Check · Supplements · Ashwagandha In review

Does ashwagandha lower stress and cortisol, improve sleep, and boost testosterone?

Claim attributed to Supplement industry, makers of branded extracts KSM-66 (Ixoreal Biomed), Sensoril, and Shoden (Arjuna Natural), widely amplified across wellness and fitness media. , A bundle of three sub-claims of unequal strength; marketing presents them as equally settled, which overstates the sleep and testosterone evidence.

Verdict Mixed

Evidence grade C Low certainty

Three claims, three strengths. The cortisol drop is real and replicated; the sleep benefit is modest; the testosterone boost is small, inconsistent, and confounded by exercise. Presenting all three as equally proven is misleading.

It is a genuine cortisol-lowering herb sold on a testosterone promise the trials never actually established.

The theory

What it’s supposed to target

HPA axis / cortisol
Stress + anxiety response
Sleep
Testosterone (secondary claim)

Ashwagandha (Withania somnifera) is an adaptogen, a herb proposed to blunt the body's stress machinery. The leading mechanism centers on the HPA axis (hypothalamic-pituitary-adrenal), the loop that releases cortisol under stress. Its active withanolides are thought to dampen that signaling, lowering cortisol and the felt sense of stress, with knock-on benefits for sleep and, the further-reaching claim, for testosterone (since chronic stress and poor sleep suppress it).

Of the claims, the stress-and-anxiety one has the most support: multiple small randomized trials show lower perceived stress and cortisol. Sleep benefits are modest, and the testosterone story is the weakest, small rises in small studies, often alongside exercise. The catch is who runs the trials: most are small, short, and funded by the makers of branded extracts, which tends to inflate the effect, and rare liver-injury reports mean it is not risk-free. A genuine calming signal, oversold once it reaches the testosterone-booster aisle.

Mechanism is theory, not proof. A plausible pathway explains why something might work, not whether it does. The verdict rests on the evidence below, not the elegance of the theory.

The claim

What would have to be true

Ashwagandha lowers serum cortisol: holds, well-supported in short trials.

Lower cortisol translates into lower felt stress: holds only partly; the biomarker is steadier than the subjective effect.

It improves sleep: holds but modestly, mainly in diagnosed insomnia.

Lower cortisol raises testosterone in humans: unproven; data are byproducts of stress or exercise studies and inconsistent.

The evidence

What the evidence actually shows

The cortisol signal is the strongest, and it holds

Across multiple small randomized trials, ashwagandha lowers serum cortisol. Chandrasekhar 2012 (n=64, 60 days, KSM-66 600 mg/day) reported a 27.9% fall in cortisol (vs 7.9% on placebo) and a 44% drop in the Perceived Stress Scale (vs 5.5% on placebo). Lopresti 2019 (n=60, Shoden 240 mg/day) found morning cortisol down 23% versus +0.5% on placebo (P<0.001). A 2025 BJPsych Open meta-analysis of 15 RCTs (n=873) pooled a significant 8-week cortisol reduction (mean -2.36, P<0.0001) and lower anxiety, though it found no improvement in quality of life, and an independent review reported cortisol falling while perceived stress did not. The biomarker is more consistent than the felt benefit.

Sleep is modest; testosterone is weak and confounded

A 2021 PLOS One meta-analysis (5 RCTs, n=400, all India) found a small-to-moderate sleep benefit (SMD -0.59), larger in diagnosed insomnia and at doses at or above 600 mg/day, but with moderate-to-high heterogeneity (I2=62%). On testosterone, Wankhede 2015 (n=57 untrained men) showed a greater rise (+96.2 vs +18.0 ng/dL, P=0.004), but both arms also did resistance training, so the hormone effect is entangled with exercise. Lopresti 2019 saw an 11.4% within-group rise in men that was not significant between groups (P=0.158). NIH LiverTox rates ashwagandha category B (likely cause of clinically apparent liver injury), with roughly 23 reported cases and rare liver failure.

Evidence quality

Studies, graded, and who paid

Lowers serum cortisol short-term B Moderate certainty

Replicated across many small RCTs; pooled 8-week cortisol drop significant in a 15-trial meta-analysis.

Lowers perceived (subjective) stress C Low certainty

Often significant, but at least one independent meta-analysis found cortisol fell while perceived stress did not.

Improves sleep C Low certainty

Small-to-moderate benefit, largest in diagnosed insomnia at higher doses; moderate heterogeneity, India-only trials.

Boosts testosterone D Very low certainty

One signal entangled with resistance training; non-significant between groups in another trial. No dedicated hypogonadism RCT.

Cited studies with type, size, funding/conflicts, and limitations.
#	Study	Type	Size	Funding / COI	Key limitations
64	Chandrasekhar 2012, stress/cortisol RCT	Double-blind placebo-controlled RCT	n=64, 60 days	Industry-funded Used branded KSM-66 extract supplied by Ixoreal Biomed; paper prints nil-COI, a foundational KSM-66 marketing trial.	Small, short, single-site; commercial extract.
60	Lopresti 2019, stress/cortisol/testosterone RCT	Double-blind placebo-controlled RCT	n=60, 60 days	Industry-funded Funded by Arjuna Natural Ltd, which supplied the Shoden extract.	Small; testosterone non-significant between groups.
873	BJPsych Open 2025 meta-analysis	Systematic review and meta-analysis	15 RCTs, n=873	Mixed Pools predominantly small industry-linked branded-extract trials.	Inherits source-trial bias; no QoL improvement.
400	Cheah 2021 sleep meta-analysis	Systematic review and meta-analysis	5 RCTs, n=400	Independent Review unfunded, no competing interests; flags one included trial as manufacturer-sponsored.	All India; I2=62%; moderate quality.
57	Wankhede 2015 strength/testosterone RCT	Double-blind placebo-controlled RCT	n=57, 8 weeks	Industry-funded Used branded KSM-66 (Ixoreal); most-cited male-vitality result.	Both arms did resistance training: effect confounded.

Small, short, India-only trials on proprietary extracts, heavily manufacturer-funded: a pattern that inflates favourable findings across all three sub-claims.

See who funded the studies behind every Caveat check

Stay neutral

Unproven ≠ disproven

The testosterone claim is unproven rather than disproven: there is no dedicated independent hypogonadism trial, and current numbers are side-findings of stress and exercise studies.

The gap

Where claim and evidence diverge

Trials are small (n~50-80), short (4-12 weeks), almost all run in India on proprietary extracts. There is no long-term safety or hard-outcome data, and no large head-to-head.

Follow the funding

The money trail

The favourable literature is largely produced by the branded-extract makers: Wankhede 2015 and Chandrasekhar 2012 used KSM-66 (Ixoreal Biomed); Lopresti 2019 was funded by Arjuna Natural, maker of Shoden.

The most independent synthesis, the unfunded Cheah 2021 sleep review, is also the most guarded and flags manufacturer sponsorship in its included trials.

Bottom line

The honest read

For short-term stress, ashwagandha has the best case: it reliably lowers cortisol and often eases anxiety, with a modest sleep benefit in poor sleepers. The testosterone promise is the weakest link and should not be the reason to take it. Mind the category-B liver-injury signal.

Falsifiable

What would change this verdict

A large, independent, non-manufacturer RCT in hypogonadal men, with no concurrent training, showing a significant between-group testosterone rise.

Independent long-duration trials confirming sustained stress and sleep benefits and clarifying the true incidence of hepatotoxicity.

Receipts

Sources

Common questions