thumb|Flower
Withania somnifera, known commonly as ashwagandha, is an evergreen shrub in the Solanaceae family that is native to the Middle East and North Africa, other African regions, southern Europe, Indian subcontinent, and across Southeast Asia. W. somnifera is commonly sold as a dietary supplement containing root or leaf powder or extracts. It is undergoing research for potential effects on stress, anxiety, and sleep, but current clinical evidence is insufficient to confirm its safety or efficacy. The primary phytochemicals in W. somnifera are withanolides—structurally similar to ginsenosides in Panax ginseng—along with alkaloids and sitoindosides, leading to its nickname, Indian ginseng.
Withania somnifera is generally well tolerated for up to about three months with mostly mild side effects.
Description
This species is a short shrub growing tall. Tomentose branches extend radially from a central stem. Leaves are dull green, elliptic, and usually up to long. The flowers are small, green, and bell-shaped. The ripe fruit is orange-red. The name ashwagandha is a combination of the Sanskrit words ', meaning "horse", and ', meaning "smell", reflecting that the root has a strong, horse-like odor. It prefers dry, stony soil with sun to partial shade. It can be propagated from seeds in the early spring or from greenwood cuttings in the later spring.
Diseases and pests
Withania somnifera is prone to several pests and diseases. Leaf-spot disease caused by Alternaria alternata is the most prevalent disease, which occurs in a severe form in Punjab, Haryana, and Himachal Pradesh. Leaf-spot disease reduces the concentration of its secondary metabolites. The leaves are also prone to Alternaria dianthicola in India.
A treehopper (Oxyrachis tarandus) feeds on the apical portions of the stem, making them rough and woody in appearance and brown in colour.
The carmine red spider mite (Tetranychus urticae) is the most prevalent pest of the plant in India. In recent years, this plant has been serving as a new reservoir host for an invasive mealybug species Phenacoccus solenopsis.
Phytochemistry
The main phytochemical constituents of W. somnifera are withanolides, a group of triterpene lactones that include withaferin A, alkaloids, steroidal lactones, tropine, and cuscohygrine. As these withanolides are structurally similar to the ginsenosides of Panax ginseng, W. somnifera is commonly referred to as "Indian ginseng". W. somnifera is commonly sold as a dietary supplement containing root or leaf powder or extracts.
Stress and anxiety
At oral doses of 300 to 600 mg per day over a three month period, ashwagandha root extract may be useful in treating generalized anxiety disorder, although the evidence for efficacy is tentative and the treatment may cause nausea and diarrhea.
Sleep
There is limited evidence that W. somnifera extract, especially at higher doses and over longer durations, may modestly improve sleep quality and related outcomes, with more noticeable effects in people with insomnia.
Adverse effects
Withania somnifera may cause adverse effects if taken alone or together with prescription drugs. The most common side effects include diarrhea, headache, sedation, and nausea.