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Organic Horsetail Herb

Also known as: Horsetail, bottlebrush, shavegrass, field horsetail, Equisetum hyemale, Equisetum arvense

Overview

Horsetail (*Equisetum arvense*) is a perennial fern-like plant widely distributed globally, primarily in moist environments. The above-ground parts of the plant are traditionally harvested for medicinal purposes. Historically, it has been used as a diuretic, anti-inflammatory agent, and for wound healing. Contemporary interest in horsetail centers on its high silica content, which is believed to support the health of hair, skin, and nails, as well as potentially contributing to bone health and providing antioxidant effects. The plant is rich in various compounds including silica (as silicic acid), flavonoids, phenolic acids, saponins, and alkaloids. While preclinical studies suggest antioxidant and antimicrobial properties, human clinical trials are limited, often small, and frequently involve multi-ingredient formulations, making it challenging to definitively attribute benefits solely to horsetail.

Benefits

The evidence for specific benefits of horsetail in humans is generally weak and based on low-quality research. No robust, adequately powered randomized controlled trials (RCTs) have demonstrated clear, statistically significant benefits for primary health outcomes. A 3-month study involving women with self-perceived hair thinning reported increased hair growth and strength with a multi-ingredient supplement containing horsetail; however, the isolated effect of horsetail could not be determined. Preclinical studies (in vitro and animal models) suggest potential antioxidant, anti-inflammatory, and antimicrobial effects, but these findings have not been reliably translated to human outcomes. Similarly, in vitro and animal studies indicate a potential role for horsetail's silica content in bone health, but human data are lacking. There is no high-quality evidence to support population-specific benefits, and any reported benefits are of uncertain clinical significance due to study limitations.

How it works

Horsetail's proposed mechanisms of action are primarily attributed to its rich silica content and various phenolic compounds. Silica is believed to be incorporated into connective tissues, such as hair, skin, nails, and bone, potentially supporting their structural integrity and collagen synthesis. The flavonoids and phenolic acids present in horsetail are thought to exert antioxidant activity by scavenging free radicals and reducing oxidative stress. Additionally, some compounds may contribute to anti-inflammatory effects through the modulation of immune cells. In high doses, horsetail's thiaminase content can interfere with thiamine (Vitamin B1) metabolism, potentially leading to thiamine deficiency. While silica from horsetail is considered bioavailable, the exact absorption rates and specific molecular targets in humans are not well characterized.

Side effects

Horsetail is generally considered safe for short-term use in most adults, but comprehensive safety data are limited. Common side effects are not well documented in controlled studies, though anecdotal reports include gastrointestinal upset. Uncommon side effects, reported in case studies, include thiamine deficiency (due to the enzyme thiaminase), hypokalemia (low potassium levels), and hypoglycemia, particularly in individuals with diabetes. Rare but serious side effects have been reported, such as acute hepatocellular liver injury, including jaundice and elevated liver enzymes. However, these cases often involve confounding factors like pre-existing hepatitis B, complicating the assessment of direct causality. Horsetail can interact with medications, potentially enhancing the effects of diuretics, leading to electrolyte imbalances, and increasing the risk of low blood sugar when taken with hypoglycemic agents. It is contraindicated during pregnancy, breastfeeding, and in individuals with thiamine deficiency, kidney disorders, or diabetes (unless under strict medical supervision). Due to insufficient safety data, it should be avoided in children and individuals with liver or kidney disease.

Dosage

There is no established minimum effective dose or optimal dosage range for horsetail supported by rigorous human trials. Traditional uses often involve 1–4 grams of dried herb daily, but this lacks clinical validation. A maximum safe dose has not been determined, and long-term use is generally discouraged due to the risk of thiamine deficiency. There is no evidence to suggest optimal timing for administration. Horsetail is available in various forms, including dried herb, teas, extracts, and capsules, with silica content varying by preparation method. The absorption and bioavailability of silica from horsetail are not well studied, though hot water extraction may influence silica availability. No specific cofactors are established, but thiamine supplementation may be prudent with prolonged use due to the thiaminase content.

FAQs

Does horsetail really help with hair growth and nail strength?

While horsetail is often marketed for hair and nail health due to its silica content, human evidence is weak. Most studies involve multi-ingredient supplements, making it difficult to attribute benefits solely to horsetail. High-quality research is lacking.

Is horsetail safe to take?

Horsetail is likely safe for short-term use in healthy adults. However, it should be avoided by pregnant or breastfeeding women, children, and individuals with kidney or liver disease, diabetes, or thiamine deficiency due to safety concerns and lack of data.

What are the main risks or side effects of horsetail?

Key risks include thiamine deficiency, low potassium, and low blood sugar, especially with prolonged use or in susceptible individuals. Rare cases of liver injury have been reported. It can also interact with diuretics and diabetes medications.

How should I take horsetail, and what is the recommended dose?

There is no scientifically established optimal dose or timing for horsetail. Traditional doses range from 1-4g of dried herb daily, but this is not clinically validated. Consult a healthcare professional for guidance.

Can horsetail interact with my medications?

Yes, horsetail can interact with certain medications. It may enhance the effects of diuretics, potentially leading to electrolyte imbalances, and can increase the risk of low blood sugar when taken with hypoglycemic agents for diabetes.

Research Sources

https://www.ncbi.nlm.nih.gov/books/NBK583202/ – This case report details a 52-year-old male who developed acute hepatocellular jaundice and liver injury after consuming horsetail juice for 15 days. Liver enzymes and bilirubin were significantly elevated, improving after discontinuation. The report notes that pre-existing hepatitis B might have contributed to the severity, highlighting a potential risk of liver toxicity, especially in vulnerable individuals.
https://pmc.ncbi.nlm.nih.gov/articles/PMC8281430/ – This review article summarizes the potential benefits and risks of horsetail. It discusses proposed antioxidant, antimicrobial, and anti-inflammatory effects based on preclinical data, while also outlining risks such as thiamine deficiency, hypoglycemia, and hypokalemia. The review emphasizes the lack of rigorous human trial data and the reliance on in vitro and animal studies for many claims.
https://www.healthline.com/nutrition/horsetail – This article provides an overview of horsetail, discussing its traditional uses and modern applications, particularly for hair, skin, and nail health due to its silica content. It acknowledges the limited human clinical trial data, often involving multi-ingredient formulations, which makes it difficult to isolate horsetail's specific effects. It also touches upon potential side effects and safety considerations.
https://www.health.gov.au/sites/default/files/2025-04/whm_abc_final.pdf – This document, likely from a government health authority, provides a general overview of herbal medicines, including horsetail. It likely discusses the plant's traditional uses, active constituents, and highlights the need for caution due to limited high-quality human evidence and potential safety concerns, aligning with the broader consensus on horsetail's research maturity.