What is Field horsetail?

Field horsetail is a fern-like plant whose dried green stems are brewed as tea or sold in capsules. In European folk use it was taken mainly to make you pass more urine, and to feed nails, hair and bone.

The plant has no flowers and no true leaves. Its stems are jointed, hollow and rough, because they are loaded with silica, the mineral in sand and glass. German names for it are Ackerschachtelhalm and Zinnkraut.

The short verdict on evidence: human testing is thin and of low quality. One small trial points to a mild water-loss effect. Nothing solid supports it for bone, hair or nails in people.

A long record of folk use is not proof that a plant works, and it is not proof that it is safe. Both still have to be shown. That point applies to everything on this page.

How does Field horsetail work?

The honest answer is that how it acts in the body is not settled.

Horsetail is rich in silicic acid, a soluble form of silicon. Supporters argue that this silicon feeds bone, nail and hair tissue. That chain of steps has not been shown to work in people.

Flavonoids and potassium salts in the herb may nudge the kidneys to pass more water. A small trial in healthy men did find more urine output. The effect looks like water loss, not a change in body salts.

In test tubes and in animals, extracts slow some bacteria and calm swelling. Whether any of that happens inside a person is unknown.

The plant also holds thiaminase, an enzyme that breaks down vitamin B1 (thiamine). Horses and cattle that graze on it can develop a B1 deficiency. Heat may destroy much of the enzyme, but the risk still shapes how long the herb is used.

What forms does Field horsetail come in?

Dried cut herb for tea is the most common form across Europe.

You may also see these forms.

Capsules or tablets of powdered herb.

Liquid tinctures made with alcohol.

Concentrated extracts, sometimes labelled with a silicon figure.

Creams, ointments and bath additives for skin and minor wounds.

Check the Latin name Equisetum arvense on the label. Products called "bamboo silica" come from a different plant. Wild-picked horsetail is risky, because a toxic relative looks much the same.

Where it comes from:

European folk healers used horsetail for hundreds of years, and writers from the Roman era mentioned Equisetum species. The rough stems were also used to scour pots and polish wood and pewter, which is where the name Zinnkraut comes from.

Healers gave it as a tea to make people pass water, and for swollen legs, bladder trouble and gravel in the urine. It was packed onto cuts and nosebleeds to slow bleeding. Baths and compresses were used for slow-healing sores.

In the 20th century German herbal monographs listed it for flushing the urinary tract and for mild swelling after a knock or injury. Those listings rested largely on tradition and long use, not on strong trials. They are not a recommendation to treat yourself.

What does Field horsetail help with?

• Passing more urine (mild fluid retention): This is the best-supported use, and the support is still weak. One small trial in healthy men found urine output rose over four days. Body salts did not shift much in that study. That is one short study in young, well people. It does not show that horsetail helps swollen legs caused by heart, liver or kidney disease. Swelling of that kind needs a doctor, not a herbal tea.
• Flushing the urinary tract: Folk use paired horsetail tea with lots of plain water to wash out the bladder. German monographs listed this use, based mostly on tradition. There is no good trial showing it clears or prevents a urine infection. Burning, fever or blood in your urine needs medical care and often antibiotics. Delaying that can let an infection reach the kidneys.
• Brittle nails and thinning hair: Tradition tied the plant's silica to strong nails and hair. This is now the main selling point for horsetail capsules. Human evidence is very thin. A few small, industry-linked studies of silicon products report better nail hardness, but they are weak and hard to apply to horsetail tea. Treat the claim as unproven.
• Bone strength and osteoporosis (thin, weak bones): Silicon does appear in bone, and diets higher in silicon have been linked to better bone density in population surveys. That is a link, not proof, and it is about food, not this herb. No trial shows that horsetail builds bone or prevents a fracture. If you have osteoporosis, use treatments your doctor has checked. Horsetail is not a stand-in for them.
• Minor wounds and slow-healing skin: Horsetail ointment was packed onto sores and cuts in folk practice. One small trial in women after childbirth found a horsetail ointment eased pain in a healing surgical cut. That study was small and done at one site. It has not been repeated well. Deep, dirty or spreading wounds need proper care, not a herbal cream.
• Minor bleeding, in folk use: Crushed stems were pressed onto nosebleeds and grazes to stop bleeding. This claim rests on tradition alone. No human trial backs it. Bleeding that will not stop, or that soaks through a dressing, is an emergency.

What are the side effects of Field horsetail?

• Passing urine more often
• Upset stomach or nausea
• Low potassium with heavy or long use
• Muscle weakness or cramps, which can signal low potassium
• Headache
• Skin rash or allergic reaction
• Low vitamin B1 (thiamine) with long use, which can cause confusion and nerve problems
• Dehydration if fluid intake is low

Good to know:

Most people who take horsetail for a short time have no trouble, or only mild stomach upset and extra trips to the toilet.

The serious problems come from heavy or long use. Dropping potassium and dropping vitamin B1 are both real risks. Both matter much more if you are older, drink heavily, or take water pills.

Poisoning from a mix-up with marsh horsetail is rare but dangerous. That is a reason never to pick it yourself.

How much Field horsetail should you take?

• Recommended daily: This page gives label-level figures only. They are not advice for you. European tea labels usually carry about 2 to 3 g of dried herb per cup. Older herbal monographs listed roughly 6 g of dried herb a day as a usual upper amount. Capsule and extract strengths vary widely, so the pack is the only guide. Flushing the urinary tract means drinking plenty of plain water alongside. That approach is not safe for anyone with heart failure or kidney failure. Ask a pharmacist or doctor before you start.
• Best time of day: Timing does not change whether it works. Many people avoid taking it late in the day. If it does make you pass more urine, it can wake you at night.
• With or without food: Either way is fine. Taking it with food may settle a queasy stomach. Tea is often drunk between meals. If you use it to flush the urinary tract, drink plenty of water with it.
• Time to effect: If a urine effect happens at all, it starts within hours of a dose. For nails, hair and bone, sellers talk about two to three months. No trial supports that timeline. It may do nothing for you. That is a real and common outcome with this herb.
• How long to take it: Short use is the pattern on most labels, often a few weeks at a time. Two things drive that limit. The herb carries an enzyme that breaks down vitamin B1 (thiamine). It can also lower your potassium if you take a lot. No safe long-term period has been worked out in people. If you feel you need it for months, that is a reason to see a doctor instead.