For reasons that escape scientific explanation, this daisylike flower seems to charge up the immune system. Many studies show that echinacea lessens cold symptoms and speeds recovery by a day or two. A 2007 review of over 700 studies found that it has substantial effect on preventing colds—it can reduce your risk of catching one by 58%—and it might shorten the duration of an existing one. "As soon as I feel a cold coming on, I take it. My colds are mild and brief," says James Duke, PhD, retired chief of the U.S. Department of Agriculture's Medicinal Plant Laboratory in Beltsville, Md., and the author of many books about herbal medicine, including The Green Pharmacy and Dr. Duke's Essential Herbs.
Promising, yes, although even the researchers admit more-standardized trials are needed to confirm this supplement's effectiveness. There's still no consensus on how much echinacea can shorten a cold's duration, though. And not all scientists are in agreement. There are 200 types of viruses that can cause colds, and research hasn't shown which strains echinacea works against. Also, what works well for you is not necessarily effective for your kids: A 2003 study at the University of Washington showed that echinacea does not help relieve cold symptoms in children.
Dosage: Take the herb in tea or capsule form several times a day from the moment cold symptoms appear until you feel better. Doses vary depending on the form, so follow the label instructions.
Caveats: To lower the risks of side effects, take the pills. Liquid products may upset your stomach or cause temporary, harmless numbing or tingling of your tongue.