Horsetail is one of the oldest medicinal herbs that even precedes dinosaurs on earth. It’s been used to heal ulcers, stop bleeding, treat kidney problems, and fight infections since ancient Greek and Roman times. Horsetail is also a popular source of silica for strengthening bones, hair, and nails. Keep reading to learn about the purported benefits and risks of horsetail use.
What is Horsetail?
Horsetail (Equisetum) got its name due to its resemblance to the tail of a horse.
Out of 15 horsetail species, common horsetail (Equisetum Arvense) is best known for its health benefits. It is native to North America, Europe, the Middle East, and parts of Asia. Other horsetail species are recently gaining popularity around the world. Giant horsetail (Equisetum giganteum) is found only in Latin America .
However, there is insufficient evidence to rate the effectiveness of horsetail for most uses. Proper clinical studies are needed to determine the purported health benefits of horsetail. With this in mind, we’ll discuss the studies that have been published so far and point out the directions future research may take.
Additionally, horsetail supplements have not been approved by the FDA for medical use. In general, dietary supplements lack solid clinical research. Regulations set manufacturing standards for supplements but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
The aerial parts of the plant are used for their health benefits. Ancient Romans used horsetail as food, medicine, and animal feed. In fact, people eat horsetail as a salad in some parts of Europe [2, 3].
Horsetail was historically prepared as a juice, tea, or tincture for treating many diseases. It’s best known in folk medicine for treating swelling, weight loss, diabetes, bladder disease, kidney disease, arthritis, tuberculosis, and other infections .
Components of Horsetail
Horsetail is rich in beneficial compounds that fight inflammation and infections. It also contains vitamins, minerals, and dietary fiber.
- Geographical origin
- Extraction process
- Processing method and storage
Horsetail contains many useful active ingredients:
- Phenolic compounds such as flavonoids and phenolic acids have antioxidant, anti-inflammatory, liver-protecting, antimicrobial, and antitumor effects. These compounds are extremely diverse inactivity and chemistry 
- Silicon and silica boost collagen production, and strengthen hair, bones, teeth, and nails [17, 6, 18, 19, 20, 21]
- Kynurenic acid reduces inflammation and pain [22, 23]
- Styrylpyrones may protect against cancer [24, 25]
- Water-soluble vitamins including ascorbic acid (vitamin C), thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxine (vitamin B6), and folate 
- Fat-soluble vitamins, such as vitamins E and K 
- Trace minerals and other elements like potassium, sodium, calcium, magnesium, iron, zinc, and copper [3, 26]
- Volatile compounds from horsetail essential oils (thymol) have strong antimicrobial effects .
- Inositol 
- Choline 
- Chlorophyll (sometimes removed in extracts), which may prevent cancer, and carotenoids (provitamin A) [3, 28].
- Phytosterols, such as beta-sitosterol and campesterol .
- Dietary fiber 
Mechanism of Action
The source of the medicinal benefits of horsetail come from its silica and antioxidant compounds. They act both alone and together to achieve unique beneficial effects .
Cell-based and animal studies suggest that horsetail may act by*:
- Decreasing inflammation:
- Boosting antioxidant defenses:
- Reducing 5α-reductase: An important enzyme for testosterone production and hair loss in men 
- Increasing the uptake of calcium, remineralizing bones and teeth, and regenerating tissues 
- Increasing the production of collagen, which strengthens and improves the elasticity of the skin, joints, and blood vessels 
- Reducing bleeding and improving wound healing 
- Stopping or slowing down the growth of bacteria, viruses, and yeast by disrupting their cell walls and energy production [27, 43]
*It’s unknown if horsetail acts by the same mechanism in humans. Additional research is needed.
Potential Health Benefits of Horsetail
Insufficient Evidence for:
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of horsetail for any of the below listed uses.
Remember to speak with a doctor before taking horsetail supplements. Horsetail should never be used as a replacement for approved medical therapies.
1) Rheumatoid Arthritis and Osteoarthritis
Horsetail is being researched in people with rheumatoid arthritis. It improved symptoms and regulated the immune response in most cases in a study of 60 patients with rheumatoid arthritis. Horsetail reduced inflammation (increased IL-10 and decreased TNF-alpha), which may be key for treating this disease .
Giant horsetail extract reduced pain, inflammation, and an autoimmune response in a mouse model of rheumatoid arthritis and osteoarthritis. The medicinal benefits of the compounds in horsetail are promising, but more research is needed .
Diuretics are often used to reduce blood pressure and swelling (edema). They work by flushing excessive fluids from the body.
Horsetail extract achieved an effect similar to the standard diuretic in 36 healthy male volunteers, without disrupting the electrolyte balance. We can’t draw any conclusions from this single, small study. Large-scale studies are needed .
Different horsetail species had a strong diuretic effect in mice .
3) Wound Healing
Horsetail has long been used to help heal wounds faster. Horsetail ointment is usually applied directly to the wound.
Horsetail ointment (3%) improved wound healing in a study of 108 healthy women who had surgery to induce childbirth. Half of the women used horsetail ointment on the wound for 10 days, which reduced pain and healed wounds faster, with no side effects. Silica helps to seal the wound, while flavonoids prevent infections .
Additional human studies are needed to determine how safe and effective horsetail preparations are for wound healing.
Horsetail ointment (5% and 10%) increased wound healing in rats after 1 and 2 weeks. The 10% ointment completely healed the wounds and repaired the skin after 2 weeks .
A 5% horsetail ointment healed skin wounds in rabbits after 2 weeks. Horsetail also prevented infection and stopped bleeding .
4) Pain Relief
No other clinical studies have replicated these findings. What’s more, the above study was performed on a very specific population under uncontrolled settings. Until further research is done, the pain-reducing effects of horsetail in humans remain unknown.
Horsetail extract reduced pain and inflammation in mice, with higher doses having a stronger effect .
Traditional Uses Lacking Evidence
Below is a list of the traditional uses of horsetail lacking evidence. Studies do not support the use of horsetail for diabetes, hair loss, skin problems, nail strength, weight loss, liver health, and herpes.
Insufficient evidence supports the traditional use of horsetail for diabetes, though early findings are promising.
In diabetic rats, horsetail extract balanced glucose levels and regenerate insulin-producing cells of the pancreas. Different horsetail extracts reduced blood glucose and normalized weight in rats with diabetes. Some scientists believe horsetail may stimulate or mimic insulin [48, 49].
Hair and Nails
Hair loss in women may be caused by different factors than in men, such as stress, fever, surgery, thyroid problems, and childbirth. Horsetail in combination with other ingredients increased hair growth, volume, and thickness in a study of 15 women with thinning hair .
Evidence is lacking to support the herb’s traditional use for liver problems and hepatitis.
Only one animal study investigated whether high doses of horsetail over 14 days damage the liver in rats. In this study, horsetail did not cause liver damage. Based cellular studies, some scientists think the liver effects of horsetail’s onitin and the flavonoid luteolin should be researched further [52, 53].
Women from Amazonian tribes traditionally used giant horsetail for genital infections and hygiene. Evidence does not support this use.
Future clinical trials should look into the effects of horsetail on herpes. When tested on virally infected cells and in mice, giant horsetail was active against the herpes simplex virus type 2 (genital herpes) and improved symptoms. We can’t draw any conclusions from this small, low-quality animal study .
Effect on Kidney Stones
Although horsetail is traditionally used for kidney stones, no evidence supports it.
Horsetail was only researched in a rat study. It prevented kidney stones and kidney damage in rats in combination with other herbs. It also helped to break down and eliminate kidney stones in rats. Much more research is needed [55, 56].
Some people traditionally use horsetail for weak bones. Research does not back up this use.
Silicon is crucial for forming and maintaining healthy bones. It helps to absorb calcium and improves bone mineralization and structure. Horsetail has a long history of traditional use for bone healing .
Evidence does not support the use of horsetail for skin problems.
Some researchers think horsetail holds promise, though. It’s still far too early to say whether they have a point.
Eczema and acne have many causes, but inflammation is common to both.
Inflammation in eczema causes itchiness, alters the skin barrier, and makes the skin more prone to infections. Acne is mostly caused by bacterial infections.
Horsetail may help treat both acne and eczema. In Japan, horsetail is commonly used in cosmetic products as a cream, lotion, or ointment. Cell studies confirm that essential oils have antibacterial properties and its phenolic compounds reduce inflammation. Horsetail could potentially be utilized as a skin therapy product .
Horsetail is thought to have anti-aging and skin toning properties. Silicon is a component of collagen, which is needed to keep skin elastic and smooth. Since horsetail is rich in silicon, it’s been formulated into various skincare products and cosmetics to promote collagen growth in the skin .
In some countries, horsetail liquor or tea is used as a folk remedy to improve digestion. Flavonoids such as those found in horsetail are being researched for their effects on digestion, bloating, nausea, and stomach pain .
Horsetail acts as a diuretic and reduces fat in rats. Some people think it may supplement a weight loss regime by flushing excessive fluids, decreasing inflammation, bloating, and fat. Horsetail also increases IL-10, which may boost weight loss. But how horsetail affects body weight on its own is still unknown [60, 2, 44, 38, 38].
One strategy for reducing cellulite is to remove built-up fluids from the target area. Horsetail could help fight cellulite by cleansing fluids from the body and toning the skin. Although horsetail products are formulated in Spain for reducing cellulite, no clinical studies have yet confirmed the benefits [2, 61, 62].
Some herbal combinations with horsetail have been used to treat varicose veins. It’s unknown exactly how horsetail acts on varicose veins. Its anti-inflammatory and skin healing properties could be beneficial when used as a cream, lotion, or ointment on affected areas .
Horsetail has been traditionally used to treat gout, due to its anti-inflammatory properties. Gout is a form of inflammatory arthritis. The beneficial effects of horsetail for rheumatoid arthritis could be important for treating gout [62, 38].
Still, no clinical studies have looked at horsetail in gout disease models.
No valid evidence supports the use of horsetail for anxiety, sleep, seizures, brain health, viral infections, ulcers, or any of the conditions listed below.
Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts.
However, the studies listed below should not be interpreted as supportive of any health benefit. Horsetail should not be used for any of the conditions described below due to the complete lack of safety and efficacy data in humans.
Horsetail extract reduced anxiety in mice as strongly as the standard anti-anxiety drug (diazepam), shown in several studies. The anti-anxiety effect of horsetail is attributed to flavonoids, which are now being called the “new benzodiazepines” (anxiety medications) .
In fact, flavonoids may actually achieve calming effects by increasing GABA and other key neurotransmitters in the brain. The effects of flavonoids on the brain may go beyond the simpler mechanism of action of benzodiazepines, though much more research is needed [64, 65].
Relaxation and Sleep
When used in higher doses than for treating anxiety, horsetail increased the duration of sleep in mice. The flavonoid isoquercetin in horsetail acts as a mild and safe sedative. This calming effect opens the door to potential therapeutic use for sleeping problems, and for relaxation before surgery [63, 65, 66].
Horsetail prevented, delayed, and reduced the intensity of seizures in mice. The anti-seizure effect may be due to the flavonoid isoquercetin, but other unknown compounds could also play a role .
The effects of horsetail on the brain are just beginning to be uncovered. Its complex antioxidant composition may protect the brain and improve cognitive function. Antioxidative defenses weaken with aging and may cause dementia, Alzheimer’s disease, and Parkinson’s disease .
Powerful flavonoid antioxidants in horsetail (such as isoquercetin) enhance cognitive function and reverse memory loss. Horsetail used over a longer period of time improved cognition and memory in older rats [68, 64].
Horsetail injections given to rats with nerve injury (sciatica) protected neurons. Horsetail may prevent or delay nerve loss after injury. Silica boosts the nerve-protecting effect and together with antioxidants aids in recovery .
Kaempferol, another flavonoid in horsetail, protects against brain injury and inflammation in rats with stroke. It reduces inflammation in the brain after a stroke by increasing NF-κB and decreasing inflammatory cytokines TNF-Alpha and IL 1-Beta .
However, the effects of horsetail on the brain
Ulcers and Hemorrhoids
Excessive bleeding is common to heavy menstrual periods, hemorrhoids, and ulcers. Researchers are exploring whether horsetail can help reduce bleeding and shrink the size of wounds, which would theoretically help with ulcers and hemorrhoids. However, evidence to support its use for these health problems is completely lacking at the moment .
Isoquercetin, an active ingredient of horsetail, reduced flu symptoms in mice .
In cells, isoquercetin kills influenza A and B viruses – the most common viral strains that cause the flu. Horsetail is rich in isoquercetin and fights many viruses, but only isoquercetin was tested against these flu strains .
Phytosterols and flavonoids in horsetail may be able to alleviate this. Phytosterols reduced LDL cholesterol and antioxidants decreased inflammation in cells. High LDL cholesterol and inflammation can cause hardening of the blood vessels and heart problems [78, 79, 32, 80].
After menopause, hormone changes can cause an increase in fat, making women more prone to heart disease. Horsetail reduced fat levels in postmenopausal rats .
Some scientists think horsetail may carry the potential to prevent heart disease in women going through menopause .
Chemotherapy Side Effects
Researchers are exploring whether horsetail can help reduce the side effects of chemotherapy or boost the action of cancer drugs. Horsetail reduced the toxic effects of cyclophosphamide (a drug used to treat different types of cancer) in mice .
Histamine narrows airways in asthma, causing difficulty breathing and mucus buildup. Horsetail blocks the effects of histamine, relaxing airways in a study in rabbit airway tissues. Higher doses of horsetail had a stronger effect .
Active compounds in horsetail slow down bowel movements during diarrhea. Compounds in horsetail block acetylcholine, which is a neurotransmitter that promotes bowel movements. In a study on rabbit and guinea pig gut tissue, horsetail relaxed stomach muscles and reduced cramps in diarrhea .
Horsetail reduced an overactive immune response in human cells. Horsetail causes cells to produce less inflammatory molecules (IL-2 and TNF alpha) and the silica balances the immune effect in these cells. Higher concentrations of the herb have a stronger effect .
The combination of active ingredients in horsetail can fight many bacterial, viral, and yeast infections .
Horsetail is being investigated for fighting respiratory, genital, and urinary infections. It may stop the growth of harmful bacteria and viruses when applied to wounds, but the evidence is insufficient. When used in shampoo, it may reduce dandruff [4, 84, 27, 85].
Kaempferol is one of the ingredients in horsetail that kills microbes .
- Staphylococcus aureus, a bacteria resistant to many antibiotics. It commonly causes skin and respiratory infections and food poisoning
- Escherichia coli, which causes urinary tract infections (UTIs), diarrhea, and inflammatory bowel disease. Horsetail slows the growth and activity of this bacteria, which may justify its traditional use for UTIs
- Klebsiella pneumoniae, which may cause respiratory infections such as bronchitis and pneumonia
- Pseudomonas aeruginosa, a bacteria resistant to most antibiotics that can cause life-threatening drug-resistant infections
- Salmonella, which causes food poisoning
Cell-Based Cancer Studies
Horsetail is being researched for its effects on skin, blood, and lung cancer in cells. Some scientists think antioxidants in horsetail and zinc in horsetail may aid cancer prevention, though their hypothesis has not been proven. Many substances can “kill cancer” in cells, but that says nothing about their actual cancer-fighting potential [78, 86, 87, 88, 89].
Dental cavities are usually caused by bacteria. Horsetail improves oral health by destroying bad bacteria. It may improve gum inflammation and bleeding (gingivitis). Horsetail could even be used as a homemade mouthwash [90, 9].
Oral candida is a yeast infection that can be caused by dentures, a weakened immune system, and antibiotics. Giant horsetail was active against oral candida; common horsetail essential oil also fights this yeast [27, 91].
Horsetail Risks and Safety
Thiaminase and other Alkaloids
Horsetail is generally safe, and short-term use is not associated with side effects. Horsetail does carry some risks and is not safe to use in some populations .
- Marsh horsetail (Equisetum palustre) causes poisoning in livestock. It contains highly toxic alkaloids and thiaminase. Thiaminase breaks down thiamine (vitamin B1) and causes serious symptoms of vitamin deficiency. Avoid marsh horsetail supplements, and buy horsetail from a reliable manufacturer [92, 93].
- Quality manufacturers will ensure horsetail supplements do not contain thiaminase (“thiaminase-free” products). But it’s still possible that the enzyme has not been completely removed. People with low thiamine should avoid horsetail or take special precaution .
Thiamine deficiency can be suspected in:
- Alcohol abuse
- Liver disease
- Some brain disorders
- Genetic disorders
- Avoid drinking alcohol on a regular basis when taking horsetail to reduce the risk of thiamine deficiency.
- Common horsetail can contain traces of nicotine. People using nicotine patches or nicotine chewing gum should avoid horsetail .
- Horsetail can reduce blood glucose levels. People with diabetes should regularly monitor their glucose levels if taking horsetail .
- Long-term use of oral horsetail supplements is not recommended, as no long-term safety studies exist.
- Horsetail may cause skin allergies. Rats fed large amounts of horsetail on a cholesterol-rich diet developed a skin allergy .
- One case of hepatitis was reported after a male took horsetail tea for a week .
- Pregnant and breastfeeding women, as well as children (age < 18 years) should not use horsetail due to lack of safety data.
- Horsetail increases the elimination of potassium due to its diuretic effect. This can cause low potassium levels. Horsetail should not be used in people with a risk of potassium deficiency or in people with heart arrhythmias .
- People with allergies to carrots and nicotine: Some people with an allergy to carrots or nicotine might also be allergic to horsetail and should avoid it.
Several prescription medications may interact with horsetail :
- Lithium: Horsetail could interfere with lithium elimination and cause a dangerous buildup
- HIV medications: Horsetail may cause worsening of HIV if taken with HIV drugs
- Diuretics (water pills)
- Digoxin (for heart failure)
- Phenytoin (anti-seizure)
- Anti-diabetes drugs
Additionally, horsetail contains chromium (0.0006%). It may increase the risk of chromium poisoning when taken with chromium supplements or chromium-containing herbs such as bilberry, brewer’s yeast, or cascara.
Consult your healthcare provider before taking horsetail or any other supplement if you are on prescription medications. Drug interactions can lead to serious adverse events.
Forms of Supplementation
Horsetail is usually used in the following forms:
- Fresh/dried herb
- Essential oil
- Cream, lotion, ointment, and powder for hair/skin use
Choosing a horsetail supplement depends on the sought-out health benefits. Standardized extracts are usually of higher quality and have a specified amount of the active ingredient. At least 0.3 % of total flavonoids should be present in the dried plant, standardized to isoquercetin .
Tea seems like the easiest and least expensive solution. But, water does not extract some active ingredients as well as other solvents (like alcohol). Tea will have the mildest effect and the lowest concentration of antioxidants .
- Extracts: 900 mg per day of the dried extract of common horsetail standardized to 0.026% total flavonoids was used for diuretic effects in healthy volunteers. The daily dose was split up to 300 mg 3 times in a day .
Otherwise, the dosage is based on traditional use. Most supplements contain 300 mg dried extract per capsule/tablet, and depending on the extract type, can usually be used up to 3 times daily [99*].
The daily dose for most alcohol extracts based on traditional use is 2 to 12 ml per day (depending on the extract type) [99*].
- Tea: 1 to 4 g of the dried herb can be used to make tea, to be taken 3 to 4 times daily over 2 to 4 weeks (based on traditional use) [99*].
- Ointment: A sterile 3% common horsetail ointment helped wound healing and reduced pain after surgery in one study .
*According to the European Union herbal monograph on horsetail prepared by the Committee on Herbal Medicinal Products.
Horsetail in Combination with Other Supplements
- A combination of horsetail with L-lysine, L-proline, L-arginine, and vitamin C was used in one study to prevent and treat osteoporosis in aged female rats who don’t produce estrogen. It boosted collagen production, bone development, and strength. Osteoporosis is common in women after menopause, as estrogen production decreases .
- A combination of horsetail, soy isoflavones, vitamin D3, and lactoferrin improved osteoporosis in aged rats. It had no effect on younger rats .
- Nourkrin is a supplement for treating hair loss that contains horsetail, fish proteins, acerola cherry, silica, and D-biotin. It improved hair loss after 6 months in a study with 55 men suffering from hair loss .
- Viviscal is an oral supplement for treating hair loss containing silica from horsetail, fish extract, biotin, zinc, vitamin C, and iron. It increased hair growth, volume, and thickness in women with thinning hair after 3 months. Viviscal achieved similar results in a study with men experiencing hair loss [51, 103].
- Eviprostat used to treat enlargement of the prostate (benign prostatic hyperplasia – BHP), contains common horsetail, prince’s pine, aspen, small pasque flower, and purified wheat germ oil. Eviprostat has been used in Japan and Germany for over 40 years .
- Eviprostat also shows anti-inflammatory and antioxidant activity. Eviprostat reduced oxidative stress in 9 patients with BHP. In an open clinical study of 100 patients with BHP, it reduced symptoms and improved quality of life. Eviprostat improved prostate inflammation and pain in 50 patients with prostate inflammation [ 104, 105, 106, 107].
Kidney and Bladder Support
- A herbal combination with common horsetail, verbena, gromwell, dandelion, bearberry, greater burdock, and Silene saxifraga was used to treat kidney stones in rats .
- Herbensurina used to prevent treat kidney stones in rats contains horsetail, smooth rupturewort, couch grass, and elderberry .
- Urox is a supplement for bladder support that contains horsetail, varuna, and lindera plant extracts. It reduced overactive bladder and urinary incontinence in a study with 150 participants. Urox reduced symptoms of urgency, frequency, incontinence, and nighttime urination after 8 weeks .
- A Japanese herbal patent for reducing cavities and bad breath contains horsetail as one of the ingredients. The herbal combination may act by blocking an important enzyme. More studies would need to tease out the benefits of horsetail in the combination .
- Nail polish containing horsetail, hydroxypropyl-chitosan, and methylsulfonylmethane improved nail psoriasis on all fingernails after 6 months in a study of 87 patients with psoriasis. Psoriasis is a chronic inflammatory skin disease, and half of the people suffering from it will also experience nail damage .
Limitations and Caveats
It’s still questionable exactly which active ingredients carry the benefits of horsetail. Extracts should be standardized to the flavonoid isoquercetin, but some manufacturers emphasize silica content. Although many other ingredients have health benefits, their concentration in various supplements is uncertain .
Studies used different species of horsetail. Determining the most beneficial species and extract type would be helpful.
Clinical studies are rare, and most of them have a small sample size.
Currently, there is insufficient evidence to support the purported health benefits of horsetail listed in this article. Proper, large-scale, double-blinded, randomized clinical trials need to be carried out to determine the effectiveness and safety of various horsetail preparations.
Additionally, it’s hard to tease apart the effect of horsetail when other herbs/nutraceuticals are used in the study.
Some studies were only done on cells. Many studies show positive findings in cells but fail to have any effect in animals or humans. Some compounds that show promising results in animals turn out to be ineffective or dangerous in humans. Thus, cell studies cannot be used to draw any health-related conclusions.
Additionally, cell studies provide no clues about the amount of active substances that might be absorbed in animals or humans. For example, some silicon in horsetail is bound to oxygen in the form of silica, which makes it harder to absorb.
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Many users said horsetail capsules helped them regrow thinning hair or strengthen hair and nails, usually in combination with other supplements and stress reduction.
One user reported eliminating kidney stones after drinking horsetail tea for a month instead of water.
Another user didn’t notice improvement after taking horsetail powder for 6 months to regenerate knee meniscus damage.
Some users experienced stomach burning and cramps after taking horsetail over 2 to 4 weeks for hair, skin, and nails. The burning went away once horsetail was discontinued. One user mentioned experiencing similar symptoms with other hair supplements with high silica content.