Does Echinacea Extract Prevent or Ameliorate Respiratory Infections?
Echinacea is purported to be an immunostimulating agent capable of preventing or relieving a variety of conditions, such as colds and other respiratory infections, chronic arthritis and chronic fatigue syndrome. However, clinical efficacy has not been proved in randomized controlled trials. Grimm and Müller conducted a double-blind, placebo-controlled study of the effects of a fluid extract of Echinacea purpurea to determine whether it reduces the incidence and severity of the common cold. The 108 subjects in the eight-week study had a history of at least three respiratory infections or colds during the preceding year. They were randomly assigned to receive 4 mL of the echinacea extract or placebo twice daily. Follow-up visits were four and eight weeks after beginning the study. In addition, the subjects were instructed to seek follow-up if they noted the onset of cold symptoms. If a cold occurred, patients were evaluated every two to three days, and the severity of the cold was rated
