Cola de caballo, known in English as horsetail (Equisetum arvense), is an herbal remedy used for centuries as a natural diuretic, a bone-strengthening supplement, and a way to improve hair, skin, and nail health. The plant stands out because it contains up to 25% silica by dry weight, a mineral that plays a direct role in collagen production and connective tissue maintenance. Most people encounter it as a dried tea or capsule supplement, and a growing number of clinical trials support several of its traditional uses.
A Natural Diuretic Without Electrolyte Loss
The most popular traditional use of cola de caballo is as a diuretic, helping the body flush excess water. A randomized, double-blind clinical trial in healthy volunteers found that horsetail extract produced a diuretic effect equivalent to hydrochlorothiazide, one of the most commonly prescribed water pills. The key difference: horsetail did not cause significant changes in electrolyte elimination. Standard diuretics often deplete potassium and sodium, which can lead to muscle cramps, fatigue, and heart rhythm issues. Horsetail appears to sidestep that problem, at least in the short term.
This makes cola de caballo tea a common choice for mild water retention, bloating, and urinary tract support in Latin American and European herbal traditions. It’s typically brewed by steeping the dried stems in hot water for 5 to 10 minutes and drinking one to three cups per day.
Bone Health and Mineral Density
Silica is essential for the body’s ability to use calcium and build bone tissue, and horsetail is one of the richest plant sources available. A randomized, double-blind study in postmenopausal women with osteoporosis tested a titrated horsetail extract combined with calcium over one year. Bone densitometry scans showed a clear increase in vertebral bone density, with an average recovery of bone mass around 2.3%. The treatment also improved scores on the Nordin test, a clinical measure of bone metabolism.
A 2.3% gain may sound small, but for postmenopausal women actively losing bone, reversing that trend is significant. Prescription osteoporosis drugs typically aim for gains in a similar range. The silica in cola de caballo helps the body deposit calcium where it belongs, essentially acting as a building scaffold for new bone tissue.
Hair Thickness and Nail Strength
The same silica content that supports bones also benefits hair and nails. Two well-designed trials looked at a bioavailable form of silica derived from horsetail (choline-stabilized orthosilicic acid at 10 mg per day) and found measurable improvements in both.
In a 20-week randomized, placebo-controlled study of women with photoaged skin, those taking the supplement had significantly lower scores for hair and nail brittleness compared to the placebo group. A separate 9-month trial in women with fine hair measured actual changes in hair structure: the supplement group showed a significant increase in cross-sectional area, meaning their individual hair strands became physically thicker.
These aren’t dramatic overnight changes. The 9-month timeline reflects the slow pace of hair growth, but the results were consistent and statistically significant. If you’re dealing with thinning hair or nails that split and peel easily, cola de caballo is one of the better-studied herbal options.
Wound Healing and Skin Repair
Horsetail has a long history as a topical wound treatment, and recent research helps explain why it works. In animal studies, topical application of horsetail extract accelerated wound healing in diabetic subjects by promoting fibroblast migration into damaged tissue and increasing collagen synthesis. Fibroblasts are the cells responsible for rebuilding skin after an injury, and collagen is the structural protein that gives healed skin its strength.
The extract contains several active compounds that work together on different phases of healing. Some reduce the overactive inflammatory response that slows repair, while others directly stimulate new collagen production. In diabetic subjects (whose wounds are notoriously slow to heal), treated skin showed a collagen layer comparable to that of non-diabetic controls. The most effective concentration produced a notably compact, well-organized collagen structure in the healed area.
Safety and Limitations
Cola de caballo is generally well tolerated as a tea or standardized supplement when used for reasonable periods. The primary safety concern involves an enzyme called thiaminase, which breaks down vitamin B1 (thiamine) in the body. In animals, consuming large amounts of horsetail (20% or more of their diet) leads to symptoms of thiamine deficiency within two to five weeks. For humans drinking a few cups of tea per day, this is unlikely to be an issue, but extended daily use over many weeks could theoretically lower B1 levels.
Cooking and processing may not fully destroy thiaminase, so it’s worth being cautious about very long-term, high-dose use. Taking a B-complex vitamin alongside cola de caballo is a simple precaution if you plan to use it regularly. People already taking prescription diuretics or medications for blood pressure, kidney disease, or diabetes should be careful about stacking horsetail’s diuretic effect on top of their existing treatment.
How People Typically Use It
The most common forms are dried herb for tea, capsules containing powdered or extracted horsetail, and liquid tinctures. Tea is the traditional preparation throughout Latin America and remains the most accessible option. For hair and nail benefits specifically, the clinical evidence used 10 mg of bioavailable silica daily, taken as a capsule for at least five months to see results.
For diuretic and general wellness purposes, one to three cups of brewed tea per day is the standard range in traditional use. Capsule supplements vary widely in concentration and standardization, so looking for products that specify silica content gives you a better sense of what you’re actually getting. Since the plant’s benefits are closely tied to its mineral content, higher-silica preparations tend to be more effective than generic dried-herb capsules.