Horsetail is one of the oldest medicinal herbs that even precedes dinosaurs on earth. People used it to heal ulcers, stop bleeding, remedy kidney problems, and fight infections back in ancient Greek and Roman times. As a source of silica, horsetail is also claimed to strengthen bones, hair, and nails. Read on to find out which of these purported benefits are supported by science.
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 .
Horsetail is being studied for bone, oral, hair, and nail health. This is because horsetail is actually the most abundant source of silica in the plant world [5, 6, 4, 7, 8, 9].
Horsetail ointment can be applied to heal wounds, stop bleeding, prevent infection, and reduce pain .
Purported 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
Horsetail ointment (3%) reduced pain in a study with 108 healthy women shortly after giving birth. Half of them used horsetail ointment on a surgical wound for 10 days .
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 .
Insufficient evidence supports the traditional use of horsetail for diabetes, though early findings are promising.
In 11 patients recently diagnosed with type 2 diabetes, a single oral dose of horsetail extract reduced blood glucose within 1.5 hours. No conclusions can be drawn from this study .
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 [17, 18].
6) Hair and Nails
Horsetail has high silicon and antioxidant content, but its use for hair and nails is not sufficiently backed up by research [19, 20].
Also, silicon shouldn’t be confused with silicone, which is the synthetic substance used in plastic surgery and the electronics industry! Silicon, on the other hand, is a natural chemical element.
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 .
Uses Lacking Evidence:
Below is a list of horsetail’s traditional uses and experimental findings (from animal and cell-based research) lacking clinical evidence.
These data should guide further investigational efforts.
However, the studies listed below should not be interpreted as supportive of any health benefit due to a lack of safety and efficacy data in humans.
Thus, studies do not support the traditional use of horsetail for weight loss, liver health, and herpes.
No clinical evidence supports the experimental use of horsetail for anxiety, sleep, seizures, brain health, viral infections, ulcers, or any of the conditions listed further below.
7) Liver Health
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 [22, 23].
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 .
9) 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 [25, 26].
10) Bone Health
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 .
Horsetail increased the activity of human bone cells, crucial for bone regeneration. Horsetail extract increased bone cell growth while killing bacteria that can cause bone infection [6, 28].
11) Skin Health
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 .
13) Weight Loss
Giant horsetail is a popular weight loss supplement in Latin America .
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 [32, 2, 12, 10].
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, 33, 34].
15) Varicose Veins
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 [34, 10].
Still, no clinical studies have looked at horsetail in gout disease models.
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 [36, 37].
18) 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 [35, 37, 38].
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 [40, 36].
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
21) 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 .
Only one study showed that horsetail-extract reduced stomach ulcers in rats. It improved symptoms, protected the stomach, and prevented further damage [44, 45, 46].
22) Flu Symptoms
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 .
23) Heart Health
Horsetail relaxes blood vessels, and reduced blood pressure in rats with heart disease. Dicaffeoyl-meso-tartaric acid is the active ingredient in this process [48, 49].
Horsetail reduces fat oxidation, which is often the underlying cause of heart disease .
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 [50, 51, 52, 53].
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 .
24) 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 .
28) Bacterial Infections
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, 58, 29, 59].
Kaempferol is one of the ingredients in horsetail that kills microbes .
Horsetail essential oil contains 25 compounds that were researched against the following bacteria [29, 58]:
- 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
29) 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 [50, 60, 61, 62, 63].
30) Oral Health
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 [64, 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 [29, 65].
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.
Horsetail has been used since ancient times as both food and herbal remedy.
However, there is insufficient evidence to support any of the purported benefits of this herb.
Research reveals that horsetail is high in silica, which the body uses to produce collagen. Hence, horsetail is now being studied for its effects on bone, skin, and hair health.
Traditional horsetail uses — such as for reducing water retention, kidney or heart problems, and infections — still remain unproven.
Lastly, horsetail is not safe for everyone and it can interact with medications. Speak to your doctor before supplementing.