Echinacea purpurea is also sometimes called the purple coneflower. These are tall weeds with purple flowers that grow in the prairie regions of the USA. The plants have edible roots, leaves and seeds and were used by Native Americans mainly for medicinal purposes. Both the roots and above ground parts of the plant are used in supplements and they contain a number of phenols which are derivatives of caffeic acid (e.g. cichoric acid and caftaric acid) which are in the category of phenols listed earlier as hydroxycinnamates. As with many herbal extracts, it is not known which (if any) of the many secondary metabolites are the ‘active ingredients’ although the phenol content is used to assess the quality of Echinacea preparations.
The main claim for Echinacea is that it is an immune stimulant and that it may be beneficial in preventing and/or treating upper respiratory tract infections (colds and flu). There have been numerous trials of the benefits of Echinacea for treating and preventing colds and flu: these trials have used a variety of different preparations and many have had major methodological flaws. Melchart et al. (2000) conducted a systematic Cochrane review of Echinacea and identified eight prevention trials and eight treatment trials. Their conclusions were that some Echinacea preparations may be better than placebos, although the data was not of sufficient homogeneity or quality to perform a quantitative meta-analysis. The authors concluded that the evidence then available was not sufficient to recommend Echinacea for the treatment or prevention of colds.
Since 2000 there have been several other trials of Echinacea, most of which have found it to be ineffective in preventing colds or in reducing the duration and severity of symptoms in adults or in children. One trial reported that subjects given Echinacea at the onset of an upper respiratory tract infection had significantly lower score on a subjective ‘severity of symptoms’ scale than those receiving a placebo. The latter authors used a formulation made from freshly harvested Echinacea purpurea plants and suggest that perhaps the negative results obtained in many other trials may be attributable to the low level of active ingredients in the Echinacea preparations used. Even in this one recent, positive study, however, the apparent benefits of the Echinacea were modest. There seem to be no grounds for the routine long-term use of Echinacea as a dietary supplement; the evidence supporting its use as a short-term medication at the onset of an upper respiratory tract infection is also very weak. Echinacea is available in tablet or liquid form and special preparations for children are also sold. It is difficult to specify a dose because of the variability in the content of the commercial preparations. One major UK supplier produces tablets which contain concentrated extracts of the plant juice which they say is the equivalent of just over 3 g of the fresh herb and is standardised to contain 3% of cichoric acid, one of the phenols that may be bioactive.