Echinacea is not a new treatment; more than 400 years ago, Native Americans were using it to treat infections and for other medicinal needs. In fact, the flower was officially listed in the U.S. Pharmacopeia and National Formulary (USP-NF) in the first half of the 20th century, but its popularity and usage declined with the introduction of antibiotics.
Today echinacea is having a revival of sorts, and the herbal supplement is commonly taken to prevent the onset of or reduce the symptoms of the common cold and other upper respiratory tract infections. While some swear by the healing power of echinacea, at least if started as the first symptoms appear, scientists can't agree -- but, neither can they disagree. Echinacea may help the body decrease inflammation by perking up your immune system, and if that's the case it may also ease cold symptoms. Although it may not work that way at all. Clear as mud?
A 2007 study found that echinacea supplements did reduce the duration of the common cold by as much as (on average) 1.4 days. If taken before the cold takes hold, echinacea may reduce the risk of catching a cold in the first place by as much as 58 percent [source: Paddock]. However, in 2010 a new study concluded that taking echinacea didn't improve the duration or symptoms of a cold any better than a placebo could; in fact, the most optimistic -- yet statistically insignificant -- outcome suggested it may reduce the length of a cold by about seven hours [source: Paddock]. So the jury's still out.
In addition to treating colds, some people also use echinacea to treat problems including typhoid, malaria, and genital herpes; there's no clinical evidence echinacea would be beneficial treating any such things.