Ashwagandha: What 500+ Studies Actually Show

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Ashwagandha (Withania somnifera) — specifically the KSM-66 root extract — reduces serum cortisol by 27.9% in chronically stressed adults across peer-reviewed RCTs. Shoden extract improves sleep onset latency and modestly raises testosterone in aging overweight men. Cognitive enhancement and libido claims do not replicate. A 2020 case series from Iceland and the U.S. Drug-Induced Liver Injury Network documented cholestatic liver injury with onset 2–12 weeks. Denmark banned ashwagandha from food supplements in 2023. The signal is real and form-specific. The risks are real and underreported.

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TL;DR — Ashwagandha by the receipts

• KSM-66 root extract, 300–600 mg/day: 27.9% cortisol reduction vs. placebo (Chandrasekhar et al, Indian J Psych Med 2012, n=64). 24+ industry-funded RCTs.
• Shoden extract, 120–240 mg/day: improves sleep onset latency and efficiency (Langade 2019, n=150). Raises testosterone 14.7% in aging overweight men only (Lopresti 2019, n=57).
• Cognition and libido claims do not replicate. The Alzheimer's Drug Discovery Foundation rates ashwagandha "limited" for cognitive benefit.
• Hepatotoxicity is documented. 5-case series, Iceland + US DILIN (Björnsson 2020). Cholestatic injury, onset 2–12 weeks. NIH LiverTox lists ashwagandha as a known hepatotoxic herb.
• Denmark banned ashwagandha from food supplements in 2023. Iceland's regulatory system flagged the liver cases in 2017–2018.
• Quality crisis: only 38% of products pass independent ConsumerLab testing.

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Ashwagandha is the most-searched supplement in the adaptogen category — roughly 1 million queries per month in English alone. The wellness industry has built a $1.5 billion global market on it. Amazon lists over 2,000 products containing it. Influencers call it the "stress destroyer," the testosterone booster, the cognitive enhancer, the sleep fix.

Here is the problem: almost every well-designed trial supporting those claims was funded by the company that manufactures the extract being tested. The lead researcher on the most-cited modern RCTs, Adrian Lopresti of Murdoch University in Australia, discloses his industry relationships in his papers — a fact his papers' conclusions are frequently cited without.

The signal is real. It is narrower than claimed. It is form-dependent. And there is a hepatotoxicity file that you will not find in the supplement aisle.

Why does KSM-66 dominate the ashwagandha evidence base?

When supplement brands cite "24 clinical trials," they are almost always citing trials on KSM-66 — a root-only extract manufactured by Ixoreal Biomed, an Indian ingredient company. Sensoril, manufactured by Natreon Inc., has 10+ trials of its own. A third extract, Shoden (produced by Arjuna Natural), is used in more recent studies. Generic ashwagandha root powder has a different alkaloid profile and substantially weaker evidence.

This matters more than most users understand. The active constituents in ashwagandha — withanolides, withanosides, and alkaloids — vary widely by plant part (root vs. leaf), extraction method (water vs. ethanol vs. supercritical CO₂), and standardization percentage. KSM-66 is standardized to ≥5% withanolides from root only. Shoden is standardized to 35% withanolide glycosides. Generic root powder may have 1–2% or none. A study showing effect on KSM-66 tells you almost nothing about the dollar-a-bottle product at your pharmacy.

The evidence base, in other words, is not for "ashwagandha." It is for specific proprietary extracts — extracts whose manufacturers have funded most of the supporting research.

"A high-concentration full-spectrum root extract significantly reduced scores on all stress-assessment scales relative to placebo (p < 0.0001)."

"All five studies reviewed concluded that ashwagandha intervention resulted in greater score improvements than placebo in anxiety or stress outcomes — while noting an assortment of study methods and potential bias."

What ashwagandha effects actually replicate in trials?

Three outcomes appear consistently across the best-designed trials. They are not marketing claims. They are peer-reviewed results with disclosed funding and measurable effect sizes.

Cortisol. Chandrasekhar et al. ran a 60-day randomized, double-blind, placebo-controlled trial (n=64) in chronically stressed adults. The ashwagandha group received 300 mg of KSM-66 twice daily. Serum cortisol dropped by 27.9% compared to placebo (p=0.0006). The PSS (Perceived Stress Scale) dropped 44% vs. 5.5% for placebo.

"Serum cortisol levels were substantially reduced in the ashwagandha group relative to the placebo group (p=0.0006)."

Lopresti et al. replicated the cortisol finding in 2019 using Shoden extract (240 mg/day, 60 days, n=60 stressed adults). Morning cortisol was significantly lower in the ashwagandha group vs. placebo (p < 0.001). The study was funded by Arjuna Natural Ltd, the Shoden manufacturer — and Lopresti says so in the paper's disclosures.

"Ashwagandha intake was associated with greater reductions in morning cortisol compared with placebo (p < .001). Arjuna Natural Ltd funded the project and supplied Shoden."

Anxiety. The 2019 Lopresti study also measured anxiety via the Hamilton Anxiety Rating Scale (HAM-A) and Depression, Anxiety, and Stress Scale-21 (DASS-21). HAM-A showed statistically significant reduction vs. placebo (p=0.040). The DASS-21 trended toward significance (p=0.096) but did not cross the threshold.

The Chandrasekhar 2012 trial showed significant improvements on every stress and anxiety scale measured. The effect exists. It is real. The honest reading of the evidence, however, is that ashwagandha produces moderate anxiety reduction in chronically stressed adults — not the elimination of anxiety disorder symptoms marketed in many product claims. The NCCIH, the U.S. National Center for Complementary and Integrative Health, reviewed the evidence in 2023 and concluded that evidence for insomnia and stress is supported, while "evidence is unclear about effects on anxiety."

"Research shows that some ashwagandha preparations may be effective for insomnia and stress. However, evidence is unclear about their effects on anxiety."

Sleep. Langade, Kanchi, Salve et al. ran a 10-week RCT (n=150) using Shoden standardized to 21 mg withanolide glycosides per 120 mg daily dose. The ashwagandha group showed significantly shorter sleep onset latency (29.0 min vs. 33.9 min for placebo, p < 0.019) and improved sleep efficiency (83.5% vs. 79.7%, p < 0.001). Non-restorative sleep — the subjective sense of waking unrefreshed — was also reduced significantly.

"Ashwagandha root extract significantly improved sleep quality, sleep onset latency, and sleep efficiency in adults with insomnia compared to placebo."

For adjacent evidence on sleep-supporting compounds, see our transmission on magnesium and sleep.

Athletic performance. Bonilla et al. published a Bayesian meta-analysis in 2021 (published in Sports, MDPI) covering multiple ashwagandha RCTs. Across 6 studies and 7 effect sizes for VO2 max, ashwagandha showed a statistically significant positive effect on cardiorespiratory fitness. The effect size was real but modest — meaningful for recreational athletes, not the performance revolution implied by sports supplement marketing.

"Ashwagandha supplementation over 8–24 weeks was associated with significant improvements in VO2 max and physical performance outcomes in a Bayesian meta-analysis of available RCTs."

Testosterone. Lopresti et al. ran a 16-week crossover RCT (n=57, overweight men aged 40–70, mild fatigue symptoms) using Shoden. Testosterone increased by 14.7% more than placebo (p=0.010). DHEA-S increased 18% more than placebo. Read that again: the testosterone finding requires a specific population (overweight, aging, mildly fatigued men), a specific extract (Shoden, 21 mg withanolide glycosides daily), and a 16-week duration. It does not generalize to young, lean, non-fatigued men.

"Ashwagandha was associated with a 14.7% greater increase in testosterone compared to placebo (p=.010) in aging, overweight males with mild fatigue symptoms."

Does ashwagandha actually improve cognition or libido?

The supplement industry's cognitive enhancement claims for ashwagandha draw primarily from one extract (Sensoril) and one research group. Pingali, Pilli, and Fatima ran a 6-month trial in 20 young healthy males. The ashwagandha group showed improvements in reaction time, digit vigilance, and memory tasks vs. placebo. The study was small. The population was young, healthy men — not the stressed, sleep-deprived adults who comprise most supplement buyers. Replication by independent groups is limited.

"Sensoril ashwagandha extract showed improvements in psychomotor and cognitive performance vs. placebo in a 6-month trial of 20 healthy male volunteers."

The Alzheimer's Drug Discovery Foundation's Cognitive Vitality program reviewed the evidence and rated ashwagandha as having "limited" evidence for cognitive benefit — one tier below "promising" — citing small study sizes and methodological limitations.

Claims around libido, sexual function, and male fertility draw from a small number of trials with serious methodological limitations, including lack of placebo controls and non-standardized extract use. The testosterone finding (above) is real — but testosterone modulation in a narrow clinical population is not the same as a universal aphrodisiac.

The distinction between a measurable, population-specific effect and a generalized health claim is exactly where supplement marketing routinely fails.

Which ashwagandha extract has the best evidence?

Extract	Primary claims supported	Funded RCT count	Largest study	Manufacturer-funded
KSM-66 (Ixoreal Biomed)	Cortisol, stress, anxiety	24+	Chandrasekhar 2012 (n=64)	Most trials
Sensoril (Natreon Inc.)	Cognition, stress	10+	Pingali 2014 (n=20)	Most trials
Shoden (Arjuna Natural)	Sleep, testosterone, cortisol	6+	Langade 2019 (n=150)	Most trials
Generic root powder	Unclear	Few	Not comparable	Varies

Read the table carefully: every extract's evidence base is dominated by manufacturer-funded studies. That does not mean the results are fabricated. It means independent replication — the standard by which science builds consensus — is thin.

For context on how structural funding conflicts shape research conclusions in wellness science, see our transmission on the Wim Hof Method, where independent replication confirmed core effects that were initially manufacturer-adjacent in origin.

Can ashwagandha cause liver damage?

In 2020, Björnsson et al. published a case series in Liver International — a peer-reviewed gastroenterology journal — documenting 5 cases of ashwagandha-induced liver injury. Three cases were collected in Iceland during 2017–2018. Two came from the U.S. Drug-Induced Liver Injury Network (DILIN).

The patients' mean age was 43 years (range: 21–62). All five developed jaundice 2 to 12 weeks after starting ashwagandha supplementation. Liver injury was cholestatic or mixed pattern. One biopsy showed acute cholestatic hepatitis. Pruritus and hyperbilirubinemia persisted for 5 to 20 weeks after stopping the supplement. No patient developed liver failure. Liver tests normalized in 1 to 5 months.

"Five cases of liver injury attributed to ashwagandha-containing supplements were identified — three in Iceland and two from DILIN. All patients developed jaundice 2–12 weeks post-initiation. Liver injury was cholestatic or mixed with prolonged pruritus and hyperbilirubinemia."

In April 2023, Denmark became the first European nation to formally ban ashwagandha from food supplements. The Danish Veterinary and Food Administration cited a 2020 risk assessment by the Technical University of Denmark raising concerns about hormonal disruption and potential reproductive effects at physiological doses. The ban's scientific basis has been contested by independent researchers — particularly the abortion risk claim, for which critics say clinical evidence is absent. But the liver injury finding is harder to dismiss.

The NIH's LiverTox database, which tracks drug-induced liver injury, lists ashwagandha as a known hepatotoxic herb with documented cases of clinically apparent liver injury, predominantly cholestatic in pattern.

"Ashwagandha has been implicated in rare instances of clinically apparent liver injury, which is typically cholestatic or mixed in pattern."

The incidence is low relative to usage — millions of people take ashwagandha without incident. But "low incidence" applied to a 1-million-monthly-search supplement means thousands of people per year may be at risk, and most will not associate their unexplained jaundice with the "stress supplement" they started a month earlier.

Plain statement: If you develop fatigue, dark urine, yellowing of the skin or eyes, or upper-right abdominal discomfort while using ashwagandha, stop immediately and consult a physician. This is a known, documented adverse event pattern, not a theoretical risk.

How many ashwagandha supplements pass quality testing?

The above evidence — all of it — applies to specific standardized extracts used in clinical trials. It does not apply to generic products with unverified alkaloid content.

ConsumerLab.com, an independent supplement testing organization, found that only 38% of ashwagandha products it reviewed passed testing for quality, accurate labeling, and contamination limits. Ashwagandha root powder has documented potential for heavy metal bioaccumulation — a 2010 review of medicinal plants found ashwagandha showing "very high metal bioaccumulation" relative to other plants examined.

"Only 38% of ashwagandha products reviewed by ConsumerLab.com passed testing for quality, label accuracy, and contamination limits."

Third-party certification from NSF International, USP, or ConsumerLab is the minimum floor for any product used beyond occasional, casual intake. Even then: the tested product is KSM-66, Sensoril, or Shoden — not the generic version with the same label claim.

For comparison on how quality control failures undercut even well-evidenced supplements, see our transmission on natural approaches to anxiety.

What we can say. What we can't.

We can say: KSM-66 root extract at 300–600 mg/day for 8–12 weeks reduces serum cortisol by approximately 27.9% relative to placebo in chronically stressed adults, based on a peer-reviewed RCT published in an indexed journal with disclosed industry funding.

We can say: Shoden extract at 120–240 mg/day improves sleep onset latency, sleep efficiency, and non-restorative sleep in adults with insomnia, based on a 10-week, 150-person RCT.

We can say: Shoden extract at 21 mg withanolide glycosides daily increases testosterone by approximately 14.7% more than placebo in overweight, aging men with mild fatigue — a specific population, a specific product, a specific duration.

We can say: cholestatic liver injury is a documented adverse event, captured in peer-reviewed case series from Iceland and the U.S. DILIN, with onset 2–12 weeks post-initiation.

We can't say: that "ashwagandha" as a category reliably produces any of these effects — extract, dose, and population all determine whether an effect exists.

We can't say: that cognitive enhancement claims for healthy young adults are well-supported. The evidence is preliminary, from small trials, in narrow populations.

We can't say: that long-term safety beyond 12 weeks is established. The longest well-designed trial runs 16 weeks. The Danish Technical University flagged hormonal concerns at chronic doses. The liver injury cases include durations as short as 2 weeks.

We can't say: what happens when an individual's product doesn't match the extract tested in the trial — which, given ConsumerLab's 38% pass rate, is more likely than not.

The supplement industry has built an enormous market on a real but narrow signal — then extrapolated it into a category, a lifestyle, an identity. The honest read of 500+ studies on ashwagandha is not "it works." It is: for specific extracts, at specific doses, in specific populations, it produces measurable effects on cortisol and sleep. The evidence for liver toxicity is real. The evidence for most marketing claims is not.

The question worth sitting with: if a pharmaceutical compound had a hepatotoxicity case series, an uncertain long-term safety profile, and a 38% product quality pass rate — would we treat the marketing claims with the same latitude we give to supplements?

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FAQ

What is the best form of ashwagandha?

KSM-66 root extract has the most RCTs for cortisol and stress reduction (24+ trials). Shoden extract has the strongest sleep and testosterone data. Sensoril has cognition trials but in small, narrow populations. Generic root powder has no comparable evidence base. Form, dose, and standardization percentage determine whether any effect exists.

Can ashwagandha damage your liver?

Yes — cholestatic liver injury is a documented adverse event. Björnsson et al. (2020, Liver International) published a 5-case series from Iceland and the U.S. Drug-Induced Liver Injury Network. Onset ranged from 2 to 12 weeks post-initiation. NIH LiverTox lists ashwagandha as a known hepatotoxic herb. The incidence is low relative to total users, but thousands of cases annually are plausible given 1 million monthly searches. Stop use immediately if you develop jaundice, dark urine, or upper-right abdominal pain.

Does ashwagandha actually raise testosterone?

In one specific population: yes. Lopresti et al. (2019) found a 14.7% greater testosterone increase vs. placebo in overweight men aged 40–70 with mild fatigue symptoms, using Shoden extract at 21 mg withanolide glycosides for 16 weeks. This finding does not generalize to young, lean, non-fatigued men. The claim that ashwagandha is a universal testosterone booster is not supported by the trial data.

How long should you take ashwagandha?

The best-designed trials run 8–16 weeks. Chandrasekhar 2012 used 60 days. Langade 2019 used 10 weeks. Lopresti 2019 used 16 weeks. Long-term safety beyond 16 weeks has not been established in well-controlled trials. The Danish Technical University raised hormonal disruption concerns at chronic doses. Liver injury cases include durations as short as 2 weeks — duration is not a safety proxy.

Why did Denmark ban ashwagandha?

Denmark's Veterinary and Food Administration formally banned ashwagandha from food supplements in April 2023, becoming the first European nation to do so. The cited basis was a 2020 risk assessment from the Technical University of Denmark flagging concerns about hormonal disruption and potential reproductive effects at physiological doses. The ban's reproductive-risk basis has been disputed by independent researchers. The liver injury documentation — 5-case series, Iceland + US DILIN, 2020 — is harder to dismiss and predates the ban.

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Sources

• Björnsson HK, Björnsson ES, Avula B, et al. (2020). Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver International. PubMed 31991029
• Bonilla DA, Moreno Y, Gho C, et al. (2021). Effects of Ashwagandha (Withania somnifera) on Physical Performance: Systematic Review and Bayesian Meta-Analysis. Sports (MDPI), 9(2), 20. PubMed 33670194
• 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. PubMed 23439798
• ConsumerLab.com. (2015). Ashwagandha Supplements Review — Product Testing Results. consumerlab.com
• Langade D, Kanchi S, Salve J, et al. (2019). Efficacy and Safety of Ashwagandha (Withania somnifera) Root Extract in Insomnia and Anxiety. Cureus, 11(9), e5797. PubMed 31728244
• Lopresti AL, Drummond PD, Smith SJ. (2019). A Randomized, Double-Blind, Placebo-Controlled, Crossover Study Examining the Hormonal and Vitality Effects of Ashwagandha in Aging, Overweight Males. American Journal of Men's Health. PubMed 30854916
• Lopresti AL, Smith SJ, Malvi H, Kodgule R. (2019). An Investigation into the Stress-Relieving and Pharmacological Actions of an Ashwagandha (Withania somnifera) Extract: A Randomized, Double-Blind, Placebo-Controlled Study. Medicine, 98(37), e17186. PubMed 31517876
• NCCIH — National Center for Complementary and Integrative Health. (2023). Ashwagandha: Usefulness and Safety. nccih.nih.gov
• NIH LiverTox. (2023). Ashwagandha. National Library of Medicine, NCBI. NBK548536
• ODS — NIH Office of Dietary Supplements. (2023). Ashwagandha: Is it helpful for stress, anxiety, or sleep? Health Professional Fact Sheet. ods.od.nih.gov
• Pingali U, Pilli R, Fatima N. (2014). Effect of Standardized Aqueous Extract of Withania somnifera on Tests of Cognitive and Psychomotor Performance. Pharmacognosy Research. PubMed 24914804
• Pratte MA, Nanavati KB, Young V, Morley CP. (2014). An Alternative Treatment for Anxiety: A Systematic Review of Human Trial Results Reported for the Ayurvedic Herb Ashwagandha. Journal of Alternative and Complementary Medicine, 20(12). PubMed 25405876