Echinacea and the common cold

The herbal remedy ingredient echinacea can reduce the risk of getting a common cold by more than half and reduce the duration of colds by 1.4 days, reported The Independent . Researchers “found that echinacea remedies can reduce the time that a person, once infected, is affected by a cold virus,” it said. The newspaper went on to say, however, that the researchers “stopped short of recommending the prescription of echinacea” until further research could be carried out.Echinacea is the name of a group of plants, most of which have pinkish-purple flowers. The root, seeds and other parts are used in herbal remedies.

Where did the story come from?

This systematic review of randomised clinical trials involving echinacea and the common cold was conducted by Craig Coleman and colleagues at the University of Connecticut and was published in the peer reviewed medical journal the Lancet Infectious Diseases .

What kind of scientific study was this?

Mathematical methods were used to combine the results of multiple studies comparing products containing echinacea with control (no echinacea) and the effect they have on the duration of colds and on the number of new colds people get (incidence). Echinacea was given either before onset of a cold, at the first sign of a cold or during an active cold. All studies used different types of echinacea, different doses of echinacea and/or different preparations of product. 

What were the results of the study?

The review found that overall, the use of echinacea products, before a cold, just as a cold was starting or for the duration of an active cold reduced the number of cold episodes from 65% in the control group to 45%. People who took echinacea products were ill for an average of 1.4 days less than those who took nothing.

What interpretations did the researchers draw from these results?

The researchers interpreted the results to mean "that echinacea decreased the odds of developing the common cold by 58%” and reduced “the duration of a cold by 1.4 days”.

What does the NHS Knowledge Service make of this study?

We can’t draw definitive conclusions about the effects of echinacea on the common cold due to weaknesses with the evidence looked at in this review:

  • Echinacea only reduced the duration of the common cold when it was given with other supplements, and not when it was taken on its own, suggesting that other ingredients may also be having an effect.
  • The studies included in the review were of varying quality and gave varying results from one another. This variation could be due to other study factors, some of which the authors tried to investigate. Combining widely variable study results to get a single measure of effect has problems. The variation may be explained by the inclusion of unblinded (definition) studies (those where the investigator or the participant or both knew what treatment was being given). Different echinacea preparations were also used in most studies and it is unclear whether these are commercially available preparations. As the authors acknowledge, previous studies have shown there to be concerns with the ingredients and quality of commercially available preparations. 
  • The results of this study could be misinterpreted. The odds reduction should not be interpreted as a reduction in risk. The study actually showed that compared with people who didn't take echinacea, those who did were about 30% less likely to get a cold (not 58%).

Overall, more robust research is needed before the effects of echinacea on prevention or treatment of common colds can be understood.

NHS Attribution