Ashwagandha
Evidence: weak
Ashwagandha has more trials than most herbal supplements and a measurable VO2max signal, but the evidence is low quality: small studies, almost all from one region, mostly on branded extracts, with high heterogeneity and clear scope for publication bias. Its stronger case is stress and sleep, not direct performance.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Keep it in proportion
The basics are where the real gains are: consistent volume, sleep and adequate fuelling. Weigh anything below honestly, and do not let a marginal or over-marketed aid pull attention from the things that actually move the needle.
Ashwagandha (Withania somnifera) is a root used in Ayurvedic medicine and sold as an adaptogen, a supplement claimed to help the body resist stress. It is unusual among herbal ergogenic aids in having a real body of randomised trials and a couple of meta-analyses, which is why it warrants an honest page rather than a place on the weak-supplement shelf. The evidence looks more impressive at a glance than it does on inspection.
What the evidence shows
The headline endurance finding is a VO2max effect. A meta-analysis of trials in athletes and healthy adults found ashwagandha raised VO2max by a mean of 3.00 mL·kg⁻¹·min⁻¹ over placebo (95% CI 0.18–5.82, p = 0.04), but the confidence interval nearly reaches zero, heterogeneity was very high (I² = 84%), and the authors rated the overall evidence low by GRADE (Pérez-Gómez et al. 2020). A separate Bayesian meta-analysis across a dozen trials reported favourable effects on strength and power, cardiorespiratory fitness and recovery, framing ashwagandha as an adaptogen that may work partly by lowering cortisol (Bonilla et al. 2021). On paper that is a broader evidence base than menthol or nomio can claim.
Why the grade is still weak
The quality is thin in exactly the ways evaluating supplements warns about. The trials are small and short. Every study in the VO2max review was conducted in India, so the population is narrow. Most test standardised branded extracts, such as KSM-66, and the field is closely tied to the manufacturers that supply them, which is a funding pattern the marketing playbook treats as a caution rather than a disqualification. Heterogeneity is high, blinding is often unclear, and a literature of small positive trials is the classic setting for publication bias. A 3 mL·kg⁻¹·min⁻¹ VO2max change would be meaningful if real, which is precisely why it needs better support than it has.
The firmer signal is arguably not the running one at all. Ashwagandha’s effects on perceived stress, cortisol and sleep are its most consistent findings, and for a runner those matter mainly through sleep and recovery rather than as a direct ergogenic effect.
Safety
Ashwagandha is not a benign inert herb. It is hormonally active, with reported effects on thyroid hormones, and there are rare case reports of liver injury associated with its use. That, plus the fact that supplements are poorly regulated and variable in content, is reason for genuine caution rather than casual trial, and a reason to involve a doctor if it is being considered alongside medication or a thyroid condition.
The verdict
Ashwagandha is promising-looking, low-quality and heavily marketed. The VO2max meta-analysis is not nothing, but it is not the multiple large independent trials a confident recommendation would need, and the safety footnotes are real. If it earns a place for a runner, it is more likely through stress and sleep than through a direct performance effect, and it does not belong among the proven aids. Interesting, over-sold, unproven.