Know2eat

Horsetail

Equisetum arvense

Herbs & Botanicals

What horsetail may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedBone mineral densityNot enough evidence· 2 sources

Then, in order

About Horsetail

The sterile stems of a primitive spore-bearing plant, notable for a high silica content. Sold for hair, nails and as a traditional diuretic.

Horsetail is marketed almost entirely on its silica content, with human evidence that is thin to absent for hair and nails. Two safety issues matter more than the claims: some Equisetum species contain thiaminase, which degrades vitamin B1 and has caused deficiency in grazing animals, and the closely related Equisetum palustre contains toxic alkaloids and is a documented adulterant.

Sold as
Dried herb capsule, Extract, Tea, Tincture, Silica supplements
Standardised to
Occasionally standardised to silica content — a product without this marker may not resemble what was studied.
Also known as
Equisetum, Shavegrass, Bottlebrush

What the research used

The amounts, forms and durations published trials of Horsetail actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Diuretic effect

    900 mg

    Not enough

    Dried extract, divided doses · 4 days

    From one small Brazilian crossover study comparing it against hydrochlorothiazide over a few days. That is the extent of the controlled human dosing data.

  • Studied for Hair and nail use

    300–1000 mg

    Not enough

    Dried herb or extract capsule

    Retail dosing with no supporting trials. Where hair studies exist, horsetail was one ingredient in a multi-nutrient product.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.

  • Any time

    Not enough

    No timing has been examined in human studies.

    Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.

The evidence in depth

Best supported: Not enough

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Bone mineral density

Bone Health
Not enough evidence

There is no dependable human research linking horsetail silica to bone density, despite frequent marketing on that basis.

Not enough evidence. Not enough human research to say anything useful yet.

View the 2 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Hair growth and strength

Hair Health
Not enough evidence

There is not enough human research to say horsetail affects hair or nail growth. Trials that report improvements used multi-ingredient formulas in which horsetail was one of several components.

Not enough evidence. Not enough human research to say anything useful yet.

View the 2 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Kidney and urinary function

Kidney & Urinary Health
Not enough evidence

Evidence is limited for horsetail as a diuretic. One small short crossover study exists, which is not enough to draw a conclusion from.

Not enough evidence. Not enough human research to say anything useful yet.

View the 1 source

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Worth knowing

    Thiaminase and vitamin B1 depletion

    Horsetail contains thiaminase, which breaks down vitamin B1. Thiamine deficiency has been documented in livestock eating it, and prolonged human use is a theoretical risk, particularly alongside heavy alcohol use where thiamine status is already compromised.

  • Worth knowing

    Adulteration with toxic Equisetum palustre

    Marsh horsetail contains toxic piperidine alkaloids and is a recognised contaminant of harvested Equisetum arvense. Species verification is not something a consumer can do by eye.

  • Interaction

    Diuretics, lithium and potassium loss

    Interacts withDiuretics, lithium, digoxin

    A diuretic effect may add to prescribed diuretics, deplete potassium and alter lithium levels.

  • Avoid

    Pregnancy, breastfeeding and children

    Nicotine has been detected in some horsetail preparations, and safety data are absent. It is not appropriate in pregnancy, breastfeeding or childhood.

  • Worth knowing

    Kidney disease

    Anyone with kidney impairment should avoid diuretic herbs, whose effects on fluid and electrolyte balance are unmeasured and unmonitored.

Evidence ratings on this page: 3 not enough evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take Horsetail, or a dose to follow.