What Is Horsetail?

Horsetail (Equisetum arvense) is an herb in the Equisetaceae family of plants, which have been used since ancient Greek and Roman times. Traditionally horsetail has been used as a medicinal herb to treat osteoporosis, tuberculosis, and kidney problems.

Horsetail was also used as a diuretic (for relief of fluid retention) and to stop bleeding and heal wounds. However, there are very few reliable research studies available to solidify the claims that horsetail is safe or effective for use as a medicinal herb.

The perennial plant, sometimes considered a weed, spreads quickly and can rapidly invade a garden, or other moist habits. The fern-like horsetail plant, with hollow, pointed stems and scaly leaves, grows to about 12 inches tall. Only the green fern-like part of the plant is used for medicinal purposes; the root is not used.

What Is Horsetail Used For?

Although there is not enough clinical research data to back the claims of the touted health benefits of horsetail, the plant has been used to treat many conditions, including:

• Bleeding
• Gout
• Frostbite
• Heavy menstrual periods
• Incontinence (inability to control the bladder)
• Kidney or bladder stones
• Osteoarthritis
• Urinary tract infections
• Weight loss
• Wounds

Studies

Osteoporosis involves softening/thinning of the bone tissue; this often occurs in menopausal women. Horsetail contains silicon, a mineral needed for healthy bone and connective tissue production. This is the reason that horsetail has been used to treat osteoporosis in menopausal women.  

A 2016 animal study published in the Indian Journal of Pharmacology found calcium, vitamin D, zinc -lysine, L-proline, L-arginine, and L-ascorbic acid (N) accelerate the mineralization of bone matrix and bone formation and adding a horsetail extract was beneficial for bone formation. 

More research studies (particularly studies involving humans) are needed to prove the efficacy of horsetail in the treatment of osteoporosis.

In an animal study published by the Pakistan Journal of Biological Sciences, the study authors explain that horsetail may have a significant antidiabetic effect stating that more studies are needed to identify exactly how Equisetum arvense (horsetail) works to lower blood sugar.

How Does it Work?

The chemicals in horsetail are thought to have anti-inflammatory (reducing inflammation) and antioxidant (chemicals that help boost the immune system) properties. 

Horsetail contains silica and silicon, minerals that work together to strengthen the hair and nails, as well as promoting healthy bone tissue. Selenium is also found in horsetail; this is a mineral, known to help the hair grow.

Possible Side Effects

Horsetail is listed by the FDA (Food and Drug Administration) as being an herb of undefined safety according to DailyMed. 

Special Warning

Horsetail may be unsafe when taken long-term because of an enzyme contained in the herb, called thiaminase. This enzyme breaks down thiamine (vitamin B1), rendering it useless. An abundance of could result in thiamine deficiency.

Contraindications

Contraindications are situations (including treatments, other drugs, or illnesses) in which a specific medication or herbal supplement should not be used. Horsetail is contraindicated for those who have these conditions:

• Alcohol use disorders: Horsetail decreases the body's ability to use thiamine and excessive alcohol intake increases the risk of thiamine deficiency
• Pregnancy or breastfeeding: There is not enough clinical research evidence to prove the safety of the use of horsetail during pregnancy or breastfeeding.
• Diabetes: Horsetail is thought to lower blood sugar and can result in dangerously low blood sugar levels in diabetics
• Thiamine deficiency: Horsetail breaks thiamine in half, rendering it ineffective in the body, which can lead to thiamine deficiency
• Hypokalemia (low potassium level): Horsetail’s diuretic (fluid flushing) effect may remove too much potassium from the body as it flushes fluids, leading to worsening of low potassium levels

Drug Interactions

Horsetail should not be taken with:

• Lithium: The diuretic effect of horsetail may interfere with the rate at which lithium is excreted from the body, this could result in a change in lithium levels (potentially causing serious side effects).
• Diabetic drugs such as Amaryl (glimepiride), glyburide, insulin, pioglitazone, rosiglitazone, Diabinese (chlorpropamide), Glucotrol (glipizide), Orinase (tolbutamide), and more. Because horsetail has been found to lower blood sugar taking the herbal supplement with insulin, or other diabetic drugs could result in dangerously low blood sugar levels.
• Diuretics (water pills), particularly those that decrease potassium, such as Diuril (chlorothiazide), Thalitone (chlorthalidone), Lasix (furosemide) and hydrochlorothiazide (HCTZ). A small randomized double blind study found that horsetail was as effective as for its diuretic effects.
• Nicotine patches or nicotine gum: Horsetail also contains nicotine, therefore it should not be taken when chewing the gum or using nicotine replacement patches.
• Lanoxin (digoxin): Those with heart irregularities (arrhythmias), as well as people taking digoxin, should not take horsetail, due to the herb's ability to lower potassium levels (which may impact how regularly the heart beats and worsen cardiac arrhythmias).

Over-the-counter drugs, natural supplements, and vitamins can also interact with herbal supplements such as horsetail. Always use caution and follow the healthcare providers recommendation on the use of horsetail and all other medicinal herbs.

Selection, Preparation, & Storage

Medicinal preparations made with horsetail from Equisetum are usually considered safe, however, another species of horsetail, named Equisetum palustre was found to be poisonous to horses.

Preparation

Horsetail is available as a dried herb to use in tea and other mixtures as well as a liquid form. Capsules and tinctures are also available.

Just as with all other herbal supplements and drugs, the dose of horsetail depends on many factors, including a person’s age, health status, and more. These factors have not been studied enough to come up with a safe and effective dose when taking horsetail. 

Be sure to follow the instructions of the naturopath, pharmacist, physician or other healthcare professional, and always read and follow the package insert/label regarding dosage.

Regardless of the reports of toxicity surrounding horsetail, some herbal experts still recommend its use. For example, James A Duke, Phd. 

The average dose of horsetail depends on the condition that is being treated, average doses may include:

• Brittle nails: A specific type of topical formulation (including horsetail and other chemical elements) applied every night for 29 days (or every other day for 14 days) in clinical trials.
• Diuretic: A dry extract of horsetail containing 0.026% total flavonoids was given as a 300 mg dose, by mouth three times per day.
• Wound healing: A 3% horsetail ointment was applied to the episiotomy site in postpartum mothers every 12 hours for 10 days.

Penn State Hershey dosages of horsetail include:

• A capsule: The standard dose has 10% to 15% silica
• An herbal infusion: 2 to 3 teaspoons of dried horsetail, three times per day
• A tincture: Ratio should be 1-to-5 (dosage should be determined by a healthcare provider)
• A compress (for wounds or skin treatment): 10 grams of herb per 1 liter (33.8 ounces) of water per day

Storage

All preparations should be kept in a sealed dark container and protected from exposure to light.

Other Questions

Is it safe to eat horsetail?

There are two spring harvest offerings from the horsetail plant; these include the fertile tan-colored shoots that appear in the early season—these are edible.

The young, tan-colored shoots were traditionally eaten by Native Americans and the Japanese, but the safety of ingesting the plant has not been proven. The green stalks that appear later can be used for medicinal purposes, but they are not edible.

Can horsetail promote hair growth for everyone?

Horsetail has not been proven to grow hair, but the herb is thought to replenish the minerals in the diet (such as selenium) which are known to promote healthy hair growth. 

However, the use of nutritional supplements is not known to be effective for everyone, in fact, there is limited research available on dietary supplementation and loss of hair. 

Despite the lack of research data, many hair loss products have “active ingredients’’ that include selenium. It’s important to note that selenium toxicity is well documented and one side-effect of taking too much selenium is hair loss. 

Is horsetail safe for children to take?

No. Horsetail has traces of nicotine and is not recommended for kids.

Where does it name come from?

The word "Equisetum" comes from the Latin words “equus” meaning horse and “seta” meaning bristle. This name was derived from the bristle-like properties of the leaves of the horsetail plant, thus its common name, “bottle brush.”

Do note that it is a different plant from Callistemon, which has bristly red flowers that look like a bottle brush.

A Word From Verywell

Horsetail is an herb that may have some beneficial medicinal properties, but it should be used with caution. Not only are there concerns about the safety and effectiveness of horsetail, taking the herb by mouth may deplete the body’s level of thiamine (B1). 

Those who do take horsetail daily should take a quality B complex or multivitamin daily. As with all other herbal supplements, only use horsetail under the supervision of your healthcare provider.