Adjunctive Ashwagandha (Withania somnifera) Supplementation and Resistance-Training Adaptations in Healthy Adults: A Systematic Review and Random-Effects Meta-Analysis of Muscular Strength, Chest Circumference, and Body Composition.
Current evidence does not establish that adjunctive ashwagandha meaningfully enhances resistance-training adaptations; it indicates possible benefits for maximal strength and, indirectly, upper-body girth, but the evidence base is small, statistically fragile and of low to very low certainty, with no dependable effect on adiposity.
Key Findings
Results
Ashwagandha supplementation combined with resistance training was associated with greater gains in 1-RM bench press compared to placebo.
Pooled SMD (Hedges g) of 0.60 (95% CI 0.20–1.01) for upper-body 1-RM bench press
Three RCTs with n = 161 participants provided poolable data
Heterogeneity was low to moderate (I2 = 7–34%)
Under Hartung-Knapp-Sidik-Jonkman (HKSJ) adjustment, this estimate lost statistical significance
The result depended on one influential trial in leave-one-out sensitivity analysis
Results
Ashwagandha supplementation combined with resistance training was associated with greater gains in lower-body 1-RM strength compared to placebo.
Pooled SMD of 0.52 (95% CI 0.19–0.86) for lower-body 1-RM strength
Three RCTs with n = 161 participants provided poolable data
Under HKSJ adjustment, this estimate also lost statistical significance
This result similarly depended on one influential trial in sensitivity analysis
GRADE certainty was rated Low for this strength outcome
Results
Ashwagandha supplementation combined with resistance training was associated with greater gains in chest circumference compared to placebo.
Pooled SMD of 0.86 (95% CI 0.41–1.31) for chest circumference
Only two trials (k = 2) contributed to this pool
Under HKSJ adjustment, the confidence interval was described as 'too imprecise to be informative'
GRADE certainty was rated Very Low for chest circumference
The authors note this is an indirect measure of upper-body hypertrophy
Results
Ashwagandha supplementation combined with resistance training did not produce a statistically significant reduction in body fat percentage compared to placebo.
Pooled SMD of -0.32 (95% CI -0.72–0.08) for body fat, which crossed zero
GRADE certainty was rated Low for body fat
The authors concluded there was 'no dependable effect on adiposity'
Three RCTs with n = 161 participants contributed poolable data for this outcome
Methods
The systematic search identified only four eligible RCTs, of which one preprint could not be fully pooled due to uninterpretable bench-press values.
Twelve bibliographic sources and two trial registers were searched without date restriction up to 23 August 2026
Sources included PubMed/MEDLINE, Europe PMC, OpenAlex, and Cochrane CENTRAL
One preprint was reported narratively because its bench-press values were not interpretable as absolute loads
Embase, Scopus, Web of Science, and CINAHL were unavailable directly but accessed indirectly through CENTRAL
Reference-list, included-study-list, and forward-citation screening were also conducted
Results
All three pooled trials raised at least some concerns on Risk of Bias 2 (RoB 2) assessment.
Risk-of-bias assessment was conducted using the RoB 2 tool
Screening, extraction, and risk-of-bias assessment were performed independently in duplicate
No trial was rated as low risk of bias across all domains
GRADE certainty ratings were Low for bench press, lower-body strength, and body fat, and Very Low for chest circumference
The authors stated the evidence base is 'small, statistically fragile and of low to very low certainty'
Methods
The review was conducted without external funding and without prospective registration.
The authors explicitly state 'This review received no external funding and was not registered'
PRISMA 2020 guidelines were followed for reporting
Restricted maximum-likelihood random-effects models were used for pooling
Sensitivity analyses included leave-one-out and Hartung-Knapp-Sidik-Jonkman (HKSJ) adjustment
What This Means
This research suggests that taking ashwagandha (Withania somnifera) supplements while doing resistance training may produce slightly greater gains in upper- and lower-body strength and chest size compared to training with a placebo, but the evidence supporting these benefits is weak and unreliable. When researchers applied more conservative statistical methods (called HKSJ adjustment), the strength findings were no longer statistically significant, and each result was heavily influenced by a single study. The finding for chest circumference was based on only two studies and was too imprecise to draw conclusions from. Ashwagandha did not appear to meaningfully reduce body fat. Only three studies with a combined total of 161 participants could be pooled for analysis, and all had at least some methodological concerns.
This research suggests the current body of evidence is too small and fragile to confidently conclude that ashwagandha enhances the results people get from resistance training. The certainty of the evidence was rated as 'Low' for strength and body fat outcomes and 'Very Low' for chest circumference — meaning future research could easily change these conclusions. The authors emphasize that larger, independently funded trials using more direct measurements of muscle growth are needed before firm recommendations can be made.
For people who exercise and are considering ashwagandha supplements, this research suggests the popular marketing claims about ashwagandha dramatically boosting muscle and strength gains from resistance training are not yet supported by solid scientific evidence. While some promising signals exist, the database is too thin and methodologically limited to confirm a meaningful real-world benefit beyond what training alone provides.
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Lee J, Heo A. (2026). Adjunctive Ashwagandha (Withania somnifera) Supplementation and Resistance-Training Adaptations in Healthy Adults: A Systematic Review and Random-Effects Meta-Analysis of Muscular Strength, Chest Circumference, and Body Composition.. Nutrients. https://doi.org/10.3390/nu18172815