It's the average benefit among people who have the early stages of a cold - so, for some, it could have a stronger effect.
It's been tested on a group of 700 people aged from 12 to 80 years, all of whom had early symptoms of a cold. They were split into three groups: no treatment, Echinacea, or Echinacea or placebo. The latter group was not told which they had been given.
Overall, say researchers from the University of Wisconsin-Madison School of Medicine and Public Health, the supplement had a 10 per cent positive impact on the duration of a cold, which usually lasts around five days.
There were no side effects, and so Echinacea is doing more good than harm, they say.
(Source: Annals of Internal Medicine, 2010; 153: 769-777).