The Hook: You Probably Bought It for the Wrong Goal
Ashwagandha is often marketed as a strength and muscle booster. A new meta-analysis suggests the most consistent payoff may be somewhere else: aerobic endurance.
The paper, published in Nutrients in 2026 by researchers at Shaanxi Normal University and Sichuan Agricultural University, pooled randomized controlled trials of oral Withania somnifera and its effect on objective exercise performance. The results are promising, but they come with caveats you should know before spending money.
What the Researchers Actually Did
This was a systematic review and three-level meta-analysis. The team searched PubMed, Web of Science, the Cochrane Library, Embase, and SPORTDiscus from inception to 1 April 2026. They included randomized controlled trials comparing oral ashwagandha with placebo or control and reporting objective performance outcomes.
The final pool was modest: 13 trials, 599 participants, and 79 effect sizes. A three-level model lets researchers handle trials that report several outcomes without treating each one as independent. The team also reported 95% prediction intervals, GRADE certainty ratings, subgroup analyses, and dose and duration meta-regressions.
Participants were mostly young adults or athletes. Four trials were male-only, one was female-only, three were mixed-sex, and five did not fully report sex composition.
The Headline Number
Across all performance outcomes, ashwagandha improved results on average, with a Hedges' g of 0.47 (95% CI 0.25 to 0.69, p < 0.001). That is a moderate pooled effect.
The authors also flagged two cautions:
- Heterogeneity was substantial (I² = 60%), so results varied meaningfully between studies.
- The 95% prediction interval ran from -0.40 to 1.33. It crosses zero, so a future trial in a different context could plausibly find no benefit, or even a small negative effect.
The average looks good, but it does not guarantee a result for every lifter or athlete.
The Twist: Endurance Beat Strength
Exercise type was the clearest moderator of the effect (P_between = 0.006). The findings split like this:
- Aerobic endurance: the most consistent evidence, with g = 0.54 (95% CI 0.22 to 0.85, p = 0.002).
- Strength: effects were positive, but the authors described them as uncertain.
- Power and muscular endurance: too little evidence to draw conclusions.
The strength result is not negative. The data are simply less certain, and the "strength supplement" label is not as well supported as the endurance signal. If you want to build your bench press, this paper does not give you a confident green light. If you run, cycle, or row, the case is stronger.
The Dose Sweet Spot: 500-600 mg/Day
The authors identified 500-600 mg/day of extract as the most evidence-supported dose range. They stress that the dose analyses were hypothesis-generating, meaning they point to a pattern worth testing rather than proving an optimal dose.
The meta-regressions covered both dose and duration. The abstract does not give a specific timing protocol, such as pre-workout versus evening, so this paper cannot tell you when to take it. It also does not tell you which formulation is best. The authors list formulation standardization as a gap for future research.
Practical Takeaways
Who it may suit
- Endurance-focused athletes and recreational runners, cyclists, and swimmers curious about a supplement with a research signal.
- Young adults and athletes, who made up most of the sample.
A reasonable approach based on this paper
- Stay within the 500-600 mg/day extract range, as that is where the evidence clusters.
- Check your product label for how much extract you are getting, since the authors point to formulation differences.
- Track an objective measure, such as a time trial or a repeatable test, so you can see whether it works for you.
Who should be cautious or skip it
- Anyone buying it mainly for strength or power gains. The evidence here is uncertain or sparse.
- Anyone outside the studied population. Most data come from young adults and athletes, and the paper does not establish effects in older adults, adolescents beyond one athlete cohort, or other groups.
- People with medical conditions, those on medication, or those who are pregnant. The paper does not address these groups, and the authors call for better adverse-event monitoring in future trials. This is general caution, not a finding from the study, so talk to a clinician first.
Limitations You Should Not Ignore
The authors are candid about the weaknesses:
- Small evidence base. Thirteen trials and 599 people is not large, especially once split across outcome types.
- Moderate-to-high heterogeneity. An I² of 60% and a prediction interval crossing zero limit how confidently the average applies to any one situation.
- Hypothesis-generating dose findings. The 500-600 mg/day range is a lead, not a verdict.
- Incomplete reporting. Five trials did not fully report sex composition, so sex-specific conclusions are limited.
- Sparse data for power and muscular endurance.
The authors say future trials should be preregistered, adequately powered, double-blind, formulation-standardized, and sex-stratified. They also call for rigorous blinding checks, mechanistic endpoints, adverse-event monitoring, and sport-specific performance tests. The authors declared no conflicts of interest.
The Bottom Line
This meta-analysis suggests oral ashwagandha may improve selected exercise-performance outcomes, with the best evidence for aerobic endurance and a possible sweet spot of 500-600 mg/day. The strength claims that dominate supplement marketing are less certain. Treat ashwagandha as a promising, still-maturing option for endurance athletes, not a proven strength booster.
