Astragalus, or huang qi, is to Chinese medicine what echinacea is to the North American materia medica. It is the Chinese herbal practitioner's number-one herb to boost Qi (pronounced "chee" and translated as "energy flow" or "breath"), in people who are frequently sidelined by colds and the flu. In Chinese medicine, when someone gets sick we say that their "protective Qi" is deficient, and astragalus acts to stabilize this protective Qi running along the surface of the body. How do you know if you have a weak immune system? Exhaustion, food allergies and depression can all leave the body vulnerable to infection, leading to persistent colds or flu, frequent skin infections, and/or chronic fatigue — all key symptoms.
Astragalus also helps a number of other problems, including spontaneous sweating, low appetite, and recovery from long-term illness, and can improve immune function in people with cancer and HIV.
Note: One should not use astragalus during an acute illness — only as a preventative. For this reason it's best to take it under the care of a licensed acupuncturist, who can make a proper diagnosis and treatment plan.