Last summer, an analysis in the journal Lancet Infectious Disease showed that in well-designed studies, Echinacea purpurea shortened colds by an average of 1.4 days and reduced the odds of getting a cold by 58%. (Most studies administered around 900 milligrams or 8 to10 milliliters.)
The same report looked independently at five rigorously designed studies on Echinaguard and Echinacin, two proprietary blends of Echinacea purpurea juice, and found that they reduced the risk of getting a cold by 56%.
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Dr. Robert Bonakdar, a physician with the Scripps Center for Integrative Medicine in La Jolla, pointed out that taking the right echinacea species is critical. A Cochrane review concluded that only Echinacea purpurea products showed any promise in treating colds, and only when they contained the aboveground parts of the plant -- not the root. Unfortunately, other formulations abound. Echinacea products can contain the roots, leaves or flowers of any of three species of the plant (purpurea, pallida or angustifolia), in dried, powdered or extracted form.
They may not even contain the plant. Researchers at University of Colorado Health Sciences Center published a paper in the Archives of Internal Medicine in 2003 showing that 10% of the echinacea products on store shelves in Denver contained no measurable echinacea at all.
The Cochrane reviewers stressed that echinacea showed promise only when taken early in a cold. Bonakdar concurred. "With any product, if you're not using it consistently, it's not going to have a benefit," he said.