Ashwagandha: the evidence for stress, sleep and testosterone
Ashwagandha (Withania somnifera) is the rare herbal supplement with a real, if imperfect, evidence base. The strongest signal is for stress and anxiety: several short randomised trials show lower perceived stress and a modest fall in cortisol. The sleep effect is smaller but consistent, and clearest in people with insomnia. The testosterone findings are genuinely mixed and modest. None of this is risk-free: there are rare but serious reports of liver injury, possible thyroid effects, and clear reasons to avoid it in pregnancy and alongside certain conditions and medicines.
Key facts
- An international psychiatric taskforce (WFSBP and CANMAT, 2022) gives ashwagandha root extract a provisional, weak recommendation for generalised anxiety disorder at 300 to 600 mg/day, pending better data.1
- The most-cited stress trial reported a 27.9% drop in serum cortisol on 600 mg/day of KSM-66 over 60 days versus placebo.2
- A 2021 meta-analysis of five sleep trials (372 adults) found a small but significant improvement in sleep, strongest at ≥600 mg/day for ≥8 weeks.3
- Liver-injury reports led the US LiverTox database to rate ashwagandha a "likely" cause of rare clinically apparent liver injury (likelihood score B).4
- Denmark banned ashwagandha in supplements in 2023; France's ANSES advised against it in pregnancy, breastfeeding and endocrine disorders in 2024.5
What ashwagandha is, and the "adaptogen" idea
Ashwagandha is an evergreen shrub used for centuries in Ayurvedic medicine, where its root is classed as an adaptogen: a loosely defined term for a substance said to help the body resist a range of stressors. That label is traditional rather than a precise pharmacological category, so treat it as a starting hypothesis, not a mechanism. The active chemistry is better defined: the root is rich in steroidal lactones called withanolides, which are thought to underlie most effects, though preclinical work suggests other components contribute too.6 Most quality trials use standardised root extracts, the two best-studied being KSM-66 (root only) and Sensoril or Shoden (root and leaf), standardised to a fixed withanolide content. Because products differ so much, evidence for one extract does not automatically transfer to another. For how supplements fit a wider plan, see our health library.
The strongest evidence: stress, anxiety and cortisol
This is where ashwagandha earns its reputation. The landmark trial, Chandrasekhar and colleagues in 2012, randomised 64 chronically stressed adults to 300 mg of KSM-66 twice daily (600 mg/day) or placebo for 60 days. The extract group showed large falls on stress questionnaires and a 27.9% reduction in serum cortisol, the main stress hormone, versus placebo.2 A 2022 systematic review and dose-response meta-analysis by Akhgarjand and colleagues pooled the randomised trials and found significant reductions in both anxiety and stress scores, while stating plainly that higher-quality studies are still needed to confirm the effect.7
The honest caveats matter. As the US National Institutes of Health summarises, the supportive trials are mostly small, short (6 to 8 weeks), and conducted in India, often within a traditional-medicine setting, and many are funded by extract manufacturers.6 Not every trial is positive: a 2023 Australian study of a different extract found no reduction in perceived stress, though it did ease fatigue.6 So the direction of effect is encouraging and biologically plausible, but the evidence base is not yet robust. If your interest is the stress axis itself, our piece on cortisol and the HPA axis covers the wider picture.
Evidence strength, plainly. Stress and anxiety, short term: moderate (several RCTs and a meta-analysis, but small and largely industry-linked). Sleep, especially in insomnia: low-to-moderate. Testosterone in men: weak and inconsistent. Long-term safety beyond about 3 months: not established.
The sleep signal
The species name somnifera means "sleep-inducing", and modern data offer partial support. A 2021 systematic review and meta-analysis by Cheah and colleagues pooled five randomised trials (372 adults) and found a small but statistically significant improvement in overall sleep, with a standardised mean difference of about -0.59.3 The benefit was more pronounced in people diagnosed with insomnia, at doses of 600 mg/day or more, and over at least eight weeks. Some trials used objective actigraphy (a wrist motion monitor) and saw improvements in sleep efficiency and the time taken to fall asleep, not just self-reported quality.6 As with the stress data, the trials are small and Indian, so read the effect as real but modest. Magnesium is a common alternative people compare it against; we cover that in our magnesium for sleep and stress article.
The modest, mixed testosterone findings
Testosterone is where marketing most outruns the evidence. A 2021 systematic review of herbs and testosterone in men, led by Smith and Lopresti, found ashwagandha among the more promising botanicals but with inconsistent results across extracts.8 One trial of 675 mg/day of KSM-66 reported a roughly 17% rise in testosterone over 90 days, whereas a trial of 240 mg/day of Shoden found no significant change.8 A 2019 crossover study by Lopresti and colleagues in overweight, fatigued men aged 40 to 70 found a modest increase in testosterone and DHEA-S after eight weeks.9 The pattern suggests any hormonal effect is small, extract-dependent, and may be largest in men who are stressed, tired or carrying excess weight, rather than in healthy young men chasing a performance edge.
| Use | Typical dose studied | What the evidence shows | Strength |
|---|---|---|---|
| Stress / anxiety | 300 to 600 mg/day root extract | Lower stress scores; cortisol fell ~28% in the key trial27 | Moderate |
| Sleep | ≥600 mg/day, ≥8 weeks | Small but significant gain (SMD ~ -0.59); best in insomnia3 | Low to moderate |
| Testosterone (men) | 240 to 675 mg/day | Mixed: ~17% rise with one KSM-66 trial, none with Shoden89 | Weak / inconsistent |
| Generalised anxiety disorder | 300 to 600 mg/day (root, 5% withanolides) | Provisional, weak recommendation by WFSBP/CANMAT taskforce1 | Provisional |
Doses and forms
Across the better trials, the practical range is 300 to 600 mg/day of a standardised root extract (commonly standardised to 5% withanolides), often split into two doses and trialled for at least 8 weeks.16 KSM-66 is the most-studied root-only extract; Sensoril and Shoden are root-and-leaf extracts standardised to higher withanolide levels and used at lower milligram doses. Because preparations are not interchangeable, it is worth matching the product and dose to what was actually tested. Whole dried-root powder has been used at much higher doses traditionally, but the modern evidence sits with standardised extracts. If you are weighing this against other supplements, our stack builder helps avoid stacking several products aimed at the same goal.
Safety, honestly. Ashwagandha is generally well tolerated for up to about 3 months, with mild effects such as loose stools, nausea and drowsiness; long-term safety is unknown.6 Rare but serious liver injury has been reported, usually 2 to 12 weeks in, with jaundice; most cases resolve on stopping, but a few have caused liver failure, especially with pre-existing liver disease, so avoid it if you have cirrhosis or chronic liver disease.4 It may alter thyroid function (raising thyroid hormones, lowering TSH), so be cautious if you have a thyroid condition or take thyroid medication.10 Avoid in pregnancy and breastfeeding.5 It can interact with sedatives, antidiabetic and blood-pressure drugs, and immunosuppressants, and because it may raise testosterone, experts advise against use in hormone-sensitive prostate cancer.6 Stop and seek medical help for jaundice, dark urine, severe nausea or right-upper-abdominal pain.
Who might reasonably try it, and who should not
On current evidence, ashwagandha is most defensible as a short trial for everyday stress, anxiety symptoms or poor sleep in an otherwise healthy adult, using a standardised root extract at 300 to 600 mg/day for 8 to 12 weeks, then reviewing honestly whether it helped. It is not a treatment for a diagnosed mental-health condition on its own, and it should not replace care your GP recommends. The people who should steer clear, or only proceed with medical advice, are those with liver or thyroid disease, anyone pregnant or breastfeeding, men with prostate cancer, and people on interacting medicines. New to changing your routine? Our getting-started guide covers trialling one thing at a time so you can actually tell what works.
What to ask your GP
- Given my medical history, is ashwagandha safe for me, particularly any liver or thyroid concern?
- Could it interact with my current medicines (for example thyroid, diabetes, blood pressure or sedatives)?
- I am pregnant, breastfeeding or trying to conceive: should I avoid it?
- If I try it, what symptoms should make me stop straight away?
References
- Sarris J, Ravindran A, Yatham LN, et al. Clinician guidelines for the treatment of psychiatric disorders with nutraceuticals and phytoceuticals: the WFSBP and CANMAT Taskforce. World J Biol Psychiatry. 2022. PMID 35311615.
- Chandrasekhar K, Kapoor J, Anishetty S. 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 J Psychol Med. 2012. PMC3573577.
- Cheah KL, Norhayati MN, Husniati Yaacob L, Abdul Rahman R. Effect of ashwagandha (Withania somnifera) extract on sleep: a systematic review and meta-analysis. PLoS One. 2021. PMC8462692.
- LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Ashwagandha. National Institute of Diabetes and Digestive and Kidney Diseases, updated 2024. NBK548536.
- McKeown M. Why did Denmark ban ashwagandha? McGill University Office for Science and Society, 2023. mcgill.ca.
- National Institutes of Health, Office of Dietary Supplements. Ashwagandha: is it helpful for stress, anxiety, or sleep? Health Professional Fact Sheet, 2025. ods.od.nih.gov.
- Akhgarjand C, Asoudeh F, Bagheri A, et al. Does ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials. Phytother Res. 2022. PMID 36017529.
- Smith SJ, Lopresti AL, Teo SYM, Fairchild TJ. Examining the effects of herbs on testosterone concentrations in men: a systematic review. Adv Nutr. 2021. PMID 33150931.
- Lopresti AL, Drummond PD, Smith SJ. A randomized, double-blind, placebo-controlled, crossover study examining the hormonal and vitality effects of ashwagandha (Withania somnifera) in aging, overweight males. Am J Mens Health. 2019. PMID 30854916.
- Sharma AK, Basu I, Singh S. Efficacy and safety of ashwagandha root extract in subclinical hypothyroid patients: a double-blind, randomized placebo-controlled trial. J Altern Complement Med. 2018. PMID 28829155.
This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.