Cola de caballo, known in English as horsetail (Equisetum arvense), is an herbal remedy used primarily as a natural diuretic, an anti-inflammatory, and a source of silica for bone and skin health. It has a long history in European and Latin American traditional medicine, and modern research supports several of its uses. Here’s what the evidence actually shows.
A Natural Diuretic Comparable to Medication
The most well-studied use of cola de caballo is as a diuretic, meaning it helps your body flush out excess water. In a randomized, double-blind clinical trial, healthy volunteers took 900 mg per day of a standardized horsetail extract for four consecutive days. The horsetail group lost significantly more fluid than the placebo group, and the effect was statistically comparable to 25 mg of hydrochlorothiazide, a common pharmaceutical diuretic.
What makes this particularly interesting is that horsetail did not significantly alter sodium or potassium excretion in the study. Many prescription diuretics cause potassium loss, which can lead to muscle cramps and other problems. Researchers believe the diuretic action comes from the plant’s high concentration of flavonoids, phenolic compounds, and mineral salts, though the exact mechanism isn’t fully understood yet.
This is why cola de caballo tea is so widely used across Latin America for water retention, mild bloating, and urinary tract support.
Bone Health and Osteoporosis
Cola de caballo contains more than 10% inorganic substances, about two-thirds of which are silicic acid and potassium salts. That silica content is the key to its reputation for supporting bones. Silica helps your body deposit calcium and other minerals into bone tissue, stimulates the cells responsible for building new bone (osteoblasts), and supports the production of collagen and connective tissue.
In an animal study, rats given 120 mg/kg of horsetail extract showed significantly higher bone mineral density compared to a control group. The extract also contains ursolic acid and oleanolic acid, two compounds shown to promote bone-building cell activity while inhibiting the cells that break bone down. A separate study in postmenopausal women with osteoporosis found that horsetail extract combined with calcium supplements improved bone metabolism. Other research using a formulation of horsetail with soy isoflavones, lactoferrin, and vitamin D showed benefits for bone remodeling and reduced inflammatory markers.
None of this means cola de caballo replaces osteoporosis treatment, but the evidence for its bone-supporting role is more than just folklore.
Wound Healing and Skin Repair
Applied topically, cola de caballo speeds up wound healing. In a randomized placebo-controlled trial, a 3% horsetail ointment was applied to surgical wounds after childbirth. After 10 days, the group using the ointment saw an 86% improvement in wound healing scores, compared to just 15% in the placebo group. The ointment also reduced pain during recovery.
Animal studies back this up. In rabbits, horsetail ointment reduced wound size more effectively than zinc oxide ointment, and the overall healing in weeks two and three was notably better. Research in rats found that horsetail promoted reconstruction of both skin layers, increased blood vessel formation, and thickened the granulation tissue that forms during healing. The silicic acid, silicon, and natural compounds called saponins in the plant are thought to drive these effects.
Anti-Inflammatory Properties
In Europe, horsetail extracts have a long tradition in treating inflammatory conditions, and laboratory research has begun to explain why. Studies show that horsetail extract interferes with how immune cells function during inflammation, essentially dialing down the overactive immune response. This provides a plausible explanation for its traditional use in conditions like arthritis and inflammatory skin problems. Several of the plant’s known chemical components, including various flavonoids and phenolic acids, have individually demonstrated anti-inflammatory activity.
Hair and Nail Strength
Cola de caballo is widely marketed for hair growth and nail strength, largely because of its silicon content. Silicon plays a role in collagen production, which is a building block of hair and nails. A 2016 study found that daily silicon supplementation over nine months improved hair’s resistance to breaking, and a 2015 study showed that oral tablets containing horsetail-derived silica improved both hair strength and growth.
That said, a 2019 research review concluded there isn’t enough evidence to recommend horsetail as an effective treatment for hair loss specifically. The existing results are promising for hair quality and breakage, but if you’re dealing with significant hair loss, the evidence isn’t strong enough to rely on cola de caballo alone.
What’s Inside the Plant
Beyond silica and potassium salts, cola de caballo is rich in a variety of active compounds. The dominant flavonoids in European horsetail are quercetin glucoside, apigenin glucoside, and isoquercitrin. The plant also contains caffeic acid, ascorbic acid (vitamin C), sterols like beta-sitosterol, and several rare acids. Asian and North American varieties have a slightly different chemical profile, containing luteolin compounds not found in European plants. This means the specific effects may vary depending on where the plant was grown.
Safety Concerns and Who Should Avoid It
Cola de caballo is generally well tolerated for short-term use, but there are real risks worth knowing about. The plant contains thiaminase, an enzyme that breaks down vitamin B1 (thiamine) in your body. With long-term use, this can lead to thiamine deficiency, which causes fatigue, nerve damage, and cognitive problems. In one documented case, a woman who took 1,200 mg per day of horsetail for over a year developed B-complex vitamin deficiencies. If you use cola de caballo regularly, taking a B-vitamin supplement is a reasonable precaution.
Certain people should avoid it entirely. Because of its diuretic effect and mineral content, people with heart or kidney disorders, diabetes, or gout should not use horsetail. Women who are pregnant or breastfeeding should also avoid it.
How People Use It
Cola de caballo is most commonly consumed as a tea, made by steeping the dried stems in hot water for 5 to 10 minutes. It’s also available as capsules, liquid extracts, and topical ointments. There is no established standard dose. Product labels vary widely, and clinical studies have used doses ranging from 900 mg per day of dried extract (in the diuretic trial) to topical formulations at 3% to 5% concentration for wound healing. Starting with a low dose and paying attention to how your body responds is the practical approach, since no regulatory body has set an official recommended amount.