Benefits
Stress and Cortisol Balance
Helps the body adapt to stress and supports healthy cortisol levels. At 300 mg twice daily it has reduced perceived stress scores and lowered elevated cortisol versus placebo in chronically stressed adults.
Anxiety and Mood
In an 8-week trial of 60 stressed but healthy adults, 600 mg a day lowered Perceived Stress Scale scores, serum cortisol and Hamilton Anxiety scores more than placebo. A 250 mg a day arm did less, and its Hamilton Anxiety score did not separate from placebo. An independent meta-analysis pooling 12 ashwagandha trials in 1,002 people found significant reductions in anxiety and stress, but rated the certainty of that evidence as low, with wide variation between trials.
Sleep Quality
In a 10-week randomized trial of 60 people with insomnia and anxiety, 300 mg twice daily shortened sleep onset latency to 29.0 minutes against 33.9 minutes on placebo and improved sleep efficiency and Pittsburgh Sleep Quality Index scores. In healthy stressed adults, sleep quality also improved on a simple rating scale. It is not a sedative and does not work on the first night; changes build over weeks.
Memory and Focus
The one cognitive trial gave 300 mg twice daily for 8 weeks to 50 adults diagnosed with mild cognitive impairment, and found better immediate and general memory, executive function, sustained attention and processing speed than placebo. No KSM-66 trial has tested memory or focus in adults with normal cognition.
Strength, Endurance, and Recovery
In 57 untrained young men doing 8 weeks of resistance training, 300 mg twice daily produced larger gains in bench-press 1-RM (46.0 kg against 26.4 kg on placebo) and leg-extension 1-RM, larger arm and chest measurements, and a smaller rise in creatine kinase after exercise. In 50 healthy athletic adults, VO2 max rose 5.67 mL/kg/min from baseline over 12 weeks against 1.86 on placebo. Both trials were small, single-centre and manufacturer-linked.
Serum Testosterone and Sperm Measures
Serum testosterone was a secondary measure in the resistance-training trial, where it rose 96.2 ng/dL on KSM-66 against 18.0 ng/dL on placebo over 8 weeks in 57 untrained young men. The sperm count and motility findings come from a separate 90-day pilot in 46 men diagnosed with oligospermia, and they do not tell you what the extract does in fertile men. Ashwagandha is not a treatment for infertility or for low testosterone.
Mechanism of action
Stress and Anxiety Reduction
Serum cortisol fell in the human trials, which is consistent with damping of the hypothalamic-pituitary-adrenal axis. GABA receptor activity from withanolides is a laboratory finding and has not been measured in people.
Cognitive Enhancement
In animal and cell studies, withanolides inhibit acetylcholinesterase and so raise acetylcholine. It also reduces oxidative stress in the brain, protecting neurons and supporting synaptic plasticity.
Improved Sleep Quality
GABAergic activity is a laboratory finding for withanolides rather than something measured in the sleep trials, which recorded shorter sleep onset latency and better sleep efficiency by actigraphy. Its stress-reducing effects further support sleep by lowering cortisol-driven arousal.
Enhanced Physical Performance
Improved mitochondrial function and oxygen use are proposed from preclinical work; the human trials measured VO2 max, 1-RM strength, muscle size and serum creatine kinase, and no mitochondrial marker. It also reduces exercise-induced muscle damage by lowering oxidative stress and inflammation.
Testosterone and Fertility Support
Animal work reports increased activity of steroidogenic enzymes and antioxidant protection of testicular tissue. In people, the trials measured serum testosterone and semen parameters directly; the pathway connecting the two has not been demonstrated in humans.
Immune Effects (Laboratory and Animal Work Only)
Changes in natural killer cell activity and cytokine production have been reported in laboratory and animal work with Withania somnifera, not in the KSM-66 trials cited here. No trial on this page measured an immune outcome in people, so this remains a proposed mechanism only.
Clinical trials
Prospective, randomized, double-blind, placebo-controlled study of KSM-66 ashwagandha root extract (300 mg twice daily, 600 mg/day) vs placebo in 64 chronically stressed adults for 60 days. Outcomes: Perceived Stress Scale (PSS), DASS-21, serum cortisol, safety. (Indian J Psychol Med)
64 chronically stressed adults. 60-day intervention.
Perceived Stress Scale scores fell 44.0% from baseline in the KSM-66 group against 5.5% in placebo, and serum cortisol fell 27.9% from baseline against 7.9% in placebo, with both between-group differences statistically significant. DASS-21 subscales also improved. The 44% and 28% figures are changes from baseline inside the treated group, not the size of the gap over placebo. Generally well-tolerated. Critical context: this is the foundational stress trial heavily cited in ashwagandha marketing. Industry-funded (Ixoreal Biomed). Independent replication has been broadly supportive but with smaller effect sizes.
Randomized, double-blind, placebo-controlled pilot trial of ashwagandha root extract, 300 mg twice daily, vs placebo in 50 adults diagnosed with mild cognitive impairment, for 8 weeks. Outcomes: Wechsler Memory Scale III subtests, Eriksen Flanker task, Wisconsin Card Sort, Trail-Making part A, Mackworth Clock. (J Diet Suppl)
50 adults with diagnosed mild cognitive impairment, not healthy adults with ordinary memory complaints. 8-week intervention.
At 8 weeks the extract group improved more than placebo on immediate and general memory (Wechsler Memory Scale III logical memory, verbal paired associates, faces and family pictures) and on executive function, sustained attention and information-processing speed. The paper reports its outcomes after eight weeks of treatment. Because everyone in the trial had diagnosed mild cognitive impairment, it does not show what the extract does for memory in adults with normal cognition. The trial was manufacturer-linked, and the published report does not name the extract as KSM-66.
Systematic review and meta-analysis of five randomized placebo-controlled trials, 400 participants in total, of ashwagandha extracts from several different brands, including KSM-66 and Shoden. Cheah, Norhayati, Husniati Yaacob and Abdul Rahman, PLoS One 2021. This is a pooled analysis of other people's trials, not a study conducted in people.
Not a study population: five randomized trials totalling 400 adults, pooled across several different ashwagandha extracts.
The pooled effect on overall sleep was small but significant: standardized mean difference -0.59 (95% CI -0.75 to -0.42), with substantial variation between trials (I-squared 62%). Effects were larger in adults diagnosed with insomnia, at 600 mg/day or more, and at 8 weeks or longer. Mental alertness on rising and anxiety improved; quality of life did not. A KSM-66-specific sleep trial does exist separately: Langade and colleagues gave 300 mg twice daily for 10 weeks to 60 people with insomnia and anxiety and measured sleep onset latency of 29.0 minutes against 33.9 on placebo, with better sleep efficiency and PSQI scores.
Randomized, double-blind, placebo-controlled trial of KSM-66 (600 mg/day) vs placebo in 50 healthy athletic adults over 12 weeks. Outcomes: VO2 max measured on a 20 m shuttle run test, and the WHO self-reported quality-of-life questionnaire. No recovery marker was measured. (Ayu)
50 healthy athletic adults, of whom 24 on KSM-66 and 25 on placebo completed. 12-week intervention.
Mean VO2 max rose 4.91 mL/kg/min from baseline on KSM-66 against 1.42 on placebo at 8 weeks, and 5.67 against 1.86 at 12 weeks. Self-reported quality-of-life scores improved more on KSM-66. The widely quoted 13.6% figure is the within-group rise from baseline, not the advantage over placebo, and no recovery marker was measured. A change of this size from a botanical is large enough to need independent replication, and much ashwagandha performance marketing rests on this one small industry-funded trial.
Randomized, double-blind, placebo-controlled pilot trial of KSM-66 root extract, 675 mg/day in three divided doses, vs placebo in 46 men with oligospermia (21 treated, 25 placebo) for 90 days. Outcomes: sperm count, semen volume, sperm motility, serum testosterone and LH. (Evid Based Complement Alternat Med)
46 men diagnosed with oligospermia (sperm count under 20 million/mL), a clinical infertility population rather than healthy men. 90-day intervention.
From baseline to day 90 the treated group showed a 167% rise in sperm count, a 53% rise in semen volume, a 57% rise in motility and a 17% rise in serum testosterone (4.45 to 5.22 ng/mL); the paper describes the change in the placebo group as minimal. Every one of those percentages is a within-group change from baseline, not the gap over placebo. With 21 men treated, in a population with a diagnosed fertility problem, these numbers do not carry over to fertile men or to general testosterone support.
Randomized, double-blind, placebo-controlled pilot trial of KSM-66 root extract, 300 mg twice daily, vs placebo in 50 healthy women for 8 weeks. Outcomes: Female Sexual Function Index, Female Sexual Distress Scale, and the number of successful sexual encounters. Dongre, Langade and Bhattacharyya, BioMed Research International 2015.
50 healthy women. 8-week intervention.
FSFI total score and the arousal, lubrication, orgasm and satisfaction domains improved more than placebo, as did the sexual distress score and the number of successful sexual encounters. This was a 50-woman pilot at a single Indian centre with manufacturer involvement, and no hormones were measured, so the reason for the effect is unknown.
This entry is not a clinical trial. It combines manufacturer-sponsored genotoxicity and animal toxicity testing of KSM-66 with the published human case reports of liver injury from ashwagandha supplements.
Not applicable: laboratory and animal toxicology, plus case reports in people.
Manufacturer-sponsored testing reported no significant effect on blood counts or on liver, kidney and thyroid markers, and the trials on this page reported mild adverse events at rates similar to placebo. Against that, Bjornsson and colleagues described five cases of liver injury attributed to ashwagandha supplements in Liver International in 2020: all five developed jaundice 2 to 12 weeks after starting, the injury pattern was cholestatic or mixed, and liver tests returned to normal within 1 to 5 months. The NIH LiverTox database lists ashwagandha as a cause of drug-induced liver injury. The reaction appears rare and idiosyncratic. Stop taking it and seek medical advice if jaundice, dark urine, itching or persistent nausea develop.