Silver was used to treat nervous disorders in medieval times; tetanus and rheumatism in the 19th century; and colds and sexually transmitted diseases in the early part of the 20th century. Today, colloidal silver -- silver particles suspended in water or gel -- is marketed as a dietary supplement and antibiotics alternative.
Uses: Sometimes advertised as a cure-all capable of treating more than 600 conditions, from colds to cancer to AIDS, colloidal silver can indeed kill some bacteria and viruses in the laboratory. But its ability to fight infections in humans has not been proven.
Dose: Makers recommend 5 to 30 micrograms a day, taken orally. It's also available in sprays and douches.
Precautions: Silver can accumulate in the liver, brain and spinal cord as well as in the skin, causing argyria, in which the skin turns permanently blue or gray. High doses or long-term use may also cause kidney and nerve damage.
Research: Studies do not show colloidal silver to be safe or effective. The Food and Drug Administration says the supplement has no known benefits. It should not be confused with silver nitrate and silver sulfadiazine, prescription medicines used to treat burns and other skin conditions.