(See also Overview of Medicinal Herbs and Nutraceuticals.)
Echinacea is a perennial herb that contains echinacoside and several other active substances. Various parts of the plant are used medicinally.
People take echinacea mostly to help prevent or treat viral infections in the upper respiratory tract, such as the common cold. Some people apply echinacea as a cream or ointment to treat skin disorders and promote healing of wounds.
Many studies have evaluated the effects of echinacea on colds, but none is considered conclusive. One problem is that there are many different preparations of echinacea, and there is no standard dosage. However, several of the better-designed studies show no benefit from echinacea in cold prevention or treatment.
Echinacea may interact with drugs that can cause liver damage, thereby increasing the risk of liver damage. Echinacea may negate the effects of immunosuppressants, which are used, for example, to prevent rejection of organ transplants. People who have type 1 diabetes, autoimmune diseases (such as rheumatoid arthritis and multiple sclerosis), or an impaired immune system (for example, by AIDS or tuberculosis) should consult their doctor before they take echinacea.