Randomized, controlled trials are designed to test specific hypotheses. While bias can be reduced, generalizability and interpretation are limited. In our trial, a specific echinacea preparation was tested against a specific control as a treatment for the common cold. The choice of echinacea was influenced by the literature and by popular practice. Several trials of Echinacea purpurea and E. angustifolia preparations had been positively reported (1, 2). Products containing either or both species were in wide use. We chose a capsulized whole plant preparation for its simplicity and ease of manufacture. We avoided a liquid preparation because the taste and tingling sensation of echinacea are notoriously difficult to disguise. We were intent on demonstrating intact blinding, since this had not previously been accomplished. This guided our choice of placebo. Because we used clear gelatin capsules containing the whole plant product, and because some of the herbal taste could leak from the capsules (and was available to participants who opened them), we needed a plant-based product that would be indistinguishable to participants and to research personnel. We settled on whole dried alfalfa because the color and consistency mimicked the echinacea product and no research had reported any effects of alfalfa on the severity or duration of the common cold. However, taste was still distinguishable, so technicians at Shaklee Technica experimented with adding various flavoring agents, eventually finding that a very small amount of thyme and peppermint successfully disguised echinacea's flavor.

We agree that these choices could affect results. Although a bit far-fetched, it is possible that tiny amounts of peppermint or thyme could block a positive effect of echinacea. It is also possible, although unlikely, that a few grams of alfalfa could be an effective treatment for the common cold. If so, the multimillion-dollar cold remedy industry should shudder, as a few grams of alfalfa costs only a few pennies. Perhaps an alfalfa trial will be carried out, and perhaps some benefit will be found. In the meantime, we stand by the results of our trial: The echinacea preparation we used provided no measurable benefit to college students experiencing cold symptoms. Perhaps it would have worked in an older sample. Perhaps a refined extract or liquid preparation would have worked. Perhaps dosing should occur within 12 hours rather than 36 hours of first symptoms. Our results cannot address these important questions, nor can our trial by itself negate the results of the several positively reported trials. More and better research is warranted.