Licorice root contains a compound called glycyrrhizin that has been found to have pretty potent antiviral effects against serious diseases, such as HIV and SARS, and a number of studies have found that licorice-root extracts can fight off the flu, including strains of the avian flu virus. In Ayurvedic medicine, licorice root is used as an expectorant. A number of companies make licorice-root supplements and teas, but be sure they contain actual licorice—many products (licorice candy, for instance) don't contain the herb but anise seed instead. Also talk to a doctor or pharmacist if you’re taking any prescriptions, as licorice has been found to interfere with some medications.
Garlic boosts the health of your immune system, and a number of studies have found that animals given regular doses of garlic are better able to ward off viruses like the flu and various strains of rhinovirus, the kind responsible for the common cold. In one study from 2001, volunteers who took a daily garlic supplement were less likely to get colds than volunteers taking a placebo, and even when the garlic takers did get sick, they recovered more quickly. For the sake of people who have to talk to you, garlic supplements are probably the kindest way to go. But you can also get the same benefits by chewing on a clove of garlic once a day for prevention, or twice a day to get over a cold or flu. Mince a clove of garlic into some honey if the flavor is too overpowering. It’s not clear whether adding more garlic to your cooking affords the same protection, but why not? It'll only taste great.
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.
Another botanical that helps you cope with cold and flu symptoms is elder, also known as black elder. The extract of elderberries has been tested repeatedly and found to shorten the duration of symptoms by as much as 4 days, and the extract has been found effective at fighting up to 10 strains of flu virus. Nearly all of the scientific studies conducted on elderberry have used a commercial product called Sambucol, which is available as a liquid supplement from a number of different companies.