- Several small randomized controlled trials suggest ashwagandha modestly improves muscle strength and recovery compared with placebo, but the overall evidence base is limited in size and quality.
- The most studied dose is 300–600 mg of a root extract (KSM-66 or Sensoril) taken daily for 8–12 weeks alongside resistance training.
- Effect sizes are real but modest — ashwagandha is not a replacement for progressive overload, adequate protein, or sleep.
- People with thyroid conditions, hormone-sensitive cancers, or who are pregnant should avoid it without medical clearance.
What the evidence shows
The honest answer is: there is a plausible signal, but the evidence is thin enough that you should temper expectations. Here is what the trials actually show.
The most-cited study is a double-blind RCT by Wankhede et al. (2015), which enrolled 57 young men performing resistance training. The group receiving 300 mg of KSM-66 ashwagandha twice daily for eight weeks showed significantly greater gains in bench-press and leg-extension one-rep-max compared with placebo, along with larger increases in muscle size and greater reductions in exercise-induced muscle damage (as measured by serum creatine kinase). The differences were statistically significant, but the sample was small and all participants were already lifting.
A second placebo-controlled trial by Ziegenfuss et al. (2018) tested Sensoril ashwagandha (500 mg/day) over 12 weeks in recreationally active adults. It found improvements in upper- and lower-body strength and a modest reduction in body fat percentage compared with placebo. Again, the sample was small (n=60).
A 2021 systematic review and meta-analysis by Pérez-Gómez et al. pooled data from five RCTs and concluded that ashwagandha supplementation produced small but statistically significant improvements in muscle strength and VO₂ max. The authors cautioned that most included trials had a high risk of bias due to small samples and industry involvement in some studies — a limitation worth taking seriously.
What the evidence does not show: no trial has demonstrated that ashwagandha produces strength gains in the absence of resistance training, no trial has run longer than 16 weeks, and no head-to-head comparison with creatine (the supplement with far stronger evidence for strength) exists. If you are not already training consistently, ashwagandha is unlikely to move the needle.
How it works (mechanism)
Ashwagandha (Withania somnifera) is classified as an adaptogen — a compound hypothesized to help the body manage physiological stress. Several plausible mechanisms have been proposed for its effect on strength, though none are definitively confirmed in humans:
- Cortisol modulation: Chronic elevation of cortisol is catabolic to muscle. Ashwagandha has been shown to reduce serum cortisol in stressed adults (Chandrasekhar et al., 2012), which could theoretically support a more anabolic environment during training.
- Testosterone: Some trials have observed modest increases in serum testosterone with ashwagandha supplementation (Wankhede et al., 2015; Ambiye et al., 2013), though the clinical significance of these changes remains debated.
- Reduced exercise-induced inflammation: Lower creatine kinase and inflammatory markers post-exercise may mean faster recovery and the ability to train harder over time (Wankhede et al., 2015).
These mechanisms are biologically plausible, but "plausible mechanism" is not the same as "proven effect." The human data are consistent with these pathways mattering, but confirmation requires larger, longer trials.
Dose & timing if you try it
If you decide the available evidence is sufficient for a personal trial, here is how the studied protocols were structured:
- Dose: 300–600 mg of a standardized root extract (look for KSM-66 or Sensoril on the label — these are the forms used in published research). Generic "ashwagandha powder" products are not standardized and have not been studied for this outcome.
- Timing: Most trials split the dose — one dose in the morning and one in the evening, with meals. There is no evidence that taking it immediately pre-workout confers additional benefit.
- Duration: Eight to twelve weeks is the minimum window used in trials showing an effect. Expect nothing meaningful in the first two to three weeks.
- Context: All positive trials involved participants following a structured resistance-training program. Supplement without training, and the data simply do not apply.
On cost and quality: third-party tested products (NSF Certified for Sport, Informed Sport, or USP verified) are preferable, especially for competitive athletes subject to doping controls, as ashwagandha supplements are not tightly regulated.
Who should skip it
- Pregnant individuals: Ashwagandha has been used traditionally as an abortifacient and animal studies raise uterotonic concerns. Avoid entirely during pregnancy (Jahanbakhsh et al., 2016).
- Breastfeeding individuals: Safety data are absent; skip until evidence exists.
- Thyroid conditions: Ashwagandha may increase thyroid hormone levels (Sharma et al., 2018). People on thyroid medications or with hyperthyroidism should consult their physician before use.
- Hormone-sensitive conditions: Because ashwagandha may influence testosterone and other hormones, people with hormone-sensitive prostate cancer or related conditions should avoid it without oncology input.
- Autoimmune disease: As a potential immune modulator, it is theoretically contraindicated in conditions like lupus, rheumatoid arthritis, or multiple sclerosis where immune stimulation could be harmful.
- Sedative medications: Ashwagandha has mild anxiolytic properties and may potentiate benzodiazepines or other CNS depressants.
- Liver disease: Rare case reports of hepatotoxicity linked to ashwagandha supplements have been published (Björnsson et al., 2020). People with pre-existing liver conditions should exercise caution.
Bottom line
Ashwagandha has a modest, real, but not overwhelming evidence base for supporting strength gains when used alongside consistent resistance training. It is not in the same tier as creatine monohydrate, which has decades of large-scale research behind it. If you are already covering the fundamentals — progressive training, sufficient protein (1.6–2.2 g/kg body weight), sleep, and recovery — and you want to trial a supplement with a plausible mechanism and an acceptable safety profile, a standardized extract at 300–600 mg/day for 8–12 weeks is a reasonable experiment. If you are looking for a shortcut around the fundamentals, no supplement qualifies.
References
- Ambiye, V.R., et al. (2013). Clinical evaluation of the spermatogenic activity of the root extract of Withania somnifera. Evidence-Based Complementary and Alternative Medicine.
- Björnsson, H.K., et al. (2020). Ashwagandha-induced liver injury: A case series from Iceland. Liver International, 40(4), 825–829.
- Chandrasekhar, K., Kapoor, J., & Anishetty, S. (2012). A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root. Indian Journal of Psychological Medicine, 34(3), 255–262.
- Jahanbakhsh, S.P., et al. (2016). Evaluation of the efficacy of Withania somnifera in patients with obsessive compulsive disorder. Complementary Therapies in Medicine, 27, 25–29.
- Pérez-Gómez, J., et al. (2021). Effects of ashwagandha (Withania somnifera) on VO₂max: A systematic review and meta-analysis. Nutrients, 13(4), 1119.
- Sharma, A.K., Basu, I., & Singh, S. (2018). Efficacy and safety of ashwagandha root extract in subclinical hypothyroid patients. Journal of Alternative and Complementary Medicine, 24(3), 243–248.
- Wankhede, S., et al. (2015). Examining the effect of Withania somnifera supplementation on muscle strength and recovery. Journal of the International Society of Sports Nutrition, 12, 43.
- Ziegenfuss, T.N., et al. (2018). Effects of an aqueous extract of Withania somnifera on strength training adaptations and recovery. Nutrients, 10(11), 1807.