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An herb used extensively to prevent and treat the common cold. It is one of the most widely used herbal supplements in the United States, with annual sales surpassing $300 million. Of the nine known species of echinacea, the three that are most often used medicinally are E. purpurea, E. angustifolia, and E. pallida. The flowers, leaves, stems, seeds, and roots of these plants are used fresh or dried to make teas, squeezed juices, and extracts to be taken by mouth, as well as topical preparations for wounds and skin conditions. Echinacea is believed by some to fight off the common cold by stimulating the immune system.

To date, studies of echinacea’s potential to prevent or treat the common cold have yielded inconsistent results. Isolated studies have suggested some benefits, but many have not, and at least some of the studies showing benefits had design flaws. Three large studies funded by the National Center for Complementary and Alternative Medicine, a branch of the National Institutes of Health, have failed to show any benefit from echinacea in preventing or treating the common cold.

In one study, published in the journal Annals of Internal Medicine in 2002, a capsule filled with E. purpurea and E. angustifolia failed to show any benefit in 142 college students with colds. In a second study, published in The Journal of the American Medical Association in 2003, E. purpurea failed to ease cold symptoms in 407 children ages 2–11. In a third study, published in The New England Journal of Medicine in 2005, E. angustifolia failed to have any effect on 399 healthy volunteers’ risk of developing colds or the severity or duration of cold symptoms in those who developed colds. Furthermore, a recent systematic review of published studies found no evidence that echinacea was effective in treating children with colds. Echinacea may help alleviate symptoms of a cold, but there is not yet solid proof that it works.

Taken by mouth, echinacea generally does not cause side effects. However, allergic reactions are possible and may be more likely in people who are allergic to plants in the daisy family, which includes ragweed, chrysanthemums, marigolds, and daisies. Also, because of its possible effects on the immune system, people who have an autoimmune condition or who are taking immunosuppressant drugs are often advised not to take echinacea. As with any dietary supplement, it is a good idea to speak to your health-care team before using echinacea.

Originally Published November 23, 2009

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