Nutrition
Ashwagandha lowered cortisol and stress scores in placebo-controlled trials; sleep, testosterone and thyroid data are smaller. The trials worth knowing, the doses they used and who should avoid it.
Key takeaways
Ashwagandha (Withania somnifera) is an ancient Ayurvedic herb that has outlasted every wellness trend of the past decade — and with good reason. Unlike many adaptogens that rely on centuries-old tradition and a handful of small studies, ashwagandha has been tested in placebo-controlled RCTs with unusually large effect sizes for a supplement — worth reading critically, since most trials are small, short and run by a handful of groups.
This deep-dive covers the actual mechanisms, the specific studies worth knowing, what it will and won’t do, and the dosing strategy that the evidence supports.
Ashwagandha is a small shrub native to India, North Africa, and the Mediterranean. Its root has been used in Ayurvedic medicine for over 3,000 years under the name “Indian ginseng” — though it’s botanically unrelated to true ginseng.
The active compounds are primarily withanolides — steroidal lactones concentrated in the root. The most studied is withaferin A, along with withanolide D, withanolide A, and withanoside IV. Root extract standardizations in clinical trials typically target 5–10% withanolides.
The key mechanism: ashwagandha appears to act as a cortisol-lowering adaptogen through HPA axis modulation, while also interacting with GABA receptors, influencing thyroid hormone signaling, and reducing inflammatory markers including NF-κB and IL-6.
This is where ashwagandha earns its most credible standing.
The most-cited study remains Chandrasekhar et al., 2012 (Indian Journal of Psychological Medicine). 64 chronically stressed adults received either 300mg KSM-66 ashwagandha extract (twice daily) or placebo for 60 days.
Results: - 44% reduction in Perceived Stress Scale scores (vs 5.5% in placebo) - Serum cortisol reduced by 27.9% vs 7.9% in placebo group - All General Health Questionnaire subscales improved significantly
This is a large effect size for a nutritional supplement. The placebo reduction was modest, and the between-group difference was statistically significant (p < 0.001 across all primary endpoints).
Pratte et al. (2014, J Altern Complement Med) reviewed five human trials and found every one reported greater reductions in anxiety or stress scores with ashwagandha than placebo. Separately, a 60-day trial of a root-and-leaf extract (Auddy et al., 2008) reported serum cortisol reductions of up to 30.5% at 250 mg twice daily, with significant improvements in anxiety, energy, and social functioning.
The cortisol-lowering effect doesn’t appear to simply suppress the HPA axis uniformly. Rather, ashwagandha seems to reduce dysregulated cortisol output — the excess secretion during chronic psychological stress — without blunting acute cortisol responses needed for normal functioning. This is the classic adaptogen definition: buffering the extremes without disrupting normal physiology.
Several trials have specifically tested anxiety outcomes.
Lopresti et al. 2019 (Medicine): 60 stressed adults received 240 mg/day of a standardized extract (Shoden) or placebo for 60 days. Hamilton Anxiety Rating Scale scores fell 41% vs 24%. The treatment group showed no significant adverse effects.
Andrade et al. 2000 (Indian Journal of Psychiatry): 39 patients with anxiety disorders received an ethanolic root extract (250 mg twice daily) or placebo for six weeks. Significant reductions in anxiety (Hamilton scores) were seen within 2 weeks, with continued improvement at 6 weeks.
Mechanism: The anxiolytic effects likely involve GABAergic pathways. Withanolides have affinity for GABA-A receptor sites, which may explain the calming-without-sedation profile that distinguishes ashwagandha from drugs like benzodiazepines.
Important caveat: Ashwagandha is not a replacement for clinical anxiety treatment. These studies enrolled people with elevated stress or mild-to-moderate anxiety, not generalized anxiety disorder (GAD) or panic disorder. Clinical anxiety disorders require clinical evaluation.
The sleep evidence is surprisingly strong, and often overlooked in the adaptogens literature.
Deshpande et al. 2020 (Sleep Medicine): 150 healthy adults with non-restorative sleep received 120 mg/day of a standardized extract (Shoden) or placebo for 6 weeks. In the healthy cohort, sleep onset latency decreased by 6.6 minutes and sleep efficiency improved by 6.7%. In the insomnia subgroup, results were significantly larger.
Langade et al. 2019 (Cureus): 60 patients with insomnia received 300mg KSM-66 twice daily for 10 weeks. Sleep quality index (PSQI) improved by 72% in the treatment group vs 29% in placebo. Total sleep time increased significantly.
The likely mechanism: the GABAergic activity mentioned above, combined with cortisol reduction (raised evening cortisol is associated with poor sleep), is the proposed route to better sleep quality — particularly in people whose sleep issues are stress-driven.
This is why ashwagandha is often suggested for the “wired and tired” profile — high stress, hypervigilant nervous system, difficulty falling asleep.
This is the most-searched application and the evidence is real, though more nuanced than supplement companies suggest.
57 men aged 18–50 received 300mg KSM-66 twice daily or placebo for 8 weeks while participating in a resistance training program. Results: - Testosterone increased by 96.2 ng/dL in treatment group vs 18.2 ng/dL in placebo - Muscle strength, size and recovery (lower creatine kinase) also improved versus placebo
The testosterone change (~17% from baseline in one 8-week trial of resistance-training men) has not been shown to change symptoms or outcomes, but the study enrolled healthy men in a resistance training context. Effect may be smaller in sedentary populations.
Chronic cortisol elevation directly suppresses testosterone synthesis. Chronic cortisol elevation is associated with lower testosterone; the mechanisms (central suppression of GnRH/LH and direct effects on the testes) are still being worked out. When ashwagandha lowers cortisol, testosterone production has more room to operate. This is different from a direct testosterone-boosting effect — it’s more accurately described as removing a hormonal suppressor.
This explains why effects tend to be larger in stressed, sleep-deprived men than in well-rested, low-stress individuals.
Ahmad et al. 2010 (Fertility and Sterility): 75 infertile men received ashwagandha root powder (5 g/day) for 3 months; Mahdi et al. 2011 (Evid Based Complement Alternat Med) reported similar semen-quality changes in men with stress-related infertility. Sperm count, motility, and morphology all improved significantly, with concurrent reductions in seminal oxidative stress markers.
The cognitive evidence is earlier-stage but promising.
Choudhary et al. 2017 (Journal of Dietary Supplements): 50 adults received 300mg KSM-66 twice daily for 8 weeks. Results showed significant improvements in immediate memory, general memory, executive function, and information processing speed compared to placebo.
Mechanism: Multiple pathways likely contribute — withanolide A promotes axon growth and synaptic density in the hippocampus in animal models. Combined with cortisol reduction (high chronic cortisol atrophies hippocampal volume), the effect on memory and learning makes mechanistic sense.
This is an area where more large-scale human RCTs are needed, but the existing evidence is directionally positive.
Beyond the testosterone/muscle data above, several studies have examined performance outcomes directly.
Shenoy et al. 2012: Healthy cyclists given 500mg ashwagandha root twice daily showed significantly improved VO2 max, cardiorespiratory endurance, and time-to-exhaustion compared to placebo.
Ziegenfuss et al. 2018 (Nutrients, STAR trial): 38 recreationally active men taking 500 mg/day of a root-and-leaf extract for 12 weeks showed greater 1-RM squat and bench-press gains vs placebo (muscle strength outcomes), alongside improved recovery (lower CK elevation post-exercise).
One area competitors often ignore: ashwagandha measurably affects thyroid hormone levels.
Sharma et al. 2018 (Journal of Alternative and Complementary Medicine): 50 adults with subclinical hypothyroidism received 600mg of ashwagandha root extract for 8 weeks. T3 rose about 41%, T4 about 20%, and TSH fell about 17% in the treatment group.
What this means: This is a single small trial in subclinical hypothyroidism and is not a basis for self-treating any thyroid condition. For people on thyroid medication (levothyroxine, T3), this could cause problematic additive effects. For people with Hashimoto’s (autoimmune hypothyroidism), the evidence is unclear — there’s some concern that immune-modulating effects could exacerbate autoimmunity in some individuals.
Practical rule: If you’re on any thyroid medication or have diagnosed thyroid disease, discuss ashwagandha with your doctor before starting.
Most positive clinical trials have used one of two protocols:
Standard dose (most common in RCTs): - 300mg of KSM-66 or Sensoril ashwagandha extract twice daily (600mg total) - Standardized to 5% withanolides (KSM-66) or 10% withanolides (Sensoril) - Taken with meals to improve tolerability
Full-root powder dose: - 5–6g/day of whole root powder - Traditional Ayurvedic dosing; used in fertility and athletic studies - Less practical but traditional preparations show efficacy
Timing notes: - For sleep improvement: one dose at night, taken 30–60 minutes before bed - For stress/cortisol: split dosing (morning and evening) used in most studies - Effects typically require 4–8 weeks of consistent use to fully manifest
The supplement market is saturated with ashwagandha, and not all products are equivalent.
| Extract | Standardization | Part Used | Most Studied For |
|---|---|---|---|
| KSM-66 | ≥5% withanolides | Root only | Testosterone, stress, cognition |
| Sensoril | ≥10% withanolides | Root + leaf | Stress, sleep, anxiety |
| Generic root extract | Variable | Root | Varies |
| Whole root powder | Not standardized | Root | Traditional use, fertility |
KSM-66 is the most-studied extract and has the largest body of double-blind RCT evidence. Sensoril (higher withanolide concentration, using both root and leaf) has strong stress and anxiety data. Both are legitimate choices; generic extracts without standardization are unreliable.
Ashwagandha has a strong safety profile at standard doses. Key considerations:
Populations studied (up to 12 weeks in most trials): - Healthy stressed adults at 300-600 mg/day - Men in resistance-training programs - Adults with poor or non-restorative sleep - Athletes in resistance training programs
Use with caution or avoid if: - Pregnant — ashwagandha has traditionally been used to induce abortion (abortifacient effects confirmed in animal models); avoid during pregnancy - Thyroid medication — potential additive thyroid effects - Autoimmune conditions (lupus, multiple sclerosis, Hashimoto’s) — immune-modulating properties may be bidirectional - Sedative medications — additive CNS depressant effects possible - Barbiturates / benzodiazepines — GABAergic interaction may enhance sedation
Rare but reported side effects: Drowsiness (particularly at higher doses), GI upset if taken without food, and a growing number of liver injury case reports (Björnsson et al., 2020; NIH LiverTox), several at ordinary supplement doses. Stop and seek care if you develop jaundice, dark urine, itching or abdominal pain, and avoid ashwagandha entirely if you have liver disease.
A common mistake — partly driven by supplement marketing:
Most coverage of ashwagandha (Examine.com, Healthline, WebMD) lists the studies and dosing but doesn’t connect the mechanistic threads. Here’s what matters:
The cortisol-testosterone axis is the key. Ashwagandha doesn’t operate through one mechanism — it works because chronic stress dysregulates multiple downstream systems simultaneously (sleep, testosterone, cognition, immune function), and cortisol reduction is the common upstream intervention. This is why studies show improvements across seemingly unrelated domains.
Who benefits most: People with stress-driven health issues — poor sleep in high-pressure periods, low testosterone with documented cortisol elevation, anxiety in the context of life circumstances rather than clinical pathology. For people without significant cortisol dysregulation, effects will be smaller.
Stack context: See our Tongkat Ali deep-dive for how these two adaptogens compare — no trial has tested the two together, so any additive effect is a hypothesis. For stress specifically, see how adaptogens as a class work.
Ashwagandha has one of the strongest evidence bases of any adaptogen:
Trials mostly used a standardized root extract at 300 mg twice daily with food for 8-12 weeks, with effects building over 4-8 weeks. Talk to a clinician first if you are pregnant, take thyroid, sedative, immunosuppressant or diabetes medication, or have liver disease. The evidence supports it as one of the better-studied supplements available.
This article is for general education and is not medical advice.
Sources: Chandrasekhar et al. 2012, Indian J Psychol Med | Pratte et al. 2014, J Altern Complement Med | Auddy et al. 2008, JANA | Lopresti et al. 2019, Medicine | Andrade et al. 2000, Indian J Psychiatry | Deshpande et al. 2020, Sleep Med | Langade et al. 2019, Cureus | Wankhede et al. 2015, JISSN | Ahmad et al. 2010, Fertil Steril | Choudhary et al. 2017, J Diet Suppl | Shenoy et al. 2012, J Ayurveda Integr Med | Ziegenfuss et al. 2018, Nutrients | Sharma et al. 2018, J Altern Complement Med | Björnsson et al. 2020, Liver Int | Meta-analysis PMC12242034
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