The root of the legume Astragalus membranaceus (milk vetch or yellow vetch) is one of the most common tonic herbs in Chinese herbal medicine. Astragalus is a very large genus; in North America there are nearly 400 Astragalus species, located mainly in the western United States. Some of these, such as the infamous "loco-weed," are poisonous to livestock due to their high selenium content. Other species of Astragalus, like membranaceus, are nontoxic. The common food and cosmetic ingredient, gum tragacanth, is obtained from several nontoxic Astragalus species.38 The medicinal use of Astragalus membranaceus was discussed in the 2,000-year-old Chinese text, Shen Nong Ben Cao Jing (Divine Husbandman's Classic of the Materia Medica).
In Chinese medicine, Astragalus is prescribed for various forms of insufficient qi. It has a marked effect on the immune system of humans and rodents and has been clinically studied in China as an adjuvant for chemotherapy. The common daily dose in noncancer conditions is 9 to 30 grams of dried herb in decoction. In exceptional cases, up to 60 grams per day may be given.39 When treating cancer patients in China, clinicians commonly prescribe a dose of roughly 30 to 60 grams per day.
The toxicity of Astragalus membranaceus is very low; oral doses of 75 to 100 g/kg did not cause acute toxicity in mice.40 Although side effects are minimal at normal doses, higher doses of Astragalus (and many of the other herbal immunostimulants discussed here) may cause insomnia, increased heart rate, palpitations, hypertension, a general feeling of overstimulation, or all of these.
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