Horsetail Tea: What to Know Before You Brew

Field horsetail (Equisetum arvense) is a plant with hollow, jointed green stems that look a little like tiny bamboo. It grows in damp ground across Europe, Asia and North America, and the dried green stems have long been brewed into a mild, grassy tea.

In European tradition, horsetail is used to increase the amount of urine you pass. That single effect explains both why people reach for it and why it needs care. This guide covers how it is traditionally made, what the evidence actually says, and the people who should leave it alone.

Why people use it

The European Medicines Agency (EMA) lists horsetail as a traditional herbal medicine for two uses: to increase urine output and help flush the urinary tract in minor urinary complaints, and, applied on the skin, as a support for small, superficial wounds.

Traditional means the use is accepted because it has been around safely for a long time, not because clinical trials have proven that it works. The EMA states this clearly.

What the evidence says

Human research is thin. The EMA assessment describes one small, double-blind trial in 36 healthy young men. A dried horsetail extract taken for four days made them pass more fluid than a placebo, roughly similar to a low dose of a common prescription water pill, without changing their salt or potassium levels.

The EMA reviewers judged that this was not enough to prove a well-established medical use. The trial was small, tested an extract rather than home-brewed tea, and involved healthy people, not people with any illness.

So the honest summary is this: horsetail may act as a mild diuretic, and its traditional use for minor urinary complaints is accepted in the EU. There is no good evidence that it helps with any disease, and it is not a way to lose weight or remove so-called toxins.

Thiamine, look-alikes and other specific risks

Horsetail contains an enzyme called thiaminase, which breaks down thiamine (vitamin B1). The EMA assessment reports that horses poisoned by eating horsetail recovered with thiamine injections. The same report notes that heat inactivates the enzyme, and it was not found in water-based extracts. That is one reason to use the herb only as a properly brewed hot tea and not as raw, unheated powder, where the reviewers could not rule out harm.

A related plant, marsh horsetail (Equisetum palustre), is toxic. The EMA notes that dried horsetail can be mixed up with it when it is gathered by people who cannot tell the species apart. Do not pick your own unless you are an expert, and buy dried herb only from a seller that tests and identifies it.

The EMA also mentions that small amounts of nicotine may be present, and that people sensitive to nicotine may react. Allergic reactions, including rash and facial swelling, and mild stomach upset have been reported.

Questions people ask

This article is for general information only and is not medical advice. Herbs can interact with medicines and health conditions. Talk to a doctor or pharmacist before trying a herbal remedy, especially if you are pregnant, breastfeeding, giving it to a child, or taking any medication.