Stack Genius ingredient guide
Horsetail
A fern-like plant used as a supplement mostly for its silica content, marketed for hair, skin, nails, and bone support.
Overview
Horsetail — Equisetum arvense — is an ancient, non-flowering plant that looks a bit like a bottle brush and has been used medicinally in Europe for centuries. In supplements it is prized mostly for its silica content, which is the reason it turns up in "hair, skin, and nails" formulas alongside biotin, and in some bone-focused products.
Beyond silica, horsetail is used traditionally as a mild diuretic and as a source of minerals like potassium and manganese. Modern supplement marketing tends to lean hardest on the beauty-and-connective-tissue angle, though the human evidence base is thin.
The two safety details that actually matter: Equisetum arvense contains an enzyme called thiaminase that can break down vitamin B1, so any serious supplement should use a thiaminase-inactivated extract, and the closely related Equisetum palustre is toxic and should never be substituted.
Key takeaways
- Traditional silica source used in hair, skin, nail, and bone support formulas.
- Use thiaminase-free extracts of Equisetum arvense; avoid marsh horsetail (Equisetum palustre) entirely.
- Mild diuretic effects can matter for people on diuretics, lithium, or with kidney disease.
Practical guidance
What to know before adding Horsetail
Evidence snapshot
Human evidence for horsetail is limited. A small trial suggested a horsetail-based silica preparation improved bone density in postmenopausal women, and there is some evidence for mild diuretic effects. Data supporting hair growth, nail strength, or skin improvements is largely anecdotal or based on the general role of silica in connective tissue rather than horsetail-specific studies.
What to look for on the label
Look for a product that specifies Equisetum arvense (never palustre), states that the extract is thiaminase-free or thiaminase-inactivated, and quantifies silica or silicon content per serving. Standardized extracts and identified extract ratios are more meaningful than raw powder listed only by milligram weight.
What makes a better product
For horsetail, the key quality clues are Equisetum arvense, aerial parts, disclosed silica or silicon content, and evidence that the thiaminase issue is controlled. Unknown bulk powders are harder to trust because species identity and processing matter here.
Watch-outs
Because horsetail acts as a mild diuretic, it can increase fluid and electrolyte losses and should be avoided or used cautiously with prescription diuretics and lithium. Long-term use of non-thiaminase-inactivated products has been linked to thiamine deficiency. People with heart failure, kidney disease, gout, or on medications where electrolyte shifts matter should check with a clinician. Marsh horsetail (E. palustre) is toxic and must never be used.
Dosing & Timing
Standardized extracts vary widely, and no single consensus dose exists. Trials and traditional use suggest 300 to 900 mg of extract per day, divided across meals. Given the diuretic effect, taking it earlier in the day and staying well hydrated is sensible. Given thiamine-related concerns, cycling off or using it intermittently rather than continuously long-term is a reasonable precaution.
Safety and interaction context
Non-thiaminase-inactivated horsetail can deplete vitamin B1 with sustained use, which is particularly risky for people with alcohol use disorders or malnutrition. Diuretic effects may compound the action of loop or thiazide diuretics and can raise lithium levels. Nicotine content in horsetail is small but real, which matters more for children than adults. Not recommended during pregnancy and breastfeeding due to limited safety data.
Sources
- MedlinePlus — HorsetailThiaminase content and safety notes.
- NCCIH - Using Dietary Supplements WiselyFederal guidance on supplement safety, quality, and clinician review.
Track products by ingredient in Stack Genius
Use Stack Genius to connect supplement products back to ingredients, spot overlap, and keep your routine organized.