Herbal medicines have now reached widespread use in the United States. Of the many popular herbal remedies available, one that has received a great deal of attention is echinacea. Several completely different preparations are referred to as echinacea. Reasons for the differences include: the use of three different species of echinacea (Echinacea purpurea, Echinacea pallida and Echinacea angustifolia); the use of different plant parts; different methods of extracting the active ingredients; and the addition of other plant extracts. While there have been many claims of positive effects from echinacea, the most notable is its potential to prevent upper respiratory tract infections. Melchart and associates performed a double-blind, placebo-controlled, randomized trial to determine whether extracts from the roots of E. angustifolia or E. purpurea are effective in the prevention of upper respiratory tract infections in healthy volunteers.

The study included 302 volunteers who did not have an acute illness at the time of enrollment. They came from four military institutions and one industrial plant in Germany. The participants were given an ethanolic extract from the roots of either E. purpurea or E. angustifolia, or placebo, taken orally for 12 weeks. The observed time until first upper respiratory tract infection was the main outcome measure, as well as the number of participants with at least one infection, global assessment and adverse effects.

The authors found no significant differences among the three groups in regard to onset of first upper respiratory tract infection. The time until occurrence of the first upper respiratory tract infection was 66 days in the E. angustifolia group, 69 days in the E. purpurea group and 65 days in the placebo group. There were also no significant differences among the groups in the number, severity or duration of upper respiratory tract infections or in perceived quality of life. Although more subjects in the treatment groups than in the placebo group believed that they benefited from taking the medication, the E. angustifolia group had more adverse effects, mainly minor gastrointestinal symptoms, headache and dizziness.

The authors conclude that the results of this study do not support the widespread belief that echinacea prevents upper respiratory tract infections. However, the findings point to the need to perform future randomized control trials with a larger number of subjects, over a longer study period and with efforts to reduce the chance that subjects can distinguish active drug from placebo.