Ashwagandha (Withania somnifera), also known as Indian ginseng, is an herb used in Ayurveda, the traditional medicine of India. Its root has a horsey smell and is said to confer the strength and virility of a horse. In Sanskrit, ashva means “horse” and gandha means “smell.”^[8] Various parts of the plant are used, but the most common supplemental form is an extract of its roots. Its use as part of the Ayurvedic system usually involves more than just the herb alone.

Ashwagandha is classified as an adaptogen, meaning it’s purported to enhance the body’s resilience to stress. Rodent and cell culture studies suggest that ashwagandha may provide a wide range of health benefits,^[9][10] but evidence in human studies has thus far varied depending on the health state and population of interest. ^{[11][12][13][14][15][6]}

Ashwagandha is best known for its anxiolytic (anti-anxiety) and stress-relieving effects.^{[16][17][18][19][20]} It also seems to reduce cortisol levels.^{[8][21][18][19][22][20]} In addition, a growing body of evidence supports the efficacy of ashwagandha for improving total sleep time and sleep quality in people with and without insomnia.^[5]

Since the stress response has a wide range of effects on the human body, it is possible this action is where ashwagandha’s reputation for being a ‘cure all’ originated. There is increasing support for the use of ashwagandha in the context of health states that are typically affected by a chronic stress response.^[23] Ashwagandha research in cardio-respiratory and musculoskeletal performance enhancements has shown promise for both athletes and non-athletes.^{[24][25][26][27][28][15][6]} Similarly, ashwagandha may also improve immune health, women’s health, men’s health, and sexual health. Unfortunately, due to inconsistencies in the research, it has been difficult to form any direct conclusions.^{[29][4][30][31][32][33][7][34]}

Ashwagandha appears to be safe, but more long-term research specifically designed to evaluate its safety is needed. Ashwagandha may cause mild drowsiness and sedation for some people.^{[35][36][10][37]}

Some case reports have suggested adverse effects such as rash or thyroid dysregulation may occur with ashwagandha use, but the same has not yet been observed by safety studies with larger samples.^[38][39][35] Several case reports have also raised concerns regarding the rare occurrence of liver toxicity with ashwagandha use, but similarly, toxicity has not been observed in clinical safety trials. In the reports, liver toxicity was usually reported within 2–12 weeks of ashwagandha use, and liver function returned to normal in all but one case following medical support and ashwagandha discontinuation.^{[40][41][42][43][44][45]} An in vitro study suggested that withanone (one type of withanolide in ashwagandha), may have toxic effects in the context of low levels of the cellular antioxidant glutathione (GSH), which is involved in drug detoxification.^[46] However, this research is far from conclusive and the mechanisms underlying this possible adverse effect are unclear.

Ashwagandha contains numerous bioactive compounds, namely alkaloids, flavonoids, glycosides, steroids, and steroidal lactones.^[10] Within the steroidal lactones are withanolides, which are considered to be responsible for most of the plant’s benefits.

A prevailing theory that is proposed to explain ashwagandha’s effects in humans involves the plant’s influence on the hypothalamic-pituitary-adrenal (HPA) axis as evidenced by its ability to affect cortisol levels.^[47]

Current evidence on the effects of ashwagandha in humans tends to implicate the HPA axis. A majority of the related studies focus on stress and stress-related conditions, which are frequently tied to cortisol, other neuroendocrine hormones, and neurotransmitters. Much research has been devoted to understanding the ability of ashwagandha to mitigate the effects of both healthy and detrimental stress, which, in turn, could affect other outcomes and or health states. Anxiety, depression, fertility, obesity, sleep, exercise recovery, immune health, and cognition are just a few examples. The HPA stress response may also explain some of the varied results seen in the body of evidence. This variance could be the result of ashwagandha affecting the HPA axis differently in different people. It may also be due to the complex relationship between stress and health conditions. If stress isn’t the precipitating factor for a negative health state, ashwagandha may not be an effective treatment for it either.

The strongest evidence to date suggests ashwagandha has cortisol and corticosteroid lowering effects.^{[47][8][21][18][20][22][19][48][49][50]} In studies where cortisol was lowered, other outcomes, such as anxiety, weight management, fertility, cognition, sleep, and/or quality of life, have also shown some improvement.^{[22][19][49][21][48][8][18][20]}