Withania somnifera (of the family Solanaceae) is a highly esteemed medicinal herb in Ayurveda and is most popularly known as ashwagandha, although other common names include the King of Ayurveda,^[79][80] Indian ginseng (not related to Panax ginseng), and wintercherry.^[81] The herb is classified as rasayana in Ayurvedic medicine, which suggests it has the ability to affect health, wellness, and vitality. It is also classified as bhalya (increases strength) and vajikara (aphrodisiac).^[82] In modern terms, it is called an adaptogen for similar reasons.^[37]

Beyond those uses, it has been traditionally used as an analgesic, astringent, antispasmodic, and immunostimulant while being used to treat inflammation, cancer, stress, fatigue, diabetes, and cardiovascular complications.^[83][84] The adaptogenic properties of ashwagandha have been emphasized for treating people with stress-related insomnia, debility, and nervous exhaustion.^[85] Ashwagandha has also been reported to have immunostimulant properties that may help to mitigate the negative effects of stress on the immune system.^[85]

Ashwagandha has shown mixed effects on hormone health measures such as cortisol, testosterone, estrogen, luteinizing hormone, follicle-stimulating hormone, prolactin, and thyroid hormones in human studies.

In chronically stressed adults who take ashwagandha (300–500 mg for 60–90 days), cortisol was reduced by 20% to 50% from baseline values, and the effect was higher for those with higher levels of stress.^[13][14]

Ashwagandha’s effects on hormones are not limited to cortisol. Preliminary evidence suggests that 500 to 600 mg of ashwagandha root extract per day may increase testosterone levels in men when taken for 3 to 6 months. Improvements in testosterone levels, luteinizing hormone, follicle-stimulating hormone, sperm quality parameters, quality of life, and sexual functioning have been seen with ashwagandha use.^{[21][7][22][23][24][20]} Effects on testosterone are more pronounced in men with infertility and low testosterone levels, though ashwagandha may also boost testosterone levels in men without infertility or low testosterone as well.^{[25][26][22][27][23][14]} Ashwagandha enhanced seminal parameters in infertile men (e.g., sperm count, motility, quality, and vitality), suggesting that it may help to improve fertility. It’s possible that increases in seminal antioxidant capacity may be partially responsible for these effects.^{[14][23][20][24]}

Ashwagandha may also have beneficial effects on hormone health in women. Though current evidence suggests these beneficial effects are less pronounced than those seen in men, there still isn’t enough evidence to say this conclusively. Ashwagandha apparently also improves sexual function in women, but it’s not clear yet whether subjective well-being is similarly enhanced.^[86] One study did find that ashwagandha use in menopausal women increased estrogen levels while simultaneously lowering follicle-stimulating hormone and luteinizing hormone levels to produce an overall improvement in menopausal symptom-related quality of life.^[28]

Because stress levels are associated with neuroendocrine function, ashwagandha may affect general mental and brain health by reducing stress.^{[87][88][89][90]} In studies where ashwagandha improved subjective signs and symptoms of stress, factors such as anxiety, cognition, and sleep quality also improved, along with cortisol.^{[30][9][10][12][8]} It should be noted that the efficacy of ashwagandha is more pronounced in people reporting both a negative health state and high stress levels.^[91][13] Effectiveness for sleep has been mirrored in some human studies, where a significant increase in sleep quality (among other sleep related parameters such as improvements in sleep latency, sleep efficiency, sleep duration, alertness, and reduced sleep disturbance) occurred when ashwagandha (120–700 mg) was taken daily for periods ranging from 1 to 3 months.^{[18][16][5][17][19]} It should be noted, however, that prior studies using higher doses of ashwagandha extract (750–2,000 mg, alone or combined with other herbs) did not result in further significant improvements in sleep.^[92][93][94]

Ashwagandha’s potential to influence the HPA axis and affect neurotransmitter activity may explain some of its proposed effects on mental health, but more research is needed to better understand the underlying mechanisms.^[51] In human studies, 200 to 400 mg of ashwagandha daily over the course of 30 to 60 days reduced symptoms of depression in participants with elevated levels of stress.^[25][30]

Ashwagandha may also exert some anxiety-reducing effects as a result of the antistress properties. Lower doses of ashwagandha also appear to increase the effects of some anxiolytics, including alcohol.^{[95][96][97][98][99][100][101][102][103]} Reduced anxiety has been observed with dosages from 300 mg to 12,000 mg per day of ashwagandha over periods ranging from 4 to 8 weeks. For general stress reduction that hasn’t reached the point of diagnosed anxiety, 300 to 600 mg daily appears to be sufficient.^{[9][31][13][1][32][33][34]}

Ashwagandha may have beneficial effects on brain health by promoting the formation of neurons and enhancing neuroprotection, but the clinical evidence is somewhat mixed. In studies where ashwagandha (200–400 mg daily for 1–3 months) enhanced CNS activity and cognition, other factors such as cortisol, quality of life, sleep quality, and subjective measures of stress also improved, as would be expected. However, outcomes such as appetite, anxiety symptoms, short-term memory, serum BDNF, impulsivity, and alertness also saw some benefits in these studies, but to a much lesser extent that can’t be generalized to the broader population at this time.^{[30][35][10][36][37][38]}

It is uncertain whether ashwagandha affects immune health by reducing stress, but chronic stress tends to suppress immune function.^{[104][89][51]} Ashwagandha’s general immunomodulatory capability (at a dosage of 60–500 mg daily for 1–4 weeks) has been explored through direct assessment of immune parameters (immunoglobulin A, immunoglobulin M, immunoglobulin G, cytokines, natural killer cells, and lymphocytes) with encouraging results for fighting infection.^{[4][105][56][106][107][108]} These findings, however, still require replication with more robust methodological approaches.

When examining the prevention or treatment of respiratory infection, studies tended to take a more complete ayurvedic approach by using ashwagandha alongside additional therapies and/or herbs. Although these studies have promising initial results, the methods and interventions used were variable, and more research is needed.^{[105][109][110][107][108]}

A few clinical trials in adults with and without health conditions appear to suggest that antioxidant and anti-inflammatory properties provide the main effects on immune health. Ashwagandha use (500–5,000 mg daily for 8–12 weeks) correlated with increases in antioxidants and decreases in oxidation markers such as malondialdehyde, along with improvements in exercise recovery, fertility, lung function, oxygen uptake, perceived stress, and quality of life.^[11][20][43] Several studies have also explored ashwagandha (500–1,000 mg daily for 8–12 weeks) for treating arthritis, where anti-inflammatory capacity was the proposed mechanism of action, though this mechanism and effect still has yet to be confirmed.^{[111][112][113]}

Oral supplementation of ashwagandha in people with no health conditions appears to improve cardiorespiratory parameters during exercise, notably VO₂max.^[48] Increases in power output in sedentary people with no health conditions who start resistance training (750–1,250 mg of ashwagandha daily for one month) and also those who undergo no training (600 mg of ashwagandha daily for two months) have been reported.^[94][26] Ashwagandha (120–1,250 mg daily for 2–12 weeks) reportedly also improves VO₂max, upper body strength and lower body strength, lower body power, and recovery in both trained and untrained athletes.^{[6][45][46][47][48][11][5][26]} Ashwagandha has also been shown to improve endurance performance by increasing levels of hemoglobin^[6] (the protein in red blood cells responsible for transporting oxygen to the rest of the body), but more studies are needed to confirm this effect. Ashwagandha (600–1,250 mg daily for 1–2 months) in sedentary people with no health conditions may increase lean mass and decrease fat mass, but the results thus far have been mixed.^[94][26]

Ashwagandha has no clear influence on blood pressure in people without pre-existing health conditions, but the evidence is limited.^[48]

A reduction in LDL cholesterol has been seen in people with no health conditions who took ashwagandha (750–1,250 mg for one month), though there was no indication of changes in triglycerides in these same individuals over the same period.^[94] A mild reduction in triglycerides has been associated with oral ingestion of ashwagandha when taken by people with metabolic syndrome.^[94][114]

Similarly, there appears to be a mild reduction in blood glucose with ashwagandha use (1,200 mg daily for 30 days) by people with metabolic syndrome (insulin resistance).^[114]

Cancer therapy is a newer frontier for exploring ashwagandha as a potential therapy. Preclinical studies on withaferin A (an isolated constituent of ashwagandha) indicate it may inhibit or control cancer metastasis in animal and cell models.^{[115][116][117][118]} In humans undergoing chemotherapy for breast cancer, ashwagandha as a whole-herb supplement has demonstrated an increase in well-being and physical/emotional function, and a reduction in fatigue, insomnia, and pain.^[91]