Ashwagandha
Evidence Fact Sheet
Withania somnifera
Ashwagandha (Withania somnifera) is an adaptogenic botanical extract studied for HPA-axis/cortisol modulation, with human RCTs and meta-analyses on stress, anxiety, sleep, strength, male fertility markers, cognition and thyroid. US DSHEA supplement (self-affirmed GRAS); banned as a food supplement in Brazil; not approved in China. Typical research dose 300-600 mg/day standardized root extract.
Also known as: Withania somnifera · Indian ginseng · Winter cherry · Withanolides · KSM-66 · Sensoril
Overview
Ashwagandha (Withania somnifera), known in Ayurveda as Indian ginseng, is a root-extract botanical whose withanolide triterpenoids are proposed to act via HPA-axis modulation (cortisol downregulation), GABA-A receptor positive modulation, and NF-κB-related anti-inflammatory signaling. It is most commonly studied as a standardized root extract (KSM-66 full-root, typically 300-600 mg/day; the root+leaf Sensoril line at 125-250 mg/day is a separate, non-interchangeable evidence stream), usually for 6-12 weeks. In the US it is sold under DSHEA as a dietary supplement (KSM-66 holds self-affirmed GRAS, which is not an FDA approval) limited to structure/function claims. Regulatory status differs sharply elsewhere: Brazil's ANVISA prohibits it as a food/supplement, it is not approved in China, and the EU permits food-supplement sale in some member states but authorizes no health claim and has flagged it for a Novel Food / hepatotoxicity review. A documented but unresolved drug-induced liver injury safety signal exists.
Mechanism of Action
HPA-axis modulation with downregulation of serum cortisol (chronic-stress RCTs report ~20-30% mean morning cortisol reduction) · GABA-A receptor positive modulation (proposed anxiolytic mechanism) · NF-κB / IKKβ inhibition reducing TNF-α / IL-6 / COX-2 inflammatory signaling (withaferin A, withanolide D) · Lipophilic free-radical scavenging / antioxidant activity of withanolide triterpenoids · Mild modulation of testosterone/LH and thyroid T3/T4 axes (small-RCT signal, not hormone replacement)
Body systems: Endocrine & Metabolic · Mood & Stress Response · Sleep-Wake System · Neurological & Cognitive · Musculoskeletal · Reproductive · Autonomic Nervous System
Evidence-Based Benefits
Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Ashwagandha is not characterized as a treatment for any disease.
Stress and Anxiety
Meta-analysis supported- SMD -1.75stress · p=.005
- SMD -1.55anxiety · p=.005
- 12 RCTs · 1,002pooled participants
A meta-analysis of randomized controlled trials found ashwagandha supplementation was associated with significantly lower self-reported stress and anxiety versus placebo. The authors explicitly rated the certainty of evidence as low and noted very high statistical heterogeneity, so the pooled effect should be read as a research signal rather than a settled effect size.
Reported effect: Stress SMD -1.75 (95% CI -2.29 to -1.22; p=.005; I2=83.1%); anxiety SMD -1.55 (95% CI -2.37 to -0.74; p=.005; I2=93.8%); 12 RCTs, 1,002 participants
“Ashwagandha supplementation significantly reduced anxiety (SMD: -1.55, 95% CI: -2.37, -0.74; p = .005; I2 = 93.8%) ... stress level (SMD: -1.75; 95% CI: -2.29, -1.22; p = .005; I2 = 83.1%) compared to the placebo ... the certainty of the evidence was low for both outcomes”
Source: PMID 36017529 · Akhgarjand 2022 · Phytother Res
Serum Cortisol / Stress Markers
RCT supported- P=0.0006serum cortisol drop
- P<0.0001stress-scale scores
- 64 subjectschronic-stress adults
In a randomized, double-blind, placebo-controlled trial in adults with a chronic-stress history, a high-concentration full-spectrum root extract significantly reduced serum cortisol and scores on all stress-assessment scales at day 60 versus placebo. The abstract reports statistical significance (p-values) rather than a percent reduction, so no percentage figure is claimed here.
Reported effect: Serum cortisol reduced P=0.0006 vs placebo; stress-assessment scale scores reduced P<0.0001 at Day 60; n=64
“The serum cortisol levels were substantially reduced (P=0.0006) in the Ashwagandha group, relative to the placebo group. ... a significant reduction (P<0.0001) in scores on all the stress-assessment scales on Day 60, relative to the placebo group.”
Source: PMID 23439798 · Chandrasekhar 2012 · Indian J Psychol Med
Sleep Quality
Meta-analysis supported- SMD -0.59overall sleep
- 5 RCTs · 400pooled participants
- I2 = 62%heterogeneity
A systematic review and meta-analysis found ashwagandha extract had a small but statistically significant beneficial effect on overall sleep versus placebo, with more pronounced effects in the subgroups with an insomnia diagnosis, doses of 600 mg/day or higher, and treatment of 8 weeks or longer. Quality-of-life measures showed no significant benefit.
Reported effect: Overall sleep SMD -0.59 (95% CI -0.75 to -0.42; I2=62%); 5 RCTs, 400 participants
“Ashwagandha extract exhibited a small but significant effect on overall sleep (Standardized Mean Difference -0.59; 95% Confidence Interval -0.75 to -0.42; I2 = 62%).”
Source: PMID 34559859 · Cheah 2021 · PLoS One
Muscle Strength and Exercise
RCT supported- 46.0 vs 26.4 kgbench press · p=0.001
- 96.2 vs 18.0 ng/dLtestosterone · p=0.004
- 57 subjects8-week trial
In a randomized controlled trial of resistance-training men taking 300 mg root extract twice daily for 8 weeks, ashwagandha produced significantly larger gains in bench-press and leg-extension strength, arm muscle size and testosterone versus placebo. A broader Bayesian meta-analysis (Bonilla 2021) reported the same favorable direction for physical performance but did not provide an extractable pooled effect size in its abstract.
Reported effect: Bench press +46.0 vs +26.4 kg (p=0.001); leg extension +14.5 vs +9.8 kg (p=0.04); testosterone +96.2 vs +18.0 ng/dL (p=0.004); n=57, 8 weeks, 300 mg twice daily
“Placebo: 26.4 kg, 95% CI, 19.5, 33.3 vs. Ashwagandha: 46.0 kg, 95% CI 36.6, 55.5; p = 0.001 ... Testosterone Increase ... Placebo: 18.0 ng/dL, 95% CI, -15.8, 51.8 vs. Ashwagandha: 96.2 ng/dL, 95% CI, 54.7, 137.5; p = 0.004”
Source: PMID 26609282 · Wankhede 2015 · J Int Soc Sports Nutr
Male Reproductive / Semen Quality
RCT supported- 167%sperm count · P<0.0001
- 57%sperm motility · P<0.0001
- 46 malesoligospermic · 90 d
A pilot randomized controlled trial in oligospermic (low-sperm-count) men taking 675 mg/day root extract for 90 days reported large within-group increases in sperm count, semen volume and motility versus baseline. This is a small pilot study in a clinically selected fertility population, not a demonstration of general fertility enhancement in healthy men.
Reported effect: 167% increase in sperm count (P<0.0001); 53% increase in semen volume (P<0.0001); 57% increase in sperm motility (P<0.0001); 46 oligospermic males, 675 mg/day, 90 days
“167% increase in sperm count (9.59 ± 4.37 × 10(6)/mL to 25.61 ± 8.6 × 10(6)/mL; P < 0.0001) ... 53% increase in semen volume ... 57% increase in sperm motility (18.62 ± 6.11% to 29.19 ± 6.31%; P < 0.0001)”
Source: PMID 24371462 · Ambiye 2013 · Evid Based Complement Alternat Med
Cognition and Memory
RCT supported- p = 0.007logical memory I
- p = 0.002Eriksen Flanker task
- 50 adultsmild cognitive impairment
In a randomized controlled trial of 50 adults with mild cognitive impairment taking 300 mg root extract twice daily for 8 weeks, the ashwagandha group showed significantly greater improvement in immediate and general memory and in executive-function/processing-speed tasks versus placebo. Results are from a single small trial in a selected population.
Reported effect: Logical memory I (p=0.007), logical memory II (p=0.006); Eriksen Flanker task (p=0.002), Trail-Making test A (p=0.006); 50 adults, 300 mg twice daily, 8 weeks
“logical memory I (p = 0.007) ... logical memory II (p = 0.006) ... Eriksen Flanker task (p = 0.002) ... Trail-Making test part A (p = 0.006)”
Source: PMID 28471731 · Choudhary 2017 · J Diet Suppl
Thyroid Markers (Subclinical Hypothyroid)
RCT supported- p < 0.001serum TSH
- p = 0.0031T3 · p=0.0096 T4
- 50 randomized8-week trial
In a double-blind, placebo-controlled trial in subclinical-hypothyroid patients, 8 weeks of ashwagandha significantly improved serum TSH, T3 and T4 versus placebo. This thyroid-stimulating signal also underlies the caution that ashwagandha may be inappropriate for people with hyperthyroidism or on thyroid medication.
Reported effect: Serum TSH improved p<0.001; T3 p=0.0031; T4 p=0.0096 vs placebo; 50 randomized (46 analyzed), 8 weeks
“Eight weeks of treatment with ashwagandha improved serum TSH (p < 0.001) ... improved ... T3 (p = 0.0031), and T4 (p = 0.0096) levels significantly compared to placebo.”
Source: PMID 28829155 · Sharma 2018 · J Altern Complement Med
Hormones and Vitality in Aging Males (Honest Negative)
Null / no benefit RCT supported- 14.7%testosterone · p=.010
- 43 completed16-wk crossover
A randomized, double-blind, placebo-controlled crossover trial in aging, overweight males found ashwagandha was associated with greater increases in testosterone and DHEA-S, but reported NO significant between-group differences in cortisol and NO significant between-group differences in self-reported fatigue, vigor, or sexual and psychological well-being. This is an important honest negative: hormonal biomarkers moved while the subjective vitality outcomes did not separate from placebo.
Reported effect: Testosterone +14.7% (p=.010) and DHEA-S +18% (p=.005) vs placebo; no significant between-group difference in cortisol; no significant between-group difference in fatigue, vigor, or sexual/psychological well-being; 43 completers, 16-week crossover
“Ashwagandha intake was associated with...14.7% greater increase in testosterone (p = .010) ... an 18% greater increase in DHEA-S (p = .005) ... There were no significant between-group differences in cortisol ... Improvements in fatigue, vigor, and sexual and psychological well-being were reported over time, with no statistically significant between-group differences”
Source: PMID 30854916 · Lopresti 2019 · Am J Mens Health
Physical Performance (Review-Level)
Emerging / indexedA systematic review and Bayesian meta-analysis concluded ashwagandha was more efficacious than placebo for physical-performance variables (strength/power, cardiorespiratory fitness, fatigue/recovery) in healthy men and women. The abstract describes the direction of effect and notes more comparable studies are needed for stable estimates, but does not report an extractable single pooled effect size, so no numeric effect is claimed.
Effect size: this study reports the direction of the finding but does not state a specific numeric effect size, so none is given here rather than estimated.
“The meta-analytic approaches of the included studies revealed that Ashwagandha supplementation was more efficacious than placebo for improving variables related to physical performance in healthy men and female. ... future interventions might be at least in some way beneficial on the analyzed outcomes”
Source: PMID 33670194 · Bonilla 2021 · J Funct Morphol Kinesiol
Dosage (research context · not a recommendation)
300-600 mg/day standardized root extract (KSM-66 full-root ≥5% withanolides · 6-8 wk for stress/sleep, 8-12 wk for exercise/male markers; Sensoril root+leaf ≥10% at 125-250 mg/day is a separate, non-interchangeable evidence line) — educational reference, not a dosing recommendation
Regulatory Status · 4 Markets
- US · FDA
- DSHEA dietary supplement; KSM-66 holds self-affirmed GRAS (sponsor panel, NOT an FDA no-questions GRN letter, so FDA approved is never accurate); structure/function claims only with mandatory disclaimer; FDA warning letters issued against disease claims
- EU · EFSA
- Marketable as a food supplement in several member states (recognized traditional food-use history, not Novel Food) but NO authorized Art.13/14 health claim; 2024 EU Heads of Food Safety Agencies recommended an Article 8 Novel Food assessment over hepatotoxicity / reproductive / thyroid concerns; member-state policies differ
- CN · China
- Not approved in China: absent from SAMR health-food positive list, novel-food approvals, and medicine-food homology list; not permitted in common food. Only gray cross-border e-commerce; no functional claims.
- BR · ANVISA
- Prohibited as food / food supplement (ANVISA RE no 3.669/2022 bans commercialization, import, advertising and use of Withania somnifera); exception: individualized pharmacy compounding under RDC 67/2007 with a qualified prescription
Safety
Generally well tolerated in 6-8 wk RCTs (AE rate ~placebo, mild GI upset <5%). Rare hepatotoxicity (DILI) case signals: Iceland MAST 2023, Netherlands Lareb 2024, Björnsson 2020 DILIN case series (PMID 31991029) — causality not fully established but a documented safety signal (avoid 100% safe framing). Contraindicated in pregnancy / trying-to-conceive / lactation and in hyperthyroidism / Graves disease; caution with sedatives, thyroid, immunosuppressant medication and hormone-dependent prostate cancer. Not for under-18.
Related
Goals: cognitive-support · longevity-stack
Lifestyles: high-stress · athletic-performance
References
PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.
- PMID 36017529 · Akhgarjand 2022 · Phytother Res — Stress and Anxiety
- PMID 23439798 · Chandrasekhar 2012 · Indian J Psychol Med — Serum Cortisol / Stress Markers
- PMID 34559859 · Cheah 2021 · PLoS One — Sleep Quality
- PMID 26609282 · Wankhede 2015 · J Int Soc Sports Nutr — Muscle Strength and Exercise
- PMID 24371462 · Ambiye 2013 · Evid Based Complement Alternat Med — Male Reproductive / Semen Quality
- PMID 28471731 · Choudhary 2017 · J Diet Suppl — Cognition and Memory
- PMID 28829155 · Sharma 2018 · J Altern Complement Med — Thyroid Markers (Subclinical Hypothyroid)
- PMID 30854916 · Lopresti 2019 · Am J Mens Health — Hormones and Vitality in Aging Males (Honest Negative)
- PMID 33670194 · Bonilla 2021 · J Funct Morphol Kinesiol — Physical Performance (Review-Level)
Frequently Asked Questions
1. What is the strongest evidence for ashwagandha?
The best-pooled human evidence is for stress and anxiety, where a meta-analysis of 12 RCTs (1,002 participants) reported significantly lower stress (SMD -1.75) and anxiety (SMD -1.55) versus placebo, and for sleep, where a meta-analysis of 5 RCTs (400 participants) found a small but significant effect on overall sleep (SMD -0.59). Both meta-analyses flagged limitations — low certainty of evidence and high heterogeneity for stress/anxiety — so these are research signals, not proof of a fixed effect.
2. Does ashwagandha actually lower cortisol?
A randomized, double-blind, placebo-controlled trial in 64 chronically stressed adults found serum cortisol was significantly reduced versus placebo (P=0.0006), alongside significant drops in stress-scale scores (P<0.0001). Notably, this is not universal: a separate crossover trial in aging overweight males found no significant between-group difference in cortisol, so the cortisol effect appears to depend on the population studied.
3. What are the honest negatives for ashwagandha?
In the crossover trial in aging, overweight males (Lopresti 2019), even though testosterone rose 14.7% (p=.010), there were no significant between-group differences in cortisol and no significant between-group differences in self-reported fatigue, vigor, or sexual and psychological well-being. The sleep meta-analysis also found no significant benefit on quality-of-life measures, and the stress/anxiety meta-analysis rated its evidence certainty as low with very high heterogeneity.
4. What dose was used in the research?
Most stress, sleep, strength and cognition trials used a standardized root extract at 300-600 mg/day (commonly 300 mg twice daily), typically for 6-12 weeks; the male-fertility pilot used 675 mg/day for 90 days. The root+leaf Sensoril line is dosed differently (125-250 mg/day) and is a separate, non-interchangeable evidence stream. These are descriptions of what studies used, not a dosing recommendation.
5. Is ashwagandha legal and approved where I live?
It varies sharply by region. In the US it is a DSHEA dietary supplement (the KSM-66 extract holds self-affirmed GRAS, which is not an FDA approval) limited to structure/function claims. In the EU it can be sold as a food supplement in some member states but carries no authorized health claim and has been flagged for a Novel Food / safety review. Brazil's ANVISA prohibits it as a food or food supplement, and it is not approved for food use in China.
Last evidence review: 2026-06-13