What Does Ashwagandha Do for the Body? Effects, Evidence & Dosage
Automated draft updated
Ashwagandha (Withania somnifera) is an adaptogenic herb that helps the body regulate its stress response, primarily by modulating the hypothalamic-pituitary-adrenal (HPA) axis and reducing cortisol levels. Clinical trials support its use for stress, sleep quality, physical endurance, and cognitive function, with effects typically emerging after 4–8 weeks of consistent use.
How Ashwagandha Works in the Body
The active compounds in ashwagandha are withanolides — steroidal lactones concentrated in the root and, to a lesser extent, the leaves. These compounds interact with glucocorticoid receptors, GABAergic signalling pathways, and the thyroid axis. By dampening overactivation of the HPA axis, withanolides help reduce the excessive cortisol output associated with chronic stress. This mechanism underpins most of ashwagandha's documented benefits, from mood stabilisation to improved sleep onset.
Standardised extracts such as KSM-66 (root-only, ≥5% withanolides) and Sensoril (leaf and root blend, ≥10% withanolides) are the most rigorously studied forms. Shoden, standardised to 35% withanolides, is the highest-concentration extract currently available and has demonstrated effects at lower doses (120 mg/day in some trials).
What the Clinical Evidence Shows
Stress and anxiety: A 2019 randomised controlled trial using KSM-66 ashwagandha found that 240 mg/day significantly reduced serum cortisol and self-reported stress scores compared to placebo over 60 days. Multiple trials with Sensoril ashwagandha have replicated reductions in perceived stress and anxiety (PSS and HAM-A scales).
Sleep quality: Ashwagandha appears to improve sleep latency and non-REM sleep quality, likely via triethylene glycol content and GABAergic activity. Studies using KSM-66 at 300 mg twice daily showed significant improvements in sleep efficiency in adults with insomnia.
Physical performance: In resistance-trained individuals, ashwagandha supplementation over 8–12 weeks has been associated with greater gains in muscle strength, VO₂ max, and recovery. These effects are attributed partly to cortisol reduction and partly to a modest anabolic effect via testosterone and luteinising hormone modulation.
Cognitive function: Early evidence suggests withanolides support neuroprotection and working memory, though this area requires larger trials. Shoden ashwagandha has shown promising results in healthy adults on reaction time and memory tasks.
Thyroid and hormonal health: Some research indicates ashwagandha can modestly increase T3 and T4 levels in subclinical hypothyroidism, and may support testosterone levels in men with stress-related hormonal imbalance. This should be discussed with a clinician before use by anyone on thyroid medication.
Dosage Guidance
Effective doses vary by extract and concentration:
- Full-spectrum or less standardised root powder: 3,000–6,000 mg/day (divided doses)
- KSM-66 (≥5% withanolides): 300–600 mg/day
- Sensoril (≥10% withanolides): 125–250 mg/day
- Shoden (35% withanolides): 120–240 mg/day
Dosing in the evening may enhance sleep benefits. Most studies run 8–12 weeks; long-term safety data beyond 6 months is limited but generally reassuring.
Safety and Considerations
Ashwagandha is well-tolerated in most healthy adults. Reported side effects are mild and include gastrointestinal discomfort at high doses and, rarely, drowsiness. A small number of case reports have linked high-dose supplementation to liver enzyme elevations; individuals with pre-existing liver conditions should exercise caution.
Contraindications include: pregnancy (uterotonic effects reported), autoimmune conditions (immunostimulant properties may be relevant), and concurrent use of sedatives, thyroid medications, or immunosuppressants. Always consult a healthcare provider before starting supplementation if you are on medication.
Practical Use
For most people, a standardised extract taken with food once or twice daily is the most reliable approach. Traditional preparations like ashwagandha tea or herbal ashwagandha latte offer lower, more variable doses suited to general wellness rather than therapeutic targets. Ashwagandharishta, an Ayurvedic fermented formulation, remains widely used in traditional practice. Allow at least 4 weeks before evaluating response.
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Frequently asked questions
How long does ashwagandha take to work?
Most clinical trials report measurable effects on stress, sleep, and cortisol after 4–8 weeks of daily supplementation. Some individuals notice improvements in sleep quality within the first two weeks, while physical performance benefits typically emerge after 8–12 weeks.
Is ashwagandha safe to take every day?
Daily use appears safe for most healthy adults over study periods of up to 3 months. Rare cases of liver enzyme elevation have been reported, so individuals with liver conditions or those taking hepatotoxic medications should seek medical advice before use.
What is the difference between KSM-66 and Sensoril ashwagandha?
KSM-66 is a root-only extract standardised to ≥5% withanolides, most studied for stress, physical performance, and testosterone support. Sensoril uses both root and leaf material, standardised to ≥10% withanolides, and is more commonly studied for stress reduction and cognitive calm at lower doses.
Can ashwagandha help with anxiety?
Several randomised controlled trials show ashwagandha significantly reduces self-reported anxiety scores and serum cortisol compared to placebo. Its anxiolytic effects are thought to involve GABAergic modulation and HPA axis regulation, though it is not a replacement for clinical treatment of anxiety disorders.