≥ 600 mg/day of standardized root extract (e.g., KSM-66 or Sensoril), for at least 8 weeks. It is usually taken with food.
Reduces perceived stress and lowers cortisol compared with placebo in 6–8 week trials.
View the study (systematic review) →In chronic stress it modulates the HPA axis: lowers morning cortisol (5–8 μg/dL), increases DHEA-S and reduces markers of allostatic load. One of the adaptogens with the most clinical evidence for this effect.
View the study (several RCTs) →Improves anxiety symptoms; a consistent signal although with small studies.
View the study (systematic review) →Reduces HAM-A scores in mild-to-moderate GAD at 6–8 weeks. A smaller effect than Silexan or kava but with an overall anxiolytic profile (stress + sleep + mood).
View the study (systematic review) →Improves sleep quality, especially in people with insomnia.
View the study (systematic review) →Small increases in testosterone and strength in men who train; modest effect.
View the study (clinical trial) →⏱ 3 min read
Ashwagandha (Withania somnifera) is probably the most clinically studied adaptogen from the Ayurvedic tradition, and the flood of trials published in the last decade has consolidated a fairly well-defined profile: it acts mainly on the cortisol axis and the autonomic nervous system, with modest but replicable effects on perceived stress, sleep quality, and, in some contexts, testosterone levels in adult men.
The main active constituents are withanolides, a family of plant steroids that appear to modulate GABA receptors and the activity of the hypothalamic-pituitary-adrenal axis, which is why standardized extracts (typically 5 percent or more withanolides) are the ones used in the clinical trials that generated the dosing recommendations and established the safety profile that guides its use today.
The most consistent evidence for ashwagandha is its effect on cortisol and perceived stress: several randomized trials with 600 milligrams daily of root extract (typically KSM-66 or Sensoril, the two brands with the most studies) for 8 to 12 weeks have shown reductions of 20 to 30 percent in morning cortisol and significant subjective improvements on standardized perceived-stress scales such as the Perceived Stress Scale.
The effect is comparable to that of some mild anxiolytics without the associated risks, and the response usually appears from the fourth week of continued use, not in the first doses; anyone seeking immediate relief from acute stress will not find a magic pill, but anyone who takes it for several weeks in a context of demanding work or life stress may notice a real improvement in their ability to tolerate pressure without becoming emotionally overwhelmed.
Multiple independent studies have documented improvements in sleep quality with doses of 300 to 600 milligrams daily, especially in people with mild insomnia or non-restorative sleep, with effects on sleep latency, efficiency, and the morning feeling of rest; these effects are not as pronounced as those of melatonin for jet lag or of valerian in some cases, but ashwagandha has the advantage of combining it with a reduction in daytime cortisol.
In clinically diagnosed anxiety, the evidence is somewhat more limited but points in the same direction: significant symptom reduction on scales such as the Hamilton Anxiety Rating Scale, with a very favorable safety profile that makes it especially attractive for people who prefer to avoid pharmacological anxiolytics because of the risk of dependence or their sedating effects during the day.
Several trials in healthy adult men have shown modest increases in total and free testosterone (on the order of 10 to 15 percent) with 600 milligrams daily for 8 to 16 weeks, along with improvements in strength, muscle mass, and body composition when combined with resistance training; an effect on male fertility (sperm motility and concentration) has also been reported in men with idiopathic subfertility.
The magnitude of the changes is clinically modest and is not equivalent to hormone replacement therapy, but in men with testosterone levels in the low-normal range it can be a reasonable adjunct within a broader protocol that includes strength training, sufficient sleep, stress control, and healthy body composition, all of which have a greater cumulative impact than any isolated supplement.
The effective dose in trials is 300 to 600 milligrams daily of standardized extract, ideally with a meal and for at least 8 weeks to assess individual response; products bearing the KSM-66 or Sensoril seal are the best supported by direct clinical evidence, which does not mean other brands do not work but does mean that quality and standardization are less guaranteed in generic products.
The most important precautions are pregnancy and breastfeeding (where it is not recommended because of insufficient data), people with thyroid disease (because it can raise thyroid hormones and precipitate hyperthyroidism), those taking immunosuppressants (a theoretical interaction), and those with active liver disease, because rare cases of hepatotoxicity associated with prolonged use or contaminated products have been reported.
Information, not medical advice. Scientific evidence reflects the quality of the studies.