Side effects are uncommon, but gastrointestinal irritation may occur. Isolated cases of renal and hepatic toxicity as well as anaphylactic reactions have been reported following intravenous administration, but these appear to be exceptional. Technically a pteridophyte more closely related to ferns than to flowering plants, the horsetail, a perennial, is actually weed-like, without flowers and rather dull, with scalelike leaves. Rushlike, it has hollow, jointed stems and uses spores, not seeds, to reproduce. Silica and silica acids are a large component of the stems.
Horsetails grow in moist, rich soils in all parts of the world except Australia.
Enthusiasts call this a valuable diuretic and astringent for treating various kidney and bladder ailments, ranging from kidney stones to cystic ulceration, and also recommend it as a rapid-acting remedy for dropsy. It is also called effective in treating tuberculosis. External application is supposed to stop the bleeding of wounds and promote rapid healing. Little scientific support exists of the healing properties of horsetail. It is a weak diuretic at best and should probably not be used, in favor of a safer and more effective drug.