Horsetail tea has mild diuretic properties and may support kidney health in people with normal kidney function, but it poses real risks for anyone with existing kidney disease. The evidence is promising in a few specific areas, particularly urinary tract protection and kidney stone prevention, though much of it comes from small studies or animal research.
How Horsetail Affects the Kidneys
Horsetail works on the kidneys in two main ways. First, it increases urine output, flushing more fluid through your urinary tract. A clinical trial comparing horsetail extract (900 mg per day) to the prescription diuretic hydrochlorothiazide (25 mg per day) found no significant difference between the two in lowering blood pressure over three months. The horsetail extract reduced systolic blood pressure by about 12.6 mmHg and diastolic by 8.1 mmHg, comparable results to the pharmaceutical drug, with virtually no adverse effects reported.
Second, and perhaps more interesting, horsetail appears to stimulate production of a protective protein in the kidneys called uromodulin. In a seven-day study, people taking horsetail extract saw uromodulin levels in their urine jump by up to 300% compared to untreated controls. This protein plays a role in preventing kidney gravel from forming and defending against urinary tract infections caused by E. coli. That dual action, more urine flow plus more of this protective protein, is what makes horsetail stand out from simple diuretics.
Kidney Stones and Urinary Gravel
The potential to prevent kidney stones is one of the more compelling reasons people reach for horsetail tea. Animal studies have tested a plant mixture containing horsetail alongside three other herbs and found it prevented calcium oxalate crystal deposits and microcalcifications in the kidneys. It’s worth noting that these results come from a combination product, not horsetail alone, so it’s difficult to isolate exactly how much horsetail contributed. Still, the increased uromodulin production observed with horsetail on its own provides a plausible mechanism for stone prevention, since this protein helps keep minerals from clumping together in the urinary tract.
The diuretic effect also helps by diluting urine and moving minerals through the system faster, giving crystals less time to form. If you’re prone to kidney stones, staying well-hydrated is the single most effective prevention strategy, and horsetail tea at least contributes to that fluid intake while potentially adding extra protective benefits.
Silica: The Signature Mineral
Horsetail contains more silica than any other plant. Up to 25% of its dry weight is silica, a mineral involved in connective tissue health. Some people drink horsetail tea specifically for silica’s benefits to hair, skin, and nails, but it’s worth knowing that silica excretion in urine showed no correlation with the kidney-protective uromodulin levels in clinical testing. In other words, silica doesn’t appear to be the ingredient responsible for horsetail’s kidney benefits. The diuretic and uromodulin-stimulating effects likely come from other compounds in the plant, including its flavonoids.
Who Should Avoid Horsetail Tea
If you have kidney disease, horsetail tea is not safe. The European Medicines Agency states that horsetail medicines must not be used for urinary complaints when reduced fluid intake is recommended due to severe heart or kidney disease. In people with compromised kidneys, horsetail can raise potassium levels to dangerous territory because the kidneys can’t clear the excess efficiently. This applies to chronic kidney disease at any stage where your doctor has flagged potassium as a concern.
There are a few other safety issues to keep in mind. Horsetail contains an enzyme called thiaminase, which breaks down vitamin B1 (thiamine) in the body. This is well documented in veterinary medicine, where horses grazing on horsetail develop thiamine deficiency. For humans drinking occasional cups of tea, this is unlikely to cause problems, but long-term daily use could theoretically deplete B1 stores, especially if your diet is already low in this vitamin.
Species identification also matters. The horsetail used in herbal medicine is Equisetum arvense, sometimes called field horsetail. A different species, Equisetum palustre (marsh horsetail), is toxic and explicitly contraindicated for human use. If you’re buying loose dried horsetail rather than a standardized product, misidentification is a real concern.
Contamination Risks
Horsetail is an aggressive bioaccumulator of heavy metals, particularly zinc. U.S. Geological Survey research found that horsetail consistently absorbs more zinc from soil than other plants growing in the same area. On contaminated ground, the plant accumulated up to 9,000 parts per million of zinc in its ash. Lead absorption followed a similar pattern: background levels were low at 13 ppm, but plants growing near old mining sites reached 350 to 420 ppm.
This matters because you’re essentially drinking whatever the plant pulled from the soil. Horsetail tea from a reputable brand that tests for heavy metals is a very different product from wild-harvested horsetail of unknown origin. If you’re buying horsetail tea, look for products that specify testing for contaminants.
Dosage and Duration
Clinical trials have used standardized dry horsetail extract at 900 mg per day (split into three doses), which is considered the maximum recommended dose for dry extracts. Studies have run from four days to three months at this dose without significant adverse effects in healthy adults. Brewed tea is harder to standardize because the concentration depends on steeping time, water temperature, and the quality of the dried herb, but one to three cups per day is the range most herbalists suggest.
There is no established consensus on how long you can safely take horsetail continuously. The thiaminase concern and the lack of long-term safety data both argue for cycling it rather than making it a permanent daily habit. Some practitioners recommend limiting continuous use to a few weeks at a time, though firm clinical guidance on this point doesn’t exist.
The Bottom Line on Kidney Health
For people with healthy kidneys, horsetail tea is a reasonable herbal option that increases urine output, may help prevent kidney stones, and boosts a protective protein in the urinary tract. Its diuretic strength is comparable to a common prescription water pill, at least over a few months. But it is not a treatment for kidney disease, and it can actively worsen things if your kidneys are already struggling. The quality of the product you buy matters more than with most herbal teas, given horsetail’s tendency to soak up heavy metals from contaminated soil.