Cordyceps sinensis is a type of fungus that has been used for thousands of years. Cordyceps is also known as Chinese catepillar fungus, because it is a parasite that grows on the Tibetan caterpillar until the caterpillar dies, at which point it sprouts a mushroom. (Don't worry, most cordyceps produced commercially in Western countries is actually grown on plant sources, such as soybeans.) The Chinese have long used cordyceps to promote overall good health, and modern research indicates that cordyceps does indeed support liver, kidney, heart, and immune system function. It also appears to act as an antioxidant in the body, protecting it from free radical damage.