Echinacea.

Echinacea is the name of a genus of native North American plants, commonly known as the purple coneflower. The most widely used herbal product in the United States is a liquid extract made from the root of Echinacea purpurea. Because the active component of the plant has not been identified, commercial echinacea products are not typically standardized to any particular component. The research literature on echinacea is difficult to evaluate because of the heterogeneity of the products used in various studies. The herb has been recommended as a prophylactic treatment for upper respiratory infection and is widely used for this indication. However, based on the current literature, it appears that prophylactic echinacea does not have a significant impact on the frequency, severity, or duration of upper respiratory infection. The data regarding treatment of upper respiratory infection appear to support a modest positive effect. No significant herb-drug interactions with echinacea have been reported; adverse effects reported generally have been uncommon and minor, including abdominal upset, nausea, and dizziness.