Ashwagandha

ashwagandha · Withania somnifera · KSM-66

An adaptogenic herb promoted for stress, sleep and testosterone.

TypeSupplement / dietary

The grade answers: What does the human evidence support for: Stress & sleep?

Grade

Limited

The grade rates evidence quality — it is not advice to take or buy.

Class: Adaptogen
Primary use: Stress & sleep
Evidence strength: medium
Last reviewed: 2026-07-01

Bottom line

Reasonable short-term evidence for reducing stress and improving sleep; it is not a longevity molecule, and rare liver-injury reports mean it isn't consequence-free.

What the evidence says

Ashwagandha has a cluster of small randomized trials showing reductions in perceived stress and cortisol and improvements in sleep over 6–12 weeks, with some data on modest strength or testosterone changes in men. The effects are real but short-term and studied mostly with standardised extracts. It has no aging or longevity outcome data. Balanced against that are sporadic reports of drug-induced liver injury and thyroid effects. Grade C: a legitimate short-term stress/sleep aid, not a geroprotector and not risk-free.

Key studies

[1]
Ashwagandha for stress and anxiety (meta-analysis) · meta-analysis
Reduced perceived stress and cortisol short-term.
Open on PubMed ↗
[2]
Ashwagandha and sleep · RCT
Improved sleep parameters in small trials.
Open on PubMed ↗
[3]
Ashwagandha-associated liver injury (case reports) · safety
Rare but real hepatotoxicity signal to be aware of.
Open on PubMed ↗

See all studies on PubMed ↗

Scoped PubMed search, not a curated bibliography: the individual PMIDs for this entry have not yet been verified one by one. For that reason it is not used to support a high grade and is awaiting review.

Mechanism

Proposed modulation of the hypothalamic-pituitary-adrenal (stress) axis and GABAergic activity; withanolides are considered the active constituents.

Safety

Generally well tolerated short-term. Concerns include occasional GI upset, thyroid hormone changes, and rare but documented cases of liver injury. Avoid in pregnancy and with certain autoimmune/thyroid conditions without medical advice.

Dosage context

Trials typically use ~300–600 mg/day of a standardised root extract for 6–12 weeks. Long-term safety beyond a few months is not well characterised.

Examples of application

Taken as a standardised root extract (~300–600 mg/day) for short periods.
Aimed at stress and sleep, not longevity.
Watched for the rare liver-safety signal; avoided in pregnancy.

From the field

Ashwagandha is one of the better-evidenced adaptogens for stress — which is not the same as longevity. We grade it C and, unusually for a herb, flag a genuine (if rare) liver-safety signal.

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