What Is Horsetail?

Horsetail dried herb, capsules, liquid

Verywell / Anastasia Tretiak

Horsetail (Equisetum arvense) is an herb in the Equisetaceae family of plants. It's also called "bottle-brush" or "horse herb."

People have been using horsetail since ancient Greek and Roman times. The plant has been used as a medicinal herb to treat bone loss (osteoporosis), tuberculosis, and kidney problems. Some have claimed that horsetail can help relieve fluid retention (diuretic), stop bleeding, and heal wounds.

While it has been used for a long time, there is no good research on how well horsetail works or how safe it is for humans. This article will go over what studies have found about using horsetail. It will also teach you about how horsetail has been used and what you should know before trying it.

All About Horsetail

Horsetail is a perennial plant. That means it comes back every year and usually lives at least two years. It is considered a weed because spreads quickly. The plant is invasive, meaning that it can move through an area of land very fast. For example, it can be hard to get rid of once it's in your garden.

The horsetail plant is like a fern. It has hollow, pointed stems and scaly leaves. Horsetail grows to be about 1 foot tall (12 inches).

Only the green fern-like part of the plant is used for alternative medicine purposes. The root of the plant is not used.

What Is Horsetail Used For?

In alternative medicine, herbs like horsetail have been used for many thousands of years to treat health problems. However, there is not enough research on horsetail to know if it will help these conditions. It's also not clear if it's safe for humans to use.

Here are a few examples of conditions that some people claim horsetail may help:

Research on Horsetail

Products that have horsetail in them may claim to help or even treat medical conditions. However, there is not enough research to support the claims. The research on horsetail that has been done was mostly in animals, not people. The results of those studies could help us learn about horsetail but do not necessarily apply to humans.

Here are a few studies that have looked at how horsetail could be used for health problems.

Osteoporosis

Osteoporosis is a condition that causes softening or thinning of the bone tissue. It often occurs in people who are going through menopause. Horsetail contains silicon, a mineral needed for healthy bone and connective tissue production.

Some studies have looked at whether horsetail can help treat osteoporosis, but they were not done in people. Instead, the researchers used animals who had their ovaries taken out. That made them similar to a person who is in menopause.

For example, a 2016 study published in the Indian Journal of Pharmacology found that calcium, vitamin D, zinc -lysine, L-proline, L-arginine, and L-ascorbic acid (N) helped bones form faster in rats. Adding a horsetail extract to the treatment seemed to help with bone formation.

The study only looked at bone formation in rats. It's not clear if the same benefits would happen in humans with osteoporosis.

Hair Growth

Horsetail has an amino acid called cysteine in it. The herb also contains minerals such as selenium, which is known to enhance hair growth.

Blood Sugar

Another study in rats that was published by the Pakistan Journal of Biological Sciences found that horsetail may help lower blood sugar (glucose) levels. However, because the study was done using animals, more research needs to be done with humans to see if it would help and be safe to use.

Recap

Horsetail has been said to help with health problems like weak bones and hair loss. However, there is not enough research showing it is safe and effective for humans to use. Most of the studies that have been done were on animals, not people.

How Does Horsetail Work?

Certain chemicals in horsetail are thought to lower inflammation. They might also help the body make more substances that boost the immune system (antioxidants).

Horsetail also has silica and silicon in it. These minerals work together to strengthen the hair and nails. They also help the body make healthy bone tissue.

Selenium, another mineral that has been shown to help hair grow, is also found in horsetail.

Possible Side Effects

The Food and Drug Administration (FDA) says that horsetail is an herb of undefined safety. That means that there is not enough research evidence to prove that horsetail is safe to use or that it works for treating health conditions. The FDA has not approved horsetail for any use.

Special Warning

Horsetail has an enzyme called thiaminase in it. The enzyme breaks down thiamine, which is also called vitamin B1. When thiamine is broken down, it becomes useless to the body.

If you take too much horsetail or take it for a long time, you might not have enough thiamine in your body (thiamine deficiency).

Not FDA Approved

Some commercial horsetail products say that they do not have thiaminase in them. However, herbal supplements are not regulated by the FDA. That means the information on these products' labels can be wrong. 

Even if a product does not have thiaminase in it, there is not enough evidence to prove that using a thiaminase-free horsetail product is safe and effective.

Contraindications

A contraindication means that you should not take a medication or supplement because it might cause a bad reaction. Medical conditions, medications, other products you use, and treatments can all be contraindications.

Horsetail has several known contraindications. If any of these situations apply to you, do not use horsetail.

  • Alcohol use disorders: Horsetail makes the body less able to use thiamine. Drinking a lot of alcohol can make you more likely to have a thiamine deficiency.
  • Thiamine deficiency: Horsetail breaks thiamine in half. This makes it useless in the body. If this happens, you may not have enough thiamine to meet your body's needs (thiamine deficiency). Your provider might want you to take a B complex or multivitamin daily if you use horsetail to help prevent a thiamine deficiency.
  • Pregnancy or breastfeeding: There has not been enough research on using horsetail when you are pregnant or breastfeeding to show that it is safe.
  • Diabetes: Horsetail is thought to lower blood sugar. Having blood sugar levels that are too low is called hypoglycemia. If a person with diabetes gets very low blood sugar levels, it can be life-threatening.
  • Low potassium: Horsetail has a "fluid-flushing" effect. This is called a diuretic. When you lose a lot of fluid from your body, you also lose an important nutrient called potassium. If your levels of potassium get too low, it's called hypokalemia. This condition can be very dangerous because it can make your heart not work properly.

Talk to Your Doctor

Always talk to your doctor before taking any herbal supplement—especially if you take any prescription medications. Over-the-counter drugs (OTC), other natural or herbal supplements, vitamins, and minerals can also interact with horsetail.

Drug Interactions

If you are taking certain medications, horsetail could affect how they work. You should not use horsetail if you are taking:

  • Lithium: The "fluid-flushing" effect of horsetail can change how fast lithium leaves your body. If this happens, you might not have the right amount of lithium in your body. This could cause side effects or make the medication not work right.
  • Diabetic drugs: Actos (pioglitazone), Amaryl (glimepiride), Avandia (rosiglitazone), Diabeta (glyburide), Glucotrol XL (glipizide), insulin, and other medicines used to treat diabetes should not be taken with horsetail. Horsetail might lower your blood sugar levels. If you take it with insulin or other diabetic drugs, you could get dangerously low blood sugar levels.
  • Diuretics: Medications (sometimes called "water pills") that "flush" fluid from your body can also make your potassium levels low. Examples of these medications are Diuril (chlorothiazide), Lasix (furosemide), Microzide (hydrochlorothiazide), and Thalitone (chlorthalidone). A small randomized, double-blind study found that horsetail also had a fluid-flushing effect. If you use horsetail with another fluid-flushing medication, your potassium levels might get too low.
  • Nicotine patches or nicotine gum: Horsetail has nicotine in it. You should not use horsetail if you use nicotine gum or nicotine replacement patches.
  • Lanoxin (digoxin): If horsetail lowers your potassium levels, it can affect the beating of your heart. People who already have problems with how their heart is beating (arrhythmia) or take a medication called digoxin should not take horsetail.

Recap

Horsetail is not safe to use if you have certain medical conditions. You also should not mix it with certain medications or other supplements. Always ask your provider before taking herbal supplements.

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.

Horsetail dried herb
Verywell / Anastasia Tretiak

Preparation

Horsetail comes as a dried herb. You can use it as tea and in other mixtures. You can also get horsetail in a liquid, a concentrated liquid called a tincture, or in a capsule.

Here are a few examples of the doses of horsetail you might see in different products:

  • A capsule: A standard dose has 10% to 15% silica in a capsule.
  • An herbal infusion: 2 to 3 teaspoons of dried horsetail taken three times per day
  • A tincture: The dosage should be chosen by your provider, but the ratio for making the tincture is 1-to-5.
  • A compress (for wounds or skin treatment): 10 grams of herb per 1 liter (33.8 ounces) of water each day

Working With Your Provider

There is not enough research on how much horsetail to use (the dose). With herbal supplements in general, there are several factors to consider. For example, your age and any health conditions that you have.

Your naturopath, pharmacist, physician, or another healthcare provider you are working with can help you figure out how much horsetail to use. You should also always read and follow the package inserts and labels that come with the products. 

Here are a few examples of how much horsetail might be used for different conditions. However, you need to talk to your provider about the dose that will be right for you.

  • Brittle nails: Products like creams that go on your skin may have horsetail in them. In studies, these products were applied every night for 29 days (or every other day for 14 days).
  • Diuretic: In one study, a dry extract of horsetail containing 0.026% total flavonoids was given as a 300 mg dose that a person took by mouth three times a day.
  • Wound healing: In one study, a 3% horsetail ointment was put on the episiotomy site of people who had recently given birth (postpartum) every 12 hours for 10 days.

Can You Take Too Much Horsetail?

There have been reports of toxicity from horsetail. However, some herbal experts still recommend it.

Storage

Like many prescription medications, herbal products need to be stored properly to make sure they keep working. All preparations of horsetail should be kept in a sealed dark container. They need to be protected from exposure to light.

Recap

Horsetail comes in different forms. Dried preparations can be made into a tea or added to other products. It can also go inside a capsule you can take like a pill. You can also get it in liquid forms.

Make sure you store horsetail products in a dark place that does not get a lot of light. This will help it last longer.

Summary

Horsetail is a plant that has been used for thousands of years. It's often found in products that are meant to help with hair growth or bone health. However, there is not enough research to prove that it is can treat medical conditions or is safe to use.

The FDA has not approved horsetail to treat any medical conditions. Herbal products like horsetail are also not regulated by the FDA.

A Word From Verywell

Always talk to your healthcare provider before taking an herbal supplement like horsetail. It's not OK to use horsetail if you take certain medications or have some health conditions.

There are different ways to use horsetail. It also comes in different amounts. If your provider thinks that it's fine for you to try horsetail, they will help you figure out which type to take and how much to use.

Frequently Asked Questions

  • Is it safe to eat horsetail?

    It depends. 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?

    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 includes 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?

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

  • Where does the name horsetail 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.

    Horsetail also goes by other names:

    • Asprêle
    • Bottle-brush
    • Coda cavallina
    • Cola de Caballo
    • Common horsetail
    • Equisetum
    • Field horsetail
    • Horse herb
    • Horsetail grass
    • Horsetail rush
    • Horse willow

    • Queue-de-Renard
    • Scouring rush
    • Shave grass
    • Spring horsetail

    Horsetail is not the same as the Callistemon plant, which has bristly red flowers that look like a bottle brush.


7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Bruno, G. Have a Good Hair Day. Huntington College of Health Sciences.

  3. Safiyeh S, Fathallah FB, Vahid N, Hossine N, Habib SS. Antidiabetic effect of Equisetum arvense L. (Equisetaceae) in streptozotocin-induced diabetes in male ratsPak J Biol Sci. 2007 May 15;10(10):1661-6.

  4. U.S. National Library of Medicine. EQUISETUM ARVENSE- equisetum arvense top pellet.

  5. Carneiro DM, Freire RC, Honório TC, et al. Randomized, Double-Blind Clinical Trial to Assess the Acute Diuretic Effect of Equisetum arvense (Field Horsetail) in Healthy Volunteers. Evid Based Complement Alternat Med. 2014;2014: doi:10.1155/2014/760683

  6. Penn State Hershey. Milton S. Hershey Medical Center. Health Information Library. Horsetail.

  7. James A. Duke, Ph.D. The Green Pharmacy Handbook. Emmaus, PA: Rodale Press, 1997:80.

Additional Reading

By Sherry Christiansen
Sherry Christiansen is a medical writer with a healthcare background. She has worked in the hospital setting and collaborated on Alzheimer's research.