Astragalus is a large genus of about 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to temperate regions of the Northern Hemisphere. Common names include milkvetch (most species), locoweed (in North America, some species) and goat's-thorn (A. gummifer, A. tragacanthus). Some pale-flowered vetches are similar in appearance, but vetches are more vine-like.
Astragalus species are used as food plants by the larvae of some Lepidoptera species including many case-bearing moths of the genus Coleophora: C. cartilaginella, C. colutella, C. euryaula, and C. onobrychiella feed exclusively on Astragalus, C. astragalella and C. gallipennella feed exclusively on the species Astragalus glycyphyllos, and C. hippodromica is limited to Astragalus gombo.
The natural gum tragacanth is made from several species of Astragalus occurring in the Middle East, including A. adscendens, A. gummifer, A. brachycalyx, and A. tragacanthus. Also Astragalus propinquus (syn. A. membranaceus) has a history of use as a herbal medicine used in systems of traditional Chinese medicine and Persian medicine. In traditional Chinese medicine A. membranaceus has been used to reinforce qi and strengthen the superficial resistance, and promote the discharge of pus and the growth of new tissue.
Biotechnology firms are working on deriving a telomerase activator from Astragalus. The chemical constituent cycloastragenol (also called TAT2) is being studied to help combat HIV, as well as infections associated with chronic diseases or aging. However, the National Institutes of Health states: "The evidence for using astragalus for any health condition is limited. High-quality clinical trials (studies in people) are generally lacking. There is some preliminary evidence to suggest that astragalus, either alone or in combination with other herbs, may have potential benefits for the immune system, heart, and liver, and as an adjunctive therapy for cancer".
Research at the UCLA AIDS Institute focused on the function of cycloastragenol in the aging process of immune cells, and its effects on the cells' response to viral infections. It appears to increase the production of telomerase, an enzyme that mediates the replacement of short bits of DNA known as telomeres, which play a key role in cell replication, including in cancer processes.
Extracts of Astragalus propinquus ( syn. A. membranaceus) are marketed as life-prolonging extracts for human use. A proprietary extract of the dried root of A. membranaceus, called TA-65, "was associated with a significant age-reversal effect in the immune system, in that it led to declines in the percentage of senescent cytotoxic T cells and natural killer cells after six to twelve months of use". There are mixed data regarding Astragalus, its effects on telomerase, and cancer. For example, although 80% of cancer cells utilize telomerase for their proliferation—a factor that might theoretically be exacerbated by Astragalus—the shortening of telomeres (resulting from such factors as stress and aging and possible contributors to malignancy), might also be mitigated by Astragalus. Thus, short telomeres result in chromosome instability, and the potential for telomere lengthening as a protection against cancer is possible. Additionally, scientists recently reported that cancer cells may proliferate precisely because of the lack of differentiation occurring via damaged or shortened telomere length. They propose that "forced" elongation of telomeres promotes the differentiation of cancer cells, probably reducing malignancy, which is strongly associated with a loss of cell differentiation.
Astragalus may interact with medications that suppress the immune system, such as cyclophosphamide. It may also affect blood sugar levels and blood pressure. Some Astragalus species can be toxic. For example, several species native to North America contain the alkaloid swainsonine, which may cause "locoism" in livestock. The toxicity of Astragalus taxa varies.
Several species, including A. alpinus (bluish-purple flowers), A. hypoglottis (purple flowers), and A. lotoides, are grown as ornamental plants in gardens.