Ingredient Guide
Ashwagandha: Benefits, Dosage, and What the Research Says
The most-studied adaptogen for stress. Strong human evidence for a calmer stress response and better sleep, more modest evidence elsewhere, and a few real safety details worth knowing.
Written by Jessica Medson
Ashwagandha (Withania somnifera) is an adaptogenic herb with an unusually solid base of human trials for a botanical. Its clearest benefit is supporting a healthy response to everyday stress, with a meta-analysis showing reduced perceived-stress scores and lower cortisol, and it also improves sleep quality in randomized studies. Claims about testosterone and strength are more preliminary, and a few real safety considerations (thyroid, liver, pregnancy) mean it is not a supplement to take casually.
Mg per Day
The Ashwagandha Dose Used in Human Trials
The most consistent stress and sleep results come from standardized root extract at 300 to 600 mg per day. Many budget products fall well below this range, which is one reason results vary so much between brands.
125mg
250mg
600mg
Standardized ashwagandha root extract per day
*Dose ranges reflect the standardized root extracts used in the human trials cited here. Higher-potency extracts (e.g. Shoden) show effects at lower milligram amounts.
What Is Ashwagandha?
Ashwagandha (Withania somnifera) is a small shrub used for centuries in Ayurvedic tradition and classed today as an adaptogen: a plant thought to help the body cope with stress. The active compounds are called withanolides, and the amount of them in a product depends heavily on the extract, which is why standardization matters so much.
Most quality research uses a standardized root extract, and the most-studied branded version is KSM-66. When you read that "ashwagandha lowers cortisol," it almost always means a standardized root extract at 300 to 600 mg per day, not just any capsule of ground root.
How Does Ashwagandha Work?
Ashwagandha's best-described effect is on the body's stress system, the HPA axis, which controls the release of the stress hormone cortisol. Across multiple trials, standardized extract lowered elevated morning cortisol, which is the leading explanation for why people report feeling calmer and more resilient.5 Unlike a stimulant or a sedative, an adaptogen is thought to help nudge an over-activated stress response back toward normal rather than forcing it in one direction.
Ashwagandha for Stress and Cortisol
This is ashwagandha's strongest evidence. In a landmark double-blind trial, adults with chronic stress taking 600 mg/day of standardized extract for 60 days had significantly lower stress scores and a substantial drop in serum cortisol versus placebo.1 A dose-ranging study found benefits at both 250 and 600 mg/day, with the larger dose producing the biggest cortisol reduction.2 Other trials using different standardized extracts reported roughly 20 to 40% reductions in stress and anxiety measures.56
Pulling it together, a 2024 meta-analysis of 9 randomized trials (558 people) found ashwagandha significantly reduced perceived-stress and anxiety scores and lowered serum cortisol compared with placebo.7 The honest framing: this supports a healthy stress response, it is not a treatment for a diagnosed anxiety condition, and the average effect, while real, is moderate.
Ashwagandha for Sleep
Ashwagandha also has good randomized evidence for sleep. In a 10-week trial, 600 mg/day shortened the time to fall asleep and improved sleep efficiency and overall sleep-quality scores versus placebo.3 A separate 12-week study in older adults found improvements in both sleep quality and general well-being.4 This fits the stress story: calmer evenings tend to mean easier sleep, which is why ashwagandha is a popular evening adaptogen.
Strength, Recovery, and Testosterone (Read This Carefully)
Ashwagandha is often marketed for muscle and testosterone, and here you should be more skeptical. A Bayesian meta-analysis of 12 trials found a meaningful benefit for strength, recovery, and fitness when ashwagandha was combined with training in healthy adults.9 So the strength-and-recovery angle has reasonable support, in the context of exercise.
The testosterone claim is weaker. It rests mainly on one small trial of 57 resistance-training men,8 and in another study the testosterone change was not statistically significant.5 So: ashwagandha may support healthy testosterone in active men, but call it what it is, early and not established, and be wary of any product promising a "testosterone boost."
Safety, Side Effects, and Who Should Avoid It
Ashwagandha is well tolerated in trials at 300 to 600 mg/day, but it has a few important exceptions that make it different from a basic vitamin.
Thyroid conditions. Ashwagandha can raise thyroid hormone levels. There is a documented case of a woman who developed thyroid overactivity (with a racing heart) after using it in place of her thyroid medication.12 If you have any thyroid condition or take thyroid medication, do not use ashwagandha without your doctor and thyroid monitoring.
Liver. Rare but real cases of liver injury have been reported, sometimes within one to two weeks of starting.1011 Everyone recovered after stopping, but stop use and seek care promptly if you notice jaundice (yellowing), dark urine, abdominal pain, or unusual fatigue.
Pregnancy and autoimmune conditions. Ashwagandha is traditionally avoided in pregnancy and breastfeeding, and standard guidance is not to use it during those periods.13 Because it can stimulate the immune system, people with autoimmune conditions or on immune-suppressing medication should also check with a provider first. It may add to the effect of sedatives, so mention it before any surgery.
Ashwagandha Dosage
The doses below reflect the standardized root extracts used in the human trials cited here. Take it with food, and give it several weeks: the stress and sleep effects build over 4 to 12 weeks rather than the first night.
| Goal | Typical Dose | Timing | Notes |
|---|---|---|---|
| Stress & cortisol support | 300-600 mg / day | With food (morning or evening) | Standardized root extract; KSM-66 is the most-studied. |
| Sleep support | 300-600 mg / day | Evening, with food | Give it 4 to 10 weeks to build. |
Higher-potency extracts (e.g. Shoden) work at lower milligram amounts. Not for use in pregnancy, breastfeeding, or with thyroid conditions without medical guidance.
Ashwagandha Evidence at a Glance
Where the human evidence is strong, and where it is early.
| Outcome | What the evidence shows | Strength |
|---|---|---|
| Stress & cortisol | Lower perceived stress and serum cortisol | Strong (multiple RCTs + meta-analysis) |
| Anxiety scores | Reduced anxiety-scale scores | Moderate |
| Sleep quality | Faster sleep onset, better sleep quality | Moderate |
| Strength & recovery (with training) | Improved strength and recovery | Moderate |
| Testosterone | Possible small increase in active men | Preliminary / not established |
Effect sizes are averages from the cited trials and vary by extract, dose, and person.
Frequently Asked Questions
What is ashwagandha good for?
Its best-supported use is supporting a healthy stress response: randomized trials and a meta-analysis show reduced perceived-stress and anxiety scores and lower cortisol. It also has good evidence for improving sleep quality. It is a supplement, not a treatment for any diagnosed condition.
How much ashwagandha should I take?
The most-studied dose is 300 to 600 mg per day of a standardized root extract (KSM-66 is the most-researched). Higher-potency extracts such as Shoden work at lower milligram amounts. Take it with food.
How long does ashwagandha take to work?
It builds over weeks, not hours. Most trials measured stress, cortisol, and sleep benefits over 8 to 12 weeks of daily use, so give it at least a month of consistent use.
Does ashwagandha really raise testosterone?
The evidence is early and mixed. One small trial in resistance-training men found an increase, but another study found no significant change. It may support healthy testosterone in active men, but it is not an established "testosterone booster."
Can ashwagandha affect the thyroid?
Yes, and this is an important caution. Ashwagandha can raise thyroid hormone levels, and there are documented cases of thyroid overactivity. If you have any thyroid condition or take thyroid medication, do not use it without your doctor and thyroid monitoring.
Is ashwagandha safe for the liver?
For most people, yes, but rare cases of liver injury have been reported, sometimes within a couple of weeks of starting. Everyone in those reports recovered after stopping. Stop use and seek care if you notice jaundice, dark urine, or unusual fatigue.
Can I take ashwagandha while pregnant?
No. Ashwagandha is traditionally avoided in pregnancy and breastfeeding, and standard guidance is not to use it during those periods. Consult your healthcare provider.
When should I take ashwagandha, morning or night?
Both work, since the stress and cortisol benefits build over weeks regardless of timing. Many people take it in the evening because of the calming and sleep effects. Consistency matters more than the exact hour.
Should I take ashwagandha every day or cycle it?
Trials generally used continuous daily dosing for 8 to 12 weeks with good tolerability. Some people cycle it (for example a few months on, a few weeks off); both approaches are reasonable. If you use it long-term, periodic check-ins with your provider are sensible.
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Scientific References
- 1.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 Journal of Psychological Medicine. 2012. PubMed: 23439798Clinical (RCT / meta-analysis)
- 2.Salve J, Pate S, Debnath K, Langade D. Adaptogenic and anxiolytic effects of ashwagandha root extract in healthy adults: a double-blind, randomized, placebo-controlled clinical study. Cureus. 2019. PubMed: 32021735Clinical (RCT / meta-analysis)
- 3.Langade D, et al. Efficacy and safety of ashwagandha root extract in insomnia and anxiety: a double-blind, randomized, placebo-controlled study. Cureus. 2019. PubMed: 31728244Clinical (RCT / meta-analysis)
- 4.Kelgane SB, Salve J, Sampara P, Debnath K. Efficacy and tolerability of ashwagandha root extract in the elderly for improvement of general well-being and sleep. Cureus. 2020. PubMed: 32226684Clinical (RCT / meta-analysis)
- 5.Lopresti AL, Smith SJ, Malvi H, Kodgule R. An investigation into the stress-relieving and pharmacological actions of an ashwagandha extract: a randomized, double-blind, placebo-controlled study. Medicine (Baltimore). 2019. PubMed: 31517876Clinical (RCT / meta-analysis)
- 6.Majeed M, Nagabhushanam K, Mundkur L. A standardized ashwagandha root extract alleviates stress, anxiety, and improves quality of life in healthy adults by modulating stress hormones. Medicine (Baltimore). 2023. PubMed: 37832082Clinical (RCT / meta-analysis)
- 7.Arumugam V, et al. Effects of ashwagandha (Withania somnifera) on stress and anxiety: a systematic review and meta-analysis. Explore (NY). 2024. PubMed: 39348746Clinical (RCT / meta-analysis)
- 8.Wankhede S, et al. Examining the effect of Withania somnifera supplementation on muscle strength and recovery: a randomized controlled trial. Journal of the International Society of Sports Nutrition. 2015. PubMed: 26609282Clinical (RCT / meta-analysis)
- 9.Bonilla DA, et al. Effects of ashwagandha (Withania somnifera) on physical performance: systematic review and Bayesian meta-analysis. Journal of Functional Morphology and Kinesiology. 2021. PubMed: 33670194Clinical (RCT / meta-analysis)
- 10.Tóth M, Benedek AE, Longerich T, Seitz HK. Ashwagandha-induced acute liver injury: a case report. Clinical Case Reports. 2023. PubMed: 36937644Preclinical (animal / cell)
- 11.Ireland PJ, Hardy T, Burt AD, Donnelly MC. Drug-induced hepatocellular injury due to herbal supplement ashwagandha. Journal of the Royal College of Physicians of Edinburgh. 2021. PubMed: 34882134Preclinical (animal / cell)
- 12.Kamal HI, et al. Ashwagandha as a unique cause of thyrotoxicosis presenting with supraventricular tachycardia. Cureus. 2022. PubMed: 35475098Preclinical (animal / cell)
- 13.Tallon MJ, Koturbash I, Blum JL. A systematic and ethnobotanical review of ashwagandha's (Withania somnifera) teratogenic and abortifacient potentials. Phytotherapy Research. 2025. PubMed: 40887707Human observational