More than one-third of Americans use complementary and alternative medicine, according to a 2004 study by the National Center for Complementary and Alternative Medicine, a division of the National Institutes of Health. Of these, 19 percent used natural products such as herbs, botanicals and enzymes. Increasingly, market research and NIH studies show that consumers are turning to these products in the form of herbal teas or infusions in order to maintain good health, improve metabolism or increase resistance to the common cold or flu.