Family

Fabaceae.

Related Species

Astragalus membranaceus var. mongholicus (Bunge).

Habitat and Cultivation

Perennial member of the legume family, native to Northern China, Mongolia, and Siberia and now under organic cultivation in the United States. The genus contains more than 400 species. Wild “locoweeds” (various Astragalus spp.) are a common livestock forage food. Gum tragacanth is derived from a related species, A. gummifer .

Parts Used

Radix (root).

Common Forms

• Dried Sliced Root:   Often soaked, then pressed or flattened; variant preparation may be honey-roasted in Chinese medicine.

• Powdered Root:   For decoction, liquid extracts and tablets.

• Tincture and Fluid Extracts:   60% to 70% ethanol; usually include a water-extraction phase for polysaccharides, then preserved in ethanol.

• Standardized Extracts:   Several preparations are available. There is no consensus on marker compounds for standardization at this time; individual manufacturers’ preparations may vary.

Overview

Astragalus has been used for more than 2000 years in Chinese medicine and is one of several important materia medica imports into Western botanical medicine. The herb is primarily used in Western herbalism as an immunomodulating agent and for cardiovascular disease. Interest in the herb as an adjunct to chemotherapy in oncological settings is increasing, but a recent Cochrane review found limited evidence of value for astragalus decoctions in improving adverse effects of chemotherapy in colorectal cancer patients. ¹ Another, more recent meta-analysis reviewed trials in which astragalus was combined with platinum agents in non–small cell lung cancer; evidence showed that the combination may provide increased effectiveness in terms of tumor response, reduced toxicity of the chemotherapy, survival time, or performance status. ²

Most available scientific literature is published in Chinese and has not been directly accessed for this survey. Much of the experimental data on astragalus are based on isolated polysaccharide fractions, either in vitro or by intraperitoneal administration in vivo. Extrapolation from this data to human oral consumption of powdered crude herb or liquid extracts may not be appropriate, particularly with regard to dosage. Chinese clinical trials usually use the herb in combination formulae with other herbs, such as ginseng, dang gui, poria, and rhemannia, because this is the typical manner of clinical administration. The available data have been used to discuss the interactions later.

Astragalus, as with other East Asian herbs incorporated into the Western materia medica relatively recently, is not monographed by the German Commission E, European Scientific Cooperative on Phytotherapy (ESCOP), or World Health Organization (WHO). Astragalus does have an American Herbal Pharmacopoeia monograph, ³ and the literature has been reviewed by McKenna et al. ⁴ and Wagner et al. ⁵ Bensky et al. ⁶ provide an authoritative review, and Chen and Chen ⁷ relate traditional Chinese uses to conventional pharmacology.

Historical/Ethnomedicine Precedent

Chinese uses include spleen (Pi) qi tonification, lung (Fei) qi tonification, and “securing the exterior”; promoting pus discharge and growth of new tissue and providing immune support. These features may contribute to a number of different biomedical pathological conditions. Astragalus is traditionally used in Chinese medicine in combination formulae for a wide range of conditions, from the common cold to chronic renal failure. ⁷

Known or Potential Therapeutic Uses

Cardioprotection (anti-ischemic, fibrinolytic, antioxidant); immunostimulation (reversal of leukopenia, myelosuppression); general prophylaxis of infection, stress, hypertension, certain viral infections (coxsackieviruses B2 and B3, parainfluenza type 1, viral myocarditis, Japanese endocarditis, HSV-1), nephritis, nephropathy, oxidative stress psoriasis, prostatic hypertrophy, and Takayasu arteritis.

Key Constituents

Polysaccharides (astragalans or astragologlucans); triterpene saponins (astragolides I-VII); isoflavones and other flavonoids; amino acids, minerals, essential oils, and phytosterols.

Therapeutic Dosing Range

• Dried Root:   10 to 15 g daily; by decoction, maximum 120 g in Chinese medicine.

• Hydroethanolic Extracts:   10 to 20 mL daily (based on 1:1 equivalent).

Strategic Considerations

Astragalus is used in Western botanical medicine as a tonic, adaptogenic, immunomodulating herb with negligible toxicity. It is myeloprotective, with added cardioprotective, hepatoprotective, and antioxidant properties, which make it a potentially useful adjunct in contexts involving immunosuppression, whether through disease processes, such as human immunodeficiency virus (HIV) and chronic fatigue immune dysfunction syndrome (CFIDS), or drug induced, such as myelosuppressive chemotherapies for the treatment of malignancies and immunosuppression in allograft patients. Recent research on the cardiac properties of the herb may help expand the Western use of astragalus beyond the narrow confines of “immunomodulation.” ^9,10

Astragalus use with pharmaceutical immunosuppression (i.e., allograft patients) may be theoretically problematic, but there are no reports of adverse interactions arising from its use in this context. Combination with immunosuppressants may be regarded as contraindicated in practice. Several interactions described later are based on pharmacodynamic effects of the herb on immune parameters. These interactions are not generally supported by published clinical trials; however, strategic coadministration of the herb in some of the therapeutic contexts described is anecdotally established practice among some practitioners of botanical and integrative medicine.

Effects on Drug Metabolism and Bioavailability

There is currently no evidence of interactions resulting from the effects of astragalus on drug-metabolizing systems. A rodent study examining the hepatoprotective effects of astragalus saponins against acetaminophen-induced toxicity found a significant increase in hepatic cytochrome P450 (CYP) levels after astragalus administration. ¹¹ Although studies are lacking, clinically significant pharmacokinetic interactions have not been reported to date.

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