Four prescription antiviral drugs are approved for treating the flu.

Amantadine (Symmetrel) and rimantadine (Flumadine) reached the market first. Zanamivir (Relenza) and oseltamivir (Tamiflu) became available last year. If you start taking one of these drugs within two days of your first flu symptoms, the drug may shave a day off your illness.

But federal health officials warn against using the drugs to prevent the flu. "These drugs are not a substitute for influenza vaccine and should not be used as such," the CDC warned in a statement issued in June.

Amantadine and rimantadine have been associated with adverse reactions involving the central nervous system. And Relenza is linked with severe side effects, even death, in people with asthma, emphysema and other airway diseases.

If you're at high risk for flu complications, or have to be back at work in three days, it might make sense to see a doctor about an antiviral drug -- that is if you get the flu. But the potential benefits of taking one of the drugs to prevent the flu probably don't outweigh the risks, especially when an effective flu vaccine is available.

Echinacea to Zinc

There are almost as many "natural" preventives for colds and flu as there are cold-and-flu viruses. Unfortunately, only a few of the treatments have been studied and the evidence for these remains mixed.

"Herbals and dietary supplements offer significant potential, but consumers beware," says Eric Gershwin, M.D., an allergist and director of the University of California at Davis Center for Complementary and Alternative Medicine Research in Asthma, Allergy and Immunology. "Most products on the market are not tested, have no standardization, have little or no scientific basis and may even be harmful. This may change with good research to separate the good products from the junk."

Gershwin recently reported, for example, that two ginseng species showed significant effects on volunteers' white blood cells. American ginseng stimulated the cells to divide and grow, suggesting a positive effect on the immune system. Siberian ginseng also stimulated immune cell growth -- but only at moderate doses. At a higher dose, the Siberian ginseng was toxic to the cells. Panax ginseng, meanwhile, had no effect.

Echinacea, widely touted as a natural way to enhance immunity, is prescribed in Germany for colds and flu. But scientific studies so far have yielded conflicting results about the plant's efficacy. The UC Berkeley Wellness Letter warns people not to try echinacea if they're allergic to daisies or have lupus, rheumatoid arthritis, tuberculosis, multiple sclerosis or AIDS. The newsletter also warns against use by children and pregnant and nursing women.

For zinc lozenges, the research again is divided. While about half of the studies show the lozenges can cut the duration of a cold by up to half, the others show no effect. A recent study in the Journal of the American Medical Association found that kids who used zinc lozenges took just as long to get over their colds as those who took a placebo -- but complained more of bad taste; nausea; mouth, tongue and throat irritation; and diarrhea.

If you're going to use zinc lozenges, use them as directed to treat a cold.

Taking them on a regular basis to prevent colds could be risky. The American Medical Association warns that large doses of zinc in zinc supplements can interfere with the body's absorption of copper, iron and other minerals essential to immune function. Megadoses of zinc also can impair formation of red blood cells, depress the immune system and reduce levels of "good" HDL cholesterol.

What about vitamin C? The UC Berkeley Wellness Letter recently revisited the vitamin C question, and reaffirmed its recommendation that people eat a diet rich in vitamin C and take a daily vitamin C supplement of 250 to 500 milligrams. But the editors emphasized their recommendation is based on evidence that vitamin C helps to prevent heart disease and some cancers -- not colds.

"Nearly everyone agrees now that vitamin C can't prevent a cold," the newsletter reported.

(c) 2000, Claudia Morain. Distributed by Los Angeles Times Syndicate