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 is used for fluid retention (edema), kidney and bladder stones, urinary tract infections, the inability to control urination (incontinence), and general disturbances of the kidney and bladder. Horsetail is mostly consumed in the form of tea, which is made by steeping the dried herb in hot water.