Adaptogens are a category of herbs from traditional Russian and Ayurvedic medicine that are claimed to help the body resist stressors. Most have thin evidence — a few small trials, a lot of marketing. Ashwagandha (Withania somnifera) is the exception. It has accumulated more than a dozen randomized, placebo-controlled human trials, and while many of them come from a small set of labs in India, the direction of the evidence is consistent enough to take seriously.
What the trials show
A 2012 randomized trial of 64 adults with chronic stress gave 300 mg of a high-concentration root extract twice daily for 60 days. The treated group showed a 27.9 percent reduction in serum cortisol versus 7.9 percent in placebo, and lower scores on the Perceived Stress Scale.1
A 2019 trial in healthy adults at a dose of 240 mg per day for 60 days found significant reductions in Hamilton Anxiety Rating Scale scores and morning cortisol.2 A separate 2019 trial focused on sleep gave 300 mg twice daily and saw improvements in self-reported sleep quality and modest objective sleep gains on actigraphy in adults with insomnia.3
A 2019 Australian study, run independently of the manufacturers that have funded much of the earlier work, gave 240 mg of a standardized extract per day for 60 days to adults with elevated stress. It found a small reduction in morning cortisol and improvements in DHEA-S and testosterone.4
The pattern across trials is modest effect sizes — reductions in stress and cortisol that are statistically significant and clinically noticeable, but not transformative. The two extracts with the most data are KSM-66 and Sensoril, which differ in standardization (root vs. root-and-leaf, different withanolide concentrations).
How to use it
The dosing range in trials is 300 to 600 mg per day of a standardized root extract, typically taken in one or two doses with food. Effects accumulate over four to eight weeks; this is not an acute compound. KSM-66 is the most-studied extract for stress and sleep outcomes.
The safety profile is generally good. The most common side effect is GI upset. Ashwagandha can mildly suppress thyroid function in some people and may augment thyroid hormone medications — people with hypothyroidism should consult a clinician. It is contraindicated in pregnancy and may interact with sedatives.
A small but real concern: case reports of hepatotoxicity have been published, including a series from European liver injury registries. The absolute rate appears low, but it is high enough that taking ashwagandha continuously for years without breaks is harder to defend than cycles of six to eight weeks at a time.
What it is not
Ashwagandha is not a substitute for sleep, exercise, or therapy. The cortisol effect is real but small relative to what an adequate sleep schedule does. The anxiolytic effect is meaningful in mild-to-moderate stress but not a substitute for clinical care in anxiety disorders. The testosterone effect in some trials is small and clinically uninteresting in healthy young men, despite the marketing around it.
It is, however, one of the few supplements in this category with enough randomized evidence to justify a trial in someone with chronic stress and disrupted sleep. The right framing is: a low-risk, moderate-evidence tool to layer on top of the basics, not a replacement for them.