A recent report showed that 300 mg of Echinacea appears to have little to no effect on cold symptoms. Researchers administered Echinacea within 24 hours of first cold symptoms and found that patients reported equally severe symptoms in the Echinacea group and in the placebo group. Both groups experienced the same recovery time.
Last year, a similar study showed that children who took Echinacea as soon as they developed a cold had no difference in the severity or the duration of the cold, compared with children who took a placebo. Whereas some of the studies may show Echinacea to be effective, Steven H. Yale, MD, of the Marshfield Clinic in Wisconsin attributes this difference to the type of Echinacea plant used and the amount administered. He strenuously warns against using Echinacea because of the unknown side effects or drug interactions.