Does echinacea really work against the common cold?

Products sold as 'echinacea' differ enormously from one another: the plant species used, the plant part (root or above-ground portion) and the method of preparation vary widely. This makes summarising studies difficult from the outset, because they are not always investigating the same product.

For prevention, that is, stopping a cold before it starts, the research shows no convincing effect. In a large Cochrane analysis of twelve comparisons, not a single one was statistically significant. There is a small, non-significant trend of 10 to 20% fewer colds, but whether this translates into any real-world benefit is unclear. In addition, a review aimed at general practitioners did not include echinacea on the list of remedies with proven efficacy: painkillers, zinc, nasal drops and ipratropium are the ones that qualify.

For treatment, that is, shortening a cold once you are already ill, the results are contradictory. One meta-analysis calculated an average reduction of 1.4 days, but a more rigorous Cochrane analysis found no consistent significant effect. Only for Echinacea purpurea derived from the above-ground parts is there some indication that starting early may offer a degree of benefit: several trials with this type of product did see an effect, although that was not the case in all studies.

Safety is not a major cause for concern. The number of people who dropped out due to side effects did not differ appreciably from the placebo group. In prevention studies, a small trend of slightly more dropouts in the echinacea group was noted, but this was not statistically significant.