There isn’t much evidence that echinacea will do anything for you once you get a cold, other than possibly shorten the duration of your symptoms. But there is some evidence that it could prevent colds and flus if taken in conjunction with garlic supplements, according to an article in the Journal of the National Medical Association. The problem with most echinacea products on the market is that they don’t tell you how much of the herb is in the product. Forgo teas and instead take a supplement containing 1000 milligrams three times a day. One note: People who are allergic to ragweed or to pollen may be allergic to echinacea, as well.