(See also Overview of Medicinal Herbs and Nutraceuticals.)
Zinc, a mineral, is required in small quantities for many metabolic processes. Dietary sources include oysters, beef, and fortified cereals.
People most often take zinc in the form of lozenges to reduce the duration of cold symptoms. Scientific studies are inconsistent, but if zinc has an effect, it probably is small and occurs only when it is taken very soon after cold symptoms develop.
Zinc is generally safe, but toxicity can develop if high doses are taken. The common side effects of zinc lozenges include nausea, vomiting, diarrhea, mouth irritation, mouth sores, and bad taste. Because zinc is a trace metal and can remove other necessary metals from the body, zinc lozenges should not be taken for more than 14 days. Zinc sprays may cause nose and throat irritation.