Current evidence suggests modest improvements, but the benefits are smaller and less certain than supplement marketing claims.

Key Points

Four meta-analyses show small-to-moderate improvements in strength and VO2max from ashwagandha supplementation, but the majority of included studies used untrained subjects where any stimulus produces exaggerated gains.
Cortisol reduction of 22-28% is the most consistent and well-replicated finding across multiple independent trials.
Testosterone effects are modest and appear mainly in chronically stressed or older individuals - not in healthy, well-trained young men already at normal hormonal baselines.
Sleep quality improvement may be the most practically relevant benefit for serious trainees, since sleep is the single most important recovery variable you control.
Most ashwagandha performance studies have 40-60 participants, are funded by extract manufacturers, and have not been replicated in well-trained populations. Treat the headline numbers with appropriate skepticism.

Introduction

Ashwagandha has gone from an obscure Ayurvedic herb to one of the best-selling supplements in America over the last five years. If your Instagram is like mine, your feed has at least three ads for it everytime you scroll. Every "natural testosterone booster" formula lists it as a lead ingredient, and podcasters mention it between mattress sponsors.

The marketing claims range from plausible to absurd: reduced stress, better sleep, increased testosterone, more muscle, improved endurance, enhanced recovery. Some of these have research behind them. Some are extrapolations from rodent studies. Most supplement companies do not bother distinguishing between the two.

Here is what I wanted to know when clients started asking about it: does ashwagandha actually improve training outcomes in people who already train seriously? Not in sedentary college students doing their first 8-week resistance program. Not in stressed office workers. In people who are already doing the hard work…does this move the needle?

The answer is more nuanced than the supplement industry wants you to believe, and more interesting than the blanket dismissals suggest. There is real science here, but there are also real limitations that don’t get talked about as much. Let's walk through all of it.

What Is Ashwagandha?

Withania somnifera ( commonly known as ashwagandha) is a plant in the nightshade family native to India, the Middle East, and parts of Africa. It has been used in Ayurvedic medicine for over 3,000 years, traditionally classified as a "rasayana" (rejuvenating tonic). The name literally means "smell of the horse," referring both to the root's smell and the traditional belief that it confers the strength of a horse.

The active compounds are withanolides, a group of steroidal lactones that modulate the hypothalamic-pituitary-adrenal (HPA) axis, GABA receptors, and various inflammatory pathways. Not all ashwagandha is the same. The withanolide content varies dramatically depending on the plant part used (root vs. leaf), extraction method, and standardization process. This is a critical point that most articles gloss over. There are three common formulations, and they are not interchangeable:

Extract	Plant Part	Withanolide Standardization	Typical Dose	Research Volume
KSM-66	Root only	≥5% withanolides	300 mg twice daily (600 mg/day)	High — majority of RCTs
Sensoril	Root + leaf	≥10% withanolide glycosides	125-500 mg/day	Moderate
Generic root extract	Varies	Unstandardized or variable	500 mg twice daily	Low (older studies)

When you see a study on "ashwagandha," the first question should always be: which extract, at what dose, standardized to what withanolide concentration? A finding with 600 mg/day KSM-66 does not automatically apply to the 300 mg generic root powder in your cabinet.

Strength and Muscle: What the RCTs Show

Perhaps the biggest reason people are interested in ashwagandha is for muscle and strength. So let's start there. The two most-cited RCTs tell somewhat different stories.

Wankhede et al. (2015) is the study that launched ashwagandha into the fitness mainstream. Fifty-seven young men with "limited resistance training experience" took either 600 mg/day KSM-66 or placebo for 8 weeks while following a supervised resistance training program. The ashwagandha group gained significantly more bench press strength, leg extension strength, arm circumference, and had a greater reduction in body fat percentage and exercise-induced muscle damage.

The numbers were striking: the ashwagandha group roughly doubled the placebo group's bench press gains. That is an extraordinary effect size for any single-ingredient supplement, and it should raise your eyebrows. The subjects were untrained, which means they were in the steepest part of their strength curve where literally everything works better. And the study was funded in part by Ixoreal Biomed, the company that manufactures KSM-66.

Ziegenfuss et al. (2018) provides a useful counterpoint. Forty-three recreationally active men took 500 mg/day Sensoril or placebo for 12 weeks with resistance training. The ashwagandha group showed significantly greater squat 1RM improvements and better perceived recovery, but bench press gains did not reach statistical significance, and there were no significant differences in body composition or testosterone.

The most recent meta-analysis (Doma et al., 2023) pooled 13 RCTs and found significant pooled effects for both upper and lower body strength, with small-to-moderate effect sizes. The subgroup analysis is telling: benefits appeared in both trained and untrained populations, but effect sizes were notably larger in untrained subjects.

Study	n	Population	Extract / Dose	Duration	Key Strength Findings
Wankhede et al. (2015)	57	Untrained males	KSM-66, 600 mg/day	8 weeks	Bench +46 kg vs +26 kg placebo; leg ext significant
Ziegenfuss et al. (2018)	43	Recreationally active males	Sensoril, 500 mg/day	12 weeks	Squat significant; bench NS; no body comp changes
Sandhu et al. (2010)	40	Healthy young adults	Generic root, 1000 mg/day	8 weeks	Improved velocity and power (Wingate)
Choudhary et al. (2015)	50	Athletic adults	KSM-66, 600 mg/day	12 weeks	Improved VO2max and time to exhaustion

The honest summary is that ashwagandha probably provides a small strength benefit when combined with resistance training, but the magnitude is likely much smaller than the Wankhede headline numbers suggest, especially if you already have meaningful training experience. If you have been lifting for three or more years, expect underwhelming results compared to what the studies in beginners show.

Cardiorespiratory Endurance

Surprisingly, the VO2max data is one of the more consistent findings in the ashwagandha literature. Perez-Gomez et al. (2020) conducted a meta-analysis of 5 studies focused specifically on cardiorespiratory fitness and found a statistically significant improvement in VO2max in both athletic and non-athletic populations. Choudhary et al. (2015) showed improved VO2max and time to exhaustion over 12 weeks in athletic adults using 600 mg/day KSM-66. Shenoy et al. (2012) found similar VO2max improvements in young athletic adults over 8 weeks.

Bonilla et al. (2021) reported a pooled standardized mean difference of approximately 1.2 for VO2max in their Bayesian meta-analysis. That is a large effect size…implausibly large for a herbal supplement. For context, a structured endurance training program typically produces an SMD of 0.5-0.8 for VO2max. A supplement producing a larger effect than the training itself should trigger skepticism, not excitement.

There are a few plausible explanations: the included studies had small samples (amplifying noise), several used populations with low baseline fitness (more room for improvement), and the heterogeneity across studies was moderate. The VO2max benefit is probably real but substantially smaller than the pooled numbers suggest.

The Cortisol Connection

If there is one area where ashwagandha has a genuinely strong evidence base, it is cortisol reduction. This is consistent, replicated across multiple independent trials, and mechanistically well-understood through the withanolides' modulation of the HPA axis.

Chandrasekhar et al. (2012) gave 64 adults with chronic stress 300 mg KSM-66 twice daily for 60 days and measured a 27.9% reduction in serum cortisol compared to placebo. Salve et al. (2019) tested both 250 mg and 600 mg doses in 58 adults over 8 weeks, finding significant cortisol reductions at both doses, with the higher dose producing a ~22% reduction.

This matters more than it sounds. Chronically elevated cortisol is catabolic, it impairs muscle protein synthesis, disrupts sleep architecture, increases fat storage (particularly visceral), and delays recovery between sessions. If you are someone who trains hard while managing a stressful job, poor sleep, or general life chaos, cortisol is likely a meaningful bottleneck in your recovery capacity.

If your training bottleneck is recovery and stress management (not training intensity or volume) this is where ashwagandha has its strongest case. The cortisol reduction is real, replicated, and mechanistically coherent. But this benefit is about removing a brake, not pressing a gas pedal. It will not make you stronger by itself…it may help you recover better from the training that does.

This framing also explains why studies in untrained subjects show larger effects. Beginners are typically more stressed by training (higher relative cortisol response) and less efficient at recovery. A cortisol-lowering supplement has more room to help when cortisol is elevated to begin with.

Testosterone: Separating Signal from Noise

This is the claim that sells the most bottles and has the weakest evidence in the population that is buying them.

Wankhede et al. (2015) reported a significant testosterone increase in their ashwagandha group (roughly 15% above baseline more than placebo). This finding has been amplified across every supplement marketing channel on the internet. What is mentioned less often: the subjects were untrained young men doing resistance training for the first time, resistance training itself increases testosterone, and the study was manufacturer-funded.

Ziegenfuss et al. (2018) found no significant testosterone changes with Sensoril extract. Lopresti et al. (2019) found a ~14.7% increase in overweight men using KSM-66 for 16 weeks — but this was not an exercise study, and it was also funded by Ixoreal Biomed.

Chauhan et al. (2022) conducted a systematic review of ashwagandha and testosterone and concluded that effects are modest and inconsistent. The testosterone benefit appears most reliably in individuals with elevated stress, suboptimal baseline testosterone, or age-related decline, not in healthy, eugonadal, well-trained young men.

Study	Population	Testosterone Finding	Funding
Wankhede et al. (2015)	Untrained young males	Significant increase (~15% vs placebo)	Ixoreal Biomed (KSM-66)
Ziegenfuss et al. (2018)	Recreationally active males	No significant change	Natreon (Sensoril)
Lopresti et al. (2019)	Overweight males (non-exercise)	~14.7% increase vs placebo	Ixoreal Biomed (KSM-66)
Chauhan et al. (2022)	Systematic review	Modest, inconsistent; strongest in stressed/older	N/A (review)

The bottom line: if you are a healthy man in your 20s or 30s with normal testosterone levels, do not take ashwagandha expecting a meaningful hormonal shift. If you are chronically stressed, sleep-deprived, or over 40 with suboptimal levels, there is a plausible (but not conclusive) case that it may help normalize, not supercharge, your testosterone. This is a long way from most of the claims of "natural testosterone booster" marketing.

Sleep and Recovery

This might be the most underrated angle of the ashwagandha story, and the one most relevant to serious trainees.

Langade et al. (2019) gave 150 adults 600 mg/day KSM-66 for 6 weeks and found significant improvements in sleep quality (Pittsburgh Sleep Quality Index), sleep onset latency, and total sleep time. Deshpande et al. (2020) found similar results with 600 mg/day over 8 weeks in 80 healthy adults. It improved overall sleep quality, reduced non-restorative sleep, and better subjective sleep efficiency.

Sleep is not a minor variable. It is the single most powerful recovery tool you have. A 2021 review in Sports Medicine found that even modest sleep restriction (6 vs. 8 hours) significantly impairs next-day strength performance, reduces testosterone, increases cortisol, and compromises muscle protein synthesis. If ashwagandha meaningfully improves sleep quality, even modestly, the downstream effects on training recovery could be more impactful than any direct performance mechanism.

This is where I think ashwagandha connects to what we track at Verro. If you are going to invest in a supplement, do not rely on how you "feel." Track session-to-session e1RM trends. Compare InBody segmental lean mass across 6-12 week windows. Monitor your rate of perceived recovery between sessions. If ashwagandha is working for you, those numbers should reflect it. If they do not, you have your answer, regardless of what the studies say about group averages.

What the Evidence Doesn't Support

An honest accounting of the limitations is the most important section in this article, and the one you will not find on the supplement company's website.

Small samples. The typical ashwagandha performance study has 40-60 total participants. This is statistically underpowered for detecting small-to-moderate effects reliably. Noise looks like signal in small studies, which is one reason effect sizes in this literature look so large.

Industry funding. Ixoreal Biomed, the manufacturer of KSM-66, funded or supplied product for the majority of the most-cited positive studies: including Wankhede (2015), Choudhary (2015), Lopresti (2019), Langade (2019), and Chandrasekhar (2012). Natreon, the Sensoril manufacturer, supplied Ziegenfuss (2018). This does not invalidate the results, but it is a significant bias concern that deserves transparency. Independent replication from non-industry-funded Western research labs is limited.

Population mismatch. The vast majority of exercise performance studies used untrained or recreationally active males. If you have been training consistently for years, you are not the population these studies describe. Novice gains exaggerate the apparent effect of any supplement (or any training program, for that matter). Female-specific data is severely lacking.

Geographic concentration. A disproportionate number of studies come from Indian institutions, where ashwagandha has deep cultural significance. This does not mean the research is invalid, but independent replication from diverse research groups strengthens confidence, and that replication has been slow to materialize.

Regulatory skepticism. In 2023, the European Food Safety Authority (EFSA) declined to approve health claims for ashwagandha, citing insufficient evidence quality and a signal of potential hepatotoxicity. Several case reports of liver injury have been documented internationally. The risk is rare but real and worth knowing about.

Publication bias. Null results in supplement research are less likely to be published. The literature almost certainly overrepresents positive findings. We are seeing the highlight reel, not the full game tape.

Dosing, Safety, and Practical Considerations

If you do decide to try ashwagandha (with realistic expectations) here is what the research supports on practical implementation.

Dose: 600 mg/day of KSM-66 (300 mg twice daily) is the best-studied protocol and should be the default choice. Sensoril at 250-500 mg/day is an alternative with moderate research support. Generic root extracts are harder to dose reliably due to variable withanolide content.

Duration: Most studies showing significant results ran 8-12 weeks. Do not expect meaningful effects before 4 weeks. There is no long-term data beyond 16 weeks.

Timing: No strong evidence for optimal timing. Most studies used split dosing (morning and evening) with meals. Taking it with food may reduce the mild GI discomfort some people experience.

Safety concerns:

GI discomfort — nausea, diarrhea, and stomach upset are the most common side effects, usually mild and transient
Hepatotoxicity — rare but documented case reports of liver injury; EFSA flagged this in 2023
Thyroid stimulation — ashwagandha can increase thyroid hormone production, making it contraindicated for hyperthyroidism and requiring caution with thyroid medications
Drug interactions — may interact with immunosuppressants, sedatives, thyroid medications, and blood sugar-lowering drugs
Pregnancy — contraindicated

Cycling: No strong evidence for or against cycling. Some practitioners recommend 8-12 weeks on, 2-4 weeks off, but this is convention rather than evidence-based protocol. Given the lack of long-term safety data, periodic breaks seem reasonable.

Practical Takeaways

Set realistic expectations. Ashwagandha is not a game-changer for experienced lifters. It is a modest recovery support tool at best, and the magnitude of benefit decreases the more trained you already are.
Prioritize sleep and stress management first. If you sleep 5 hours a night and are chronically stressed, ashwagandha is a bandage on a structural problem. Fix the foundations before optimizing the margins.
Choose a standardized extract. KSM-66 at 600 mg/day has the most research behind it. Generic root powders have variable potency and less supporting evidence.
Run an 8-12 week self-experiment with data. Track e1RM trends, InBody scans, and session recovery scores before, during, and after supplementation. If the numbers do not move, save your money.
Be skeptical of testosterone claims. Unless you are chronically stressed, sleep-deprived, or over 40 with suboptimal levels, do not expect meaningful hormonal changes from ashwagandha.
Talk to your doctor first. This is especially important if you take thyroid medications, immunosuppressants, sedatives, or have liver concerns. The rare hepatotoxicity signal is worth a conversation.
Do not stack ashwagandha with every other "adaptogen" on the shelf. Combining multiple supplements with overlapping mechanisms makes it impossible to attribute any benefit (or side effect) to the right source.

References

Citation (APA)	Study Type	Why It Matters	Supports This Claim
Bonilla, D.A., et al. (2021). Effects of Ashwagandha (Withania somnifera) on Physical Performance: Systematic Review and Bayesian Meta-Analysis. Journal of Functional Morphology and Kinesiology, 6(1), 20.	Systematic review / meta-analysis	Pools the RCT evidence on physical performance using Bayesian methods	Ashwagandha has small favorable effects on strength and power
Doma, K., et al. (2023). The effect of ashwagandha supplementation on physical performance: A systematic review and meta-analysis. Journal of the International Society of Sports Nutrition, 20(1), 2243113.	Meta-analysis (13 RCTs)	Most recent pooled analysis, with subgroup analysis by training status	Effects are real but notably larger in untrained subjects
Wankhede, S., et al. (2015). Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial. Journal of the International Society of Sports Nutrition, 12, 43.	RCT	The headline study that launched ashwagandha into the fitness mainstream	Large strength/fat-loss gains — but in untrained, manufacturer-funded subjects
Ziegenfuss, T.N., et al. (2018). Effects of an aqueous extract of Withania somnifera on strength training adaptations and recovery: The STAR trial. Nutrients, 10(11), 1807.	RCT	Tested resistance-trained men with a controlled design	Squat improved; bench NS; no body-comp or testosterone change
Pérez-Gómez, J., et al. (2020). Effects of Ashwagandha (Withania somnifera) on VO2max: A Systematic Review and Meta-Analysis. Nutrients, 12(4), 1119.	Meta-analysis	Pools VO2max outcomes across trials	Ashwagandha improves VO2max
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 in reducing stress and anxiety in adults. Indian Journal of Psychological Medicine, 34(3), 255-262.	RCT	Established the cortisol-reduction effect	Cortisol drops ~28% — the most consistent finding
Salve, J., et al. (2019). Adaptogenic and anxiolytic effects of ashwagandha root extract in healthy adults: A double-blind, randomized, placebo-controlled clinical study. Cureus, 11(12), e6466.	RCT	Independently replicates the cortisol/stress effect	The cortisol reduction is well-replicated
Langade, D., et al. (2019). Efficacy and safety of ashwagandha (Withania somnifera) root extract in insomnia and anxiety: A double-blind, randomized, placebo-controlled study. Cureus, 11(9), e5797.	RCT	Tests sleep outcomes directly	Improves sleep quality — the key recovery variable for trainees
Lopresti, A.L., Drummond, P.D., & Smith, S.J. (2019). A randomized, double-blind, placebo-controlled, crossover study examining the hormonal and vitality effects of ashwagandha (Withania somnifera) in aging, overweight males. American Journal of Men's Health, 13(2), 1557988319835985.	RCT (crossover)	Tests testosterone/DHEA in aging, stressed men	Testosterone effects appear mainly in stressed/older men
Chauhan, S., et al. (2022). Effect of standardized root extract of ashwagandha (Withania somnifera) on well-being and sexual performance in adult males: A randomized controlled trial. Health Science Reports, 5(4), e741.	RCT	Tests well-being and sexual-performance outcomes	Hormonal/well-being effects are modest
Choudhary, B., Shetty, A., & Langade, D.G. (2015). Efficacy of ashwagandha (Withania somnifera [L.] Dunal) in improving cardiorespiratory endurance in healthy athletic adults. AYU, 36(1), 63-68.	RCT	Tests endurance in trained, athletic adults	Improves VO2max and time to exhaustion
Shenoy, S., Chaskar, U., Sandhu, J.S., & Paadhi, M.M. (2012). Effects of eight-week supplementation of ashwagandha on cardiorespiratory endurance in elite Indian cyclists. Journal of Ayurveda and Integrative Medicine, 3(4), 209-214.	RCT	Tests elite endurance athletes	Improves VO2max in trained cyclists

DISCLAIMER

Individual responses to supplementation vary considerably. What produces a measurable benefit for one person may do nothing for another, and the research does not yet allow us to predict who will respond. If you are considering ashwagandha supplementation, consult a qualified healthcare professional — particularly if you have thyroid conditions, liver concerns, take prescription medications, or are pregnant or nursing.

At Verro, we view supplementation as one small piece of a much larger training picture — not as a shortcut or substitute for the fundamentals of progressive training, adequate nutrition, quality sleep, and intelligent program design. The biggest performance gains for most people will always come from those foundations, not from what is in the bottle.

This article is for educational purposes only and is not intended to diagnose, treat, or serve as medical advice regarding peptide use, hormone optimization, or any related therapeutic intervention. The compounds discussed in this article include both FDA-approved medications and unapproved research chemicals — their inclusion here does not constitute an endorsement or recommendation for use.