context: Echinacea has been long used to fight colds and infections, and many experts recommend its use. It is one of the most popular supplements in the U. S. Many people take echinacea in the hopes that it will boost immunity. Studies have had mixed results. So far, evidence suggests that echinacea may prevent the common cold. It also might help as a treatment. Some studies, many of them small, have found that taking echinacea may reduce the length of a cold and the severity of its symptoms. However, two large clinical trials found no benefits at all. It's important to note that there are different species of echinacea, such as Echinacea purpurea, Echinacea pallida, and Echinacea angustifolia. Some of the conflicting findings may result from researchers testing different varieties. The strongest evidence for echinacea as a cold treatment comes from studies of Echinacea purpurea. Studies of Echinacea angustifolia and any echinacea root have had weaker results. Echinacea may not work as well in children and young adults as it does in older adults. When taken along with an antifungal cream, oral echinacea may help prevent recurrent vaginal yeast infections. While some studies suggest that echinacea may slightly reduce flu symptoms, the evidence isn't clear. Echinacea does not seem to help prevent or treat herpes. The effect of echinacea on other conditions is not known. There is no standard dose of echinacea. It depends in part on the form you use. For example, the usual dose range for pressed juice is 6-9 milliliters daily, and the usual dose range for tinctures (usually a solution of alcohol and herbal extract) is 0.75-1.5 milliliters daily. Standardized extracts have other specific doses. Some people use echinacea tea, 6-8 ounces, four times daily. Echinacea appears to be most effective when started as soon as symptoms are noticed, taken many times a day, and used for seven to 10 days. It is possible that liquid forms of echinacea (such as alcohol or glycerin-based tinctures) might work better than capsules -- as they're being swallowed, these liquids could have an antiviral effect on the mucous membranes of the back of the throat. There are no natural food sources of echinacea. Side effects. When taken at normal doses, echinacea causes few side effects. Some people have reported symptoms like upset stomach, headache, sore throat, drowsiness, and rash. Risks. Although rarely, echinacea can cause allergic reactions. Some can be serious. If you have asthma or an allergy to certain plants and flowers -- like ragweed, chrysanthemums, marigolds, or daisies -- be cautious when using echinacea. Taking echinacea by injection is dangerous. Check with a doctor before using echinacea if you have an autoimmune disease like lupus, rheumatoid arthritis, MS, or if you have HIV. Interactions. If you take any drugs regularly -- particularly drugs that suppress the immune system -- talk to your doctor before you start using echinacea supplements. There is also some concern that echinacea could cause liver problems in people who are also taking certain painkillers (like Tylenol), antidepressants, blood thinners, sedatives, and other drugs. Given the lack of evidence, children and pregnant or breastfeeding women should not take echinacea unless their doctors have approved it.