Horsetail tea is most commonly used as a natural diuretic, but it also has a reputation for supporting bone strength, hair growth, and reducing inflammation. Made from the dried stems of a plant that has existed since the age of dinosaurs, horsetail stands out because of its unusually high silica content, which can reach up to 25% of the plant’s dry weight. That mineral concentration is what drives most of the tea’s proposed benefits.
A Natural Diuretic on Par With Medication
The best-studied benefit of horsetail tea is its ability to increase urine output. In a randomized, double-blind clinical trial with healthy volunteers, horsetail extract produced a diuretic effect equivalent to hydrochlorothiazide, a commonly prescribed water pill. Participants who took the horsetail extract had a significant net fluid loss of about 322 mL compared to placebo, with no meaningful difference from the prescription drug group.
What makes this particularly interesting is that horsetail didn’t significantly alter the body’s excretion of sodium or potassium, which are electrolytes that prescription diuretics often deplete. Germany’s Commission E, a regulatory body for herbal medicines, has approved horsetail for treating post-injury and chronic swelling (edema) and as a diuretic for inflammatory conditions of the urinary tract. The plant’s high concentration of flavonoids, phenolic compounds, and potassium salts appears to drive this effect, though the exact mechanism isn’t fully understood.
Bone Health and Calcium Absorption
Silica plays a quiet but important role in how your body builds and maintains bone. It helps with calcium absorption and supports collagen production, the protein scaffolding that gives bones their flexibility and resilience. Horsetail has been shown to enhance the proliferation of osteoblasts (cells that build new bone) while inhibiting osteoclasts (cells that break bone down).
In an animal study modeling postmenopausal osteoporosis, adding horsetail extract to a bone-supporting nutrient mix produced measurable improvements. Cortical bone thickness and trabecular width both increased significantly compared to untreated subjects. The combination of horsetail with bone-mineralizing nutrients was actually more effective at preventing osteoporotic bone loss than raloxifene, a standard osteoporosis drug used as the comparison. Enzyme markers in the treated group returned to normal levels, indicating that the herb helped accelerate mineralization of the bone’s organic framework. These are animal results, not human trials, but they align with horsetail’s long traditional use for bone conditions.
Hair Growth and Stronger Nails
Silica’s role in collagen production extends to hair and nails. In a three-month study, women who perceived their hair as thinning took two daily capsules containing dried horsetail (along with other ingredients) and experienced increased hair growth and strength compared to a control group. Several other studies using silica derived from horsetail have shown similar results.
For nails, horsetail extract has been incorporated into nail lacquers to address brittleness and even nail psoriasis, a condition that causes nail deformities. A study using a nail polish blended with horsetail extract and other hardening agents found it reduced visible signs of nail psoriasis. The common thread is silica’s contribution to the structural proteins that keep hair and nails strong.
Anti-Inflammatory Effects
Lab research shows that horsetail extract dials down several key players in the inflammatory response. It reduced the production of TNF-alpha and IFN-gamma, two signaling molecules that drive inflammation, in activated immune cells. It also suppressed the early activation of those cells in a dose-dependent manner, meaning higher concentrations produced a stronger calming effect. At its most concentrated dose, horsetail cut the production of a key immune-signaling protein roughly in half compared to untreated cells.
This anti-inflammatory activity, combined with the plant’s documented antioxidant and antibacterial properties, likely explains why horsetail tea has been used traditionally for urinary tract discomfort and general swelling. The effects observed in the lab are promising, though more human studies are needed to confirm how well these results translate from a petri dish to a cup of tea.
How to Brew Horsetail Tea
Add one tablespoon (about 2 to 3 grams) of dried horsetail stems to one cup of boiling water. Cover and let it steep for 5 to 10 minutes, then strain. Covering the cup while steeping helps trap volatile compounds and heat, which improves mineral extraction. Most traditional preparations suggest drinking one to three cups per day, though it’s best not to use horsetail tea continuously for extended periods.
Safety Concerns and Who Should Avoid It
Horsetail contains an enzyme called thiaminase, which breaks down thiamine (vitamin B1) and renders it inactive. In animals, consuming significant amounts of horsetail for two to five weeks produces signs of thiamine deficiency. For humans, this means prolonged daily use without breaks could deplete your B1 levels, especially if your thiamine stores are already low. People with alcohol use disorder are at particular risk, since they tend to already be thiamine deficient.
Several medication interactions are worth knowing about:
- Lithium: Horsetail may slow the body’s elimination of lithium, allowing it to build up to potentially dangerous levels.
- Diabetes medications: Because horsetail can lower blood sugar, combining it with diabetes drugs could cause blood sugar to drop too low.
- Prescription diuretics: Stacking horsetail’s natural diuretic effect with water pills could cause potassium levels to fall dangerously low.
- HIV medications: Horsetail may reduce the effectiveness of certain antiretroviral drugs, including NRTIs and efavirenz.
Horsetail also contains trace amounts of nicotine, so people with nicotine allergies may react to it. Those with carrot allergies sometimes cross-react to horsetail as well. There isn’t enough safety data to support use during pregnancy or breastfeeding. If you have low potassium levels or existing thiamine deficiency, horsetail tea could worsen both conditions.