Horsetail, or Equisetum arvense, is an herb that has historically been used as a diuretic to make you urinate more frequently. Diuretics affect the kidneys, increasing the amount of water and salt released into the urine. For people with kidney problems, getting rid of unwanted fluid and salt can be an important part of treatment. Diuretics may also be helpful to people with edema, a condition in which the body holds onto fluid.

Horsetail is a descendant of a much larger plant that grew 3 hundred million years ago. Today, it grows in Europe, North America, and Canada. Its tube-like stems and scale-like leaves make it look like a cross between a bamboo plant and a fern. Horsetail remedies are made using the leaves and stems. You can purchase horsetail as a liquid extract or in dried form in a tea or capsule.

Horsetail is believed to contain chemicals that increase the amount of urine the body produces. Researchers aren’t yet sure exactly how or why the herb may work. There is little solid evidence to prove that it is effective. A recent study compared horsetail to a common diuretic, hydrochlorothiazide, and found the herb to be as effective as the medication without causing excessive electrolyte loss. However, the study was very small, so the results are not considered conclusive.

Horsetail has been used medicinally since as long ago as ancient Greece. Beyond its potential benefits as a diuretic, horsetail has also been used for skin and nail care, wound healing, osteoporosis, and bone repair. Some researchers hypothesize that the plant’s possible health benefits may be due to a mineral called silica. The mineral helps your body store calcium needed to heal bones, and to build strong fingernails and hair.

Silica gives horsetail a coarse texture that also makes it useful for cleaning. For this reason, the herb is used in some beauty products such as facial cleansers and shampoos.

You can buy horsetail supplements in pill form or as a tea at most health food stores. The tea is made by boiling a teaspoon of dried horsetail with water, and adding sugar. If you live in an area where horsetail grows, it’s also possible to cut the herb and dry it yourself.

Like most herbal supplements, horsetail is not approved by the U.S. Food and Drug Administration. If the herb has a diuretic effect, it might cause your body to flush out essential nutrients, such as potassium. Horsetail also has an enzyme that destroys thiamine, or vitamin B-1. If taken for a long time, it could raise your risk of thiamine deficiency.

Horsetail can also affect the way your body processes lithium, which could cause dangerous side effects if you use it as medication. People with diabetes should be cautious when it comes to horsetail, since the herb may drastically lower blood sugar.

Since there have been few studies on horsetail, there is no standardized dosage. Supplements generally have recommended doses on the label. Check with your doctor or pharmacist before you start using horsetail.