Horsetail is principally used for its content of water-soluble, colloidal silica. It is therefore primarily a treatment for connective tissue problems and internal bleeding, but also has diuretic properties and may help to remove excess lead from the body. The plant should be boiled in water for three hours with a little sugar to extract the silica.
One of the most important uses of horsetail is as a urinary astringent, helping to reduce irritation of the bladder sphincter and therefore combating frequent urination. This astringent effect is thought to be particularly helpful against the problems associated with prostate enlargement in men.