Withania somnifera

Withania somnifera, evergreen shrub in the nightshade family (Solanaceae), native to India, North Africa, and the Middle East, that is used in traditional systems of medicine, particularly Ayurvedic medicine in India, where it is known as ashwagandha. A Sanskrit term, ashwagandha translates to “smell of the horse,” in reference to the odor of its leaves. Withania somnifera is also cultivated in other parts of the world and is popular as a dietary supplement. However, scientific evidence supporting claims about its health benefits is lacking.

W. somnifera is a branching shrub that favors dry sunny climates, being hardy and drought-tolerant. It typically grows to about 3 feet (1.5 meters) in height and produces green-yellow flowers and orange-red berries, which are poisonous. Its leaves are simple and ovate and have a downy covering of hair, giving them a pale sheen. Under cultivation, W. somnifera can be propagated from cuttings or seeds; it thrives in sun to partial shade, in dry loose soil.

Various parts of W. somnifera, including its leaves, berries, seeds, and especially roots, are used in traditional systems of medicine. These parts contain bioactive compounds, predominantly alkaloids, saponins, and steroids known as withanolides. Other substances that have been isolated from W. somnifera include amino acids, flavonoids, glucose, glycosides, and tannins. These compounds and their metabolites are thought to underlie the claimed health benefits that are associated with ashwagandha.

Ashwagandha is often referred to as an adaptogen, a substance believed to help the body cope with stress. In Ayurveda and as a supplement, it is used for a variety of conditions. Some examples are anxiety, depression, diabetes, elevated blood glucose, fatigue, inflammation, insomnia, male infertility, rheumatoid arthritis, and stress. However, many of these claims are supported by limited scientific evidence. Moreover, although generally well tolerated, ashwagandha is associated with several potentially dangerous side effects, including liver injury and sedation. Because ashwagandha may increase testosterone levels, it may be harmful for men with hormone-sensitive prostate cancer.

In the United States ashwagandha is a dietary supplement and therefore is exempt from the strict regulations placed on prescription medications. In 2023 ashwagandha was banned in Denmark following a study that found that the plant may have harmful effects on thyroid and sex hormone levels and may induce abortion.