In the United States, astragalus has been presented as an immune stimulant useful for treating colds and flus. Many people have come to believe that they should take astragalus, like echinacea, at the first sign of a cold.

The belief that astragalus can strengthen immunity has a partial basis in traditional Chinese medicine. The expression noted above, "stabilize the exterior," means helping to create a "defensive shield" against infection. However, according to tradition, astragalus formulas should not be taken during the early stage of infections. To do so is said to resemble "locking the chicken-coop with the fox inside," causing the infection to be "driven deeper." Rather, astragalus is supposedly appropriate only for use while you're healthy, for the purpose of preventing future illnesses.

Although Chinese herbal tradition suggests that astragalus should generally be used in combination with other herbs, modern Chinese investigators have found various intriguing effects when astragalus is taken by itself. Extracts of astragalus have been found to stimulate parts of the immune system in mice and humans, and to increase the survival time of mice infected with various diseases.^2,3 Astragalus has also been shown to enhance diuresis (urine output) by encouraging the kidneys to release more sodium into the urine.¹² Other highly preliminary research suggests that astragalus might be useful in treating atherosclerosis, hyperthyroidism, hypertension, insomnia, diabetes, chronic active hepatitis, genital herpes, AIDS, and increase the efficacy and/or reduce the side effects of cancer chemotherapy.^{4-9, 11} However, none of these possibilities can be regarded as proven.

Astragalus appears to be relatively nontoxic. High one-time doses, as well as long-term administration, have not caused significant harmful effects.¹⁰ Side effects are rare and generally limited to the usual mild gastrointestinal distress or allergic reactions. However, some Chinese herb manuals suggest that astragalus at 15 g or lower per day can raise blood pressure, while doses above 30 g may lower blood pressure.

As mentioned above, traditional Chinese medicine warns against using astragalus in cases of acute infections. Other traditional contraindications include "deficient yin patterns with heat signs" and "exterior excess heat patterns." Because understanding what these mean would require an extensive education in traditional Chinese herbal medicine, we recommend using astragalus only under the supervision of a qualified Chinese herbalist.

Safety in young children, pregnant or nursing women, or those with severe liver or kidney disease has not been established.