This herbal remedy, prepared from the purple coneflower, is still up for great debate in the medical community. (File under: More research needed.) But here's what you need to know to cut through all the existing crap: While there's no evidence taking echinacea will prevent a cold, it could possibly reduce a cold's duration, according to one 2010 study in the Annals of Internal Medicine. So if you're a believer, keep some on hand and take it as the first signs of that itchy throat and sniffly nose surface. The recommended dose for adults is two capsules or one teaspoon of the liquid version four times a day.