Ashwagandha (Withania somnifera)
An adaptogenic herb for stress resilience and hormonal balance
Quick Answer
Ashwagandha is an Ayurvedic adaptogen with good evidence for reducing cortisol (14-28% in studies), lowering stress/anxiety, and modestly increasing testosterone in men (10-15%). KSM-66 and Sensoril are the most-studied standardized extracts. Typical dose: 300-600mg KSM-66 or 125-250mg Sensoril daily. Effects are noticeable within 4-8 weeks. Cycle off periodically (8 weeks on, 2-4 weeks off).
Medium Evidence
Good studies, but more research needed
Safety: Generally safe for most adults. Some concerns about thyroid effects and rare liver issues.
What Is This?
Ashwagandha (Withania somnifera) is an herb that has been used in Ayurvedic medicine for over 3,000 years. Its name comes from Sanskrit meaning "smell of the horse," reflecting both its distinctive smell and traditional belief that it gives the strength and vitality of a horse.
It's classified as an adaptogen, a substance that helps the body adapt to stress and normalize physiological functions. The active compounds are called withanolides.
Standardized extracts (most researched):
- KSM-66: Full-spectrum root extract, 5% withanolides. Most studied for stress, testosterone, and athletic performance.
- Sensoril: Root and leaf extract, 10% withanolides. More sedating; best for anxiety and sleep.
How It Works
Ashwagandha modulates the stress response and hormones through several mechanisms:
Cortisol Reduction: Multiple studies show ashwagandha reduces cortisol by 14-28%. This is likely mediated through effects on the HPA axis (hypothalamic-pituitary-adrenal axis) that regulates stress hormones.
GABA Modulation: Withanolides appear to enhance GABAergic signaling, which may explain ashwagandha's calming effects.
Testosterone Support: In men with low-normal testosterone, ashwagandha consistently shows modest increases (10-15%) in multiple studies. Mechanisms may include improved Leydig cell function and reduced cortisol's testosterone-suppressing effects.
Thyroid Function: Ashwagandha may increase T3 and T4 thyroid hormones, which could boost metabolism but requires caution in those with thyroid conditions.
Anti-inflammatory: Contains compounds that reduce inflammatory markers like CRP and IL-6.
Research summary:
- Strong evidence for stress/anxiety reduction
- Moderate evidence for cortisol reduction
- Moderate evidence for testosterone increase in men
- Some evidence for improved sleep quality
- Mixed evidence for athletic performance
How to Start
Choose a standardized extract
Use KSM-66 or Sensoril rather than generic ashwagandha powder. These are the forms used in clinical trials and have consistent potency. KSM-66 is more versatile; Sensoril is more sedating.
Tips:
- •For stress + energy: KSM-66 (300-600mg daily)
- •For anxiety + sleep: Sensoril (125-250mg daily)
- •Avoid generic "ashwagandha root powder" with no standardization
Start with a moderate dose
Begin with 300mg KSM-66 once daily or 125mg Sensoril. Take with food. Assess tolerance for 1-2 weeks before increasing if needed.
Tips:
- •KSM-66: 300mg once or twice daily (with breakfast and/or dinner)
- •Sensoril: 125-250mg once daily (evening if using for sleep)
- •Higher doses aren't necessarily better, find your minimum effective dose
Give it 4-8 weeks
Ashwagandha's effects build over time. Stress reduction and mood benefits may appear within 2-4 weeks; hormonal effects take longer. Don't expect immediate results.
Tips:
- •Keep a simple stress/mood diary to track changes
- •Cortisol and testosterone changes are measurable at 8 weeks
- •If no benefit after 8-12 weeks, it may not be effective for you
Cycle on and off
Most practitioners recommend cycling ashwagandha (8 weeks on, 2-4 weeks off) rather than continuous use. This prevents tolerance and allows assessment of ongoing need.
Tips:
- •Cycling isn't strictly evidence-based but is common practice
- •Some people use it only during high-stress periods
- •If thyroid effects concern you, cycling adds a safety margin
What to Expect
Initial effects
Some people notice a calming effect within the first week, especially with Sensoril. Others notice nothing yet. Mild drowsiness is possible initially.
Stress reduction
Most people who respond notice reduced stress reactivity around this time. Stressful situations may feel more manageable. Sleep quality may improve.
Full effects
Hormonal effects (cortisol reduction, testosterone increase) become measurable in studies at this point. Anxiety reduction is typically noticeable. Athletic performance benefits may emerge.
Maintenance
Benefits are maintained with continued use. Consider cycling off every 8-12 weeks to reassess need and prevent tolerance.
Dosing Information
Recommended Dose
300-600mg KSM-66 or 125-250mg Sensoril daily
Range
300-600mg KSM-66 / 125-500mg Sensoril
- •KSM-66: 300mg 1-2x daily with meals
- •Sensoril: 125-250mg once daily, often in evening
- •Higher doses increase risk of side effects without proven additional benefit
Don't exceed recommended doses. Monitor thyroid function if using long-term, especially if you have thyroid concerns.
Practical Details
Timing
KSM-66 can be taken morning and/or evening with food. Sensoril is often taken in the evening due to its more sedating effects. Consistency matters more than timing.
Duration
Best used in cycles: 8-12 weeks on, 2-4 weeks off. Some people use continuously; if so, consider annual thyroid monitoring.
Cost
$15-30/month
Quality KSM-66 or Sensoril products cost $20-30/month. Generic ashwagandha is cheaper but less reliable.
Risks & Considerations
Potential Risks
- •May increase thyroid hormone levels, problematic for hyperthyroidism
- •Rare liver injury reports (causation unclear, but worth monitoring)
- •May cause excessive sedation in some people
- •Quality varies significantly between products
- •May lower blood sugar, monitor if diabetic
Possible Side Effects
- •Drowsiness (especially with Sensoril or high doses)
- •Digestive upset if taken on empty stomach
- •Headache (uncommon)
- •Vivid dreams (some people)
Who Should Avoid This
- •Hyperthyroidism or Graves' disease (may worsen)
- •Pregnancy and breastfeeding (insufficient safety data)
- •Scheduled surgery (stop 2 weeks before)
- •Autoimmune conditions (may stimulate immune system)
- •Taking sedatives or thyroid medications (potential interactions)
Key Research
Ashwagandha reduces cortisol and stress
Journal of the American Nutraceutical Association, 2008
Randomized controlled trial found 125-250mg Sensoril daily reduced cortisol by 14-26% and significantly improved stress assessment scores compared to placebo over 60 days.
View StudyKSM-66 increases testosterone in men
American Journal of Men's Health, 2019
8-week study in overweight men found KSM-66 (600mg/day) increased testosterone by ~15% and improved fatigue, vigor, and sexual well-being compared to placebo.
View StudyAshwagandha for anxiety
Cureus, 2019
Systematic review of 5 RCTs found ashwagandha significantly improved anxiety scores compared to placebo, with effects observed at doses of 300-600mg daily.
View StudyFrequently Asked Questions
KSM-66 vs Sensoril: which should I choose?
KSM-66 is a root-only extract that's more stimulating/energizing, good for stress, testosterone, and athletic performance. Sensoril includes leaf extract, has higher withanolide concentration, and is more sedating, better for anxiety and sleep. If unsure, KSM-66 is more versatile. If anxiety or sleep is your main concern, try Sensoril.
Is ashwagandha safe for long-term use?
Most studies are 8-12 weeks, so long-term data is limited. The main concerns are thyroid effects (may increase T3/T4) and rare liver reports. Conservative approach: cycle on/off (8 weeks on, 2-4 off) and monitor how you feel. Annual thyroid panel is reasonable for continuous users.
Will ashwagandha increase my testosterone?
In men with low-normal testosterone, studies consistently show 10-15% increases over 8-12 weeks. Effects in men with already-optimal testosterone are less clear. It's not a substitute for TRT if you have clinical hypogonadism, but may help optimize levels at the margin.
Can I take ashwagandha with other supplements?
Ashwagandha stacks well with most supplements. Common combinations: ashwagandha + rhodiola for stress, ashwagandha + magnesium for sleep, ashwagandha + creatine for performance. Be cautious combining with other sedating supplements or thyroid-affecting compounds.
Why does ashwagandha make some people tired?
Ashwagandha has GABAergic activity (calming) and may lower cortisol, which can feel sedating, especially in people who are running on stress hormones. If you feel too tired, try taking it at night instead of morning, reduce dose, or switch from Sensoril to the less-sedating KSM-66.
Sources
Related Interventions
Disclaimer: This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider before starting any new health practice or supplement. Evidence levels and recommendations can change, this content was last updated December 2025.