Healers in centuries past considered the plant valuable for controlling bleeding from lung lesions caused by tuberculosis. Interestingly, studies in animals indicate that it also helps to stanch bleeding when applied directly to a wound.
Today, the most notable use for horsetail is as a mild diuretic (''water pill'') to increase urination and lessen swelling, and as a remedy for various bladder and kidney problems (including kidney stones and bladder infections). Scientists have even identified the compounds in horsetail that promote fluid loss (equisetonin and flavone glycosides). Anti-inflammatory qualities have spurred its use for inflammatory gastrointestinal conditions such as Crohn's disease. Claims that horsetail can promote weight loss (beyond simple water loss) are unfounded, however.
As a rich and natural source of easy-to-absorb silica, horsetail is likely to be effective in strengthening nails, hair, and teeth; the body requires silica to keep such connective tissue (as well as joint cartilage) healthy and strong. In fact, it's the presence of silica that accounts for the herb's use to prevent osteoporosis ("brittle bones"), to treat bursitis and tendonitis, and to enrich "natural" formulas for baldness.
Liquid extracts, capsules (including freeze-dried whole herbs), tablets, and dried horsetail for loose and prepared tea are widely available. To prepare horsetail tea, steep 1 tablespoon of dried herb in 1 cup (8 ounces) of hot (not boiling) water; adding a little sugar reportedly releases more silica from the leaves. To use the liquid extract, add 1/2 teaspoon to a glass of water; drink three times a day. To use the freeze-dried whole herb capsule (it's quite potent in this form), take one capsule three times daily.
