The purple coneflower Echinacea purpura, and its close relatives, E. angustifolia and E. pallida, are the source of the herb Echinacea, which is widely popular as a non-specific immune stimulant. These perennials are native to the prairies of North America and are now widely grown garden ornamentals. The root and aerial parts of the plant are the portions used, and the preparation’s potency can be verified by the transient tingling sensa-tion produced when it is tasted. Echinacea contains alkamides, caffeic acid esters (echinacoside, cichoric acid, caftaric acid), polysaccharides (heteroxylan), and an essential oil. Some echinacea products are standard-ized for their echinacoside content. In the past, adulter-ation with American feverfew (Parthenium integri-folium) was common. Echinacea is now sold either by itself or in combination with golden seal or zinc for the treatment of colds and influenza.
Echinacea extracts appear to stimulate the number and activity of immune cells (i.e., increasing physiological levels of tumor necrosis factor and other cytokines)and to increase leukocyte mobility and phagocytosis. The ex-tracts also have antiviral and antiinflammatory proper-ties and inhibit bacterial hyaluronidase.
There are numerous studies on echinacea in the litera-ture, many of which indicate either an in vitro immune stimulation or a significant clinical reduction in the severity and duration of upper respiratory viral symp-toms, especially when taken early in the onset of symp-toms. Despite several of these meta-analyses concluding that echinacea is an effective immunomodulator of acute infection, there is still controversy as to the extent of its clinical effectiveness. A number of trials now clearly indicate that echinacea is unlikely to be effective in the prevention of colds, even if it may slightly shorten their course.
In vitro antiinflammatory effects have been docu-mented, and the herb has a long history of being used externally for wound healing, psoriasis, and the reduc-tion of skin irritation. Although there are a few small positive studies, the available evidence is not yet con-clusive in regard to clinical use.
Echinacea appears to be a very safe herb, producing only minor gastrointestinal (GI) side effects and an occasional allergic reaction, usually in atopic patients already sensi-tized to other members of the Compositae plant family. Anaphylaxis has occurred rarely. Use in HIV is discour-aged because of the concern that long-term therapy may eventually suppress the immune system.
It is recommended that echinacea not be taken by anyone for more than 8 continuous weeks, and most clinical use is under 2 weeks’ duration. Echinacea has not yet been shown to be safe in pregnant or breast-feeding women and small children. No specific herb–drug interactions are reported, but for theoretical reasons those taking immunosuppressant drugs should avoid echinacea.
Usually echinacea is given as a capsule, but it is also available as an alcohol-based tincture. The use of echi-nacea tea is less desirable, since not all of the compo-nents are water soluble. Unfortunately, there are signif-icant differences in the potency of commercially available supplies, depending on the plant species and the part and age of the plant used.
While it is still controversial, there is some evidence that echinacea stimulates the immune system and may miti-gate some of the symptoms of viral infection. However, it does not appear to be helpful in preventing viral in-fections, and long-term use should be avoided.
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