indirect.
The strongest data are off-target: a well-conducted Brazilian RCT found a standardized horsetail extract had a genuine diuretic effect comparable to hydrochlorothiazide, and a topical-ointment trial showed faster episiotomy wound healing.
For the headline hair/nail/bone claims there are essentially no robust oral human efficacy trials — only in-vitro work (e.g., inhibition of osteoclast formation) and traditional use.
A real safety caveat: horsetail contains thiaminase, an enzyme that breaks down thiamine (vitamin B1); chronic use has been linked in a case report to thiamine deficiency, so prolonged or high-dose use is discouraged.
Horsetail is rich in silica; silicon is a structural component of connective tissue, the basis for hair/nail/bone marketing — but oral cosmetic efficacy is unproven.
A standardized extract produced a measurable diuretic effect in a controlled trial, without significant electrolyte loss.
A hydromethanolic extract inhibited human osteoclast formation in cell culture, a theoretical bone-protective mechanism.
How Horsetail works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Avoid — thiaminase content and a case report linking prenatal use to thiamine deficiency.
Avoid — additive risk of thiamine deficiency.
Use only with medical supervision.
Horsetail has its own diuretic activity; combining with prescription diuretics could increase fluid loss. Monitor.
Diuretic herbs can alter lithium clearance and raise levels. Avoid combining without monitoring.
Thiaminase content can degrade vitamin B1; chronic use may deplete thiamine, especially with poor diet or alcohol.
Tip: Expected diuretic effect; maintain hydration
Tip: Limit duration; supplement thiamine; avoid with alcohol
Horsetail has an evidence score of 3/10 — emerging evidence based on 4 indexed studies. A silica-rich traditional herb marketed for hair, nails, bone, and as a diuretic. Human evidence is thin: one good diuretic RCT and a topical wound-healing trial exist, but the hair/nail/bone claims rest mostly on tradition and in-vitro data. It also contains thiaminase, which can deplete vitamin B1. Representative study: PMID 26019907.
The commonly studied dose of Horsetail is Standardized dried extract ~900 mg/day (the diuretic-trial dose); no validated dose exists for hair/nail/bone use. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Horsetail is with meals. Take it with food. Taken with food; avoid prolonged use because of thiaminase content.
Horsetail should be used with caution — talk to a healthcare provider before taking it. The most commonly reported side effects are increased urination, thiamine (B1) depletion with chronic use. Use caution if any of these apply to you: Pregnancy/breastfeeding (thiaminase; a case report links prenatal use to thiamine deficiency); Thiamine (B1) deficiency or alcohol-use disorder; Use with potent diuretics (additive fluid/electrolyte effects).
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 4 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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