Ashwagandha: Clinical Evidence on the Adaptogen

Ashwagandha (Withania somnifera) has been used in Ayurvedic medicine for millennia as a rasayana — a restorative remedy. Over the past 15 years the plant has become the subject of randomized clinical trials. Effects once described as "enhanced vital energy" can now be mapped to specific biomarkers.

What is an adaptogen and how does ashwagandha work

An adaptogen is a substance that, according to its pharmacological definition, helps the body maintain homeostasis under stress without a specific mechanism of action. The active components of ashwagandha — withanolides — interact with the hypothalamic-pituitary-adrenal (HPA) axis, which governs cortisol release. In trials this manifests as a reduction in inflammatory markers and normalization of the hormonal response to chronic stress.

It is important to distinguish between product forms: the largest evidence base has been accumulated for standardized aqueous root extracts (KSM-66, Sensoril), not for leaf powder or non-standardized preparations. It is precisely the extracts with a known withanolide content that were used in the majority of significant trials.

Cortisol and perceived stress: what the meta-analyses say

The most reproducible effect of ashwagandha is a reduction in cortisol. In the key double-blind RCT (Chandrasekhar et al., Indian Journal of Psychological Medicine, 2012) 64 adults with chronic stress took 300 mg of KSM-66 extract twice daily for 60 days. Serum cortisol fell by 27.9% in the treatment group versus 7.9% in the placebo group (p=0.0006).

A meta-analysis of 15 RCTs (873 adults; Bachour et al., BJPsych Open, 2025) pooled data from a broader base. The reduction in cortisol averaged 2.36 µg/dL (95% CI: −3.26; −1.46; p<0.0001). The Perceived Stress Scale (PSS) score simultaneously fell by 4.88 points (95% CI: −7.84; −1.91; p=0.0013). Hamilton Anxiety Rating Scale (HAM-A) anxiety by week 8 decreased by 3.52 points (95% CI: −6.00; −1.04; p=0.0053). The authors concluded that taking 300–600 mg of ashwagandha per day for 8–12 weeks produces statistically significant changes across all three measures.

Is there an effect on quality of life?

A separate finding from the same meta-analysis: quality-of-life scores did not show statistically significant improvement (p=0.37). This does not mean quality of life does not change — rather, that heterogeneity of protocols and small samples do not allow this more subjective outcome to be captured with confidence. But keeping this fact in mind when formulating expectations is important.

How ashwagandha affects athletic performance

Interest in ashwagandha extends beyond stress management. A meta-analysis of 8 RCTs (Jayawardena et al., Turkish Journal of Sports Medicine, 2025) showed: ashwagandha significantly improved VO2max in trained individuals — by an average of +4.09 mL/(min·kg) (95% CI: 2.55–5.63; p<0.001). However, heterogeneity of results was high (I²=92%), and only 4 of the 8 studies entered the final analysis — which reduces the reliability of the overall estimate.

In a separate double-blind RCT (Raut et al., Cureus, 2024) 27 healthy men took 500 mg of extract per day for 60 days. The total distance covered on a cycle ergometer in the intervention group was 2.85 ± 0.54 km versus 2.16 ± 0.62 km in controls (p=0.001) — an increase of approximately 32%. Differences in muscle strength and body mass in the same study did not reach statistical significance.

What limits the conclusions

Several factors call for cautious interpretation. Most trials enroll 20–100 participants and last no longer than 12 weeks — long-term data are scarce. Study quality is uneven: only 25% of the studies included in the sports meta-analysis received a high PEDro score. Some studies were funded by manufacturers of standardized extracts, which is a potential source of bias.

On safety: within the studied doses and timeframes, standardized extracts are considered well tolerated. Rare cases of hepatotoxicity have been reported in the literature for non-standardized forms — an argument in favor of certified products and moderate doses.