The root of Ashwagandha (Withania somnifera) is used extensively in Ayurveda, the classical Indian system of medicine, and is categorized as a rasayana, an herbal remedy used to promote physical and mental health.
There are many claims concerning the health benefits of Ashwagandha root and most all of them concern reduction of adrenal stress (anxiety) and reduction of inflammation; there are many peer reviewed studies, including systematic review summaries that are rather convincing. Positive influences on neurodegenerative diseases such as cognitive decline and dementias have been suggested.
It is likely helpful to ingest this substance after exercise, particularly endurance workouts or heavy lifting (supposedly it helps to stimulate muscle recovery).
Also this Ayurvedic has been used to help treat insomnia.
The amount suggested by the literature studies is one-half teaspoon, about 1600 mg.
 Bhattacharya, S., Bhattacharya, A., Sairam, K., & Ghosal, S. (2000). Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: An experimental study. Phytomedicine, 7(6), 463-469. doi:10.1016/ s0944-7113(00)80030-6.
 Manchanda, S., Mishra, R., Singh, R., Kaur, T., & Kaur, G. (2016). Aqueous Leaf Extract of Withania somnifera as a Potential Neuroprotective Agent in Sleep-deprived Rats: A Mechanistic Study. Molecular Neurobiology Mol Neurobiol. doi:10.1007/s12035-016-9883-5.