Studies on the effectiveness of echinacea at preventing or shortening colds is mixed. Some studies show no benefit. Others show a 10 percent to 30 percent reduction in severity and duration when taken for seven to 10 days at the onset of the cold.

Some people swear by Airborne, a popular herbal cold remedy that's sold over-the-counter in many drugstores. - "Cold remedies: What probably doesn't hurt"

Study results are mixed on whether echinacea effectively treats colds or flu. For example, two NCCAM-funded studies did not find a benefit from echinacea, either as Echinacea purpurea fresh-pressed juice for treating colds in children, or as an unrefined mixture of Echinacea angustifolia root and Echinacea purpurea root and herb in adults.

However, other studies have shown that echinacea may be beneficial in treating upper respiratory infections. Most studies to date indicate that echinacea does not appear to prevent colds or other infections. - "Echinacea"