Ashwagandha (Withania somnifera)
The premier adaptogen for stress, cortisol, and hormonal balance
Also known as: Withania somnifera • Indian Ginseng • Winter Cherry
Overview
Ashwagandha (Withania somnifera) is one of the most important herbs in Ayurvedic medicine, where it has been used for over 3,000 years as a rasayana (rejuvenating tonic). Classified as an adaptogen, ashwagandha helps the body resist and adapt to physical and mental stressors by modulating the hypothalamic-pituitary-adrenal (HPA) axis. Its primary active compounds, withanolides, have been shown to reduce cortisol levels by 11–32% in clinical trials, making it one of the most effective natural stress-management tools available. Beyond stress reduction, ashwagandha has demonstrated significant benefits for anxiety, sleep quality, testosterone levels in men, thyroid function, exercise performance, and cognitive function. The two most studied standardized extracts are KSM-66 (full-spectrum root extract) and Sensoril (root and leaf extract), both of which have robust clinical evidence supporting their efficacy.
Key Benefits
Cortisol & Stress Reduction
Ashwagandha is one of the most effective natural cortisol-lowering agents studied. A landmark 60-day RCT found that 300 mg of KSM-66 twice daily reduced serum cortisol by 27.9% compared to placebo. Participants also reported 44% reductions in perceived stress scores.
Anxiety Relief
Multiple clinical trials demonstrate significant anxiolytic effects. A systematic review of 5 RCTs found that ashwagandha significantly reduced anxiety scores on the Hamilton Anxiety Rating Scale, with effects comparable to some pharmaceutical anxiolytics but without the side effects or dependency risk.
Sleep Quality
Ashwagandha improves sleep quality through multiple mechanisms: cortisol reduction, GABAergic activity, and its species name 'somnifera' literally means 'sleep-inducing.' Clinical trials show improvements in sleep onset latency, total sleep time, and sleep quality scores, particularly with the triethylene glycol compound found in leaf extracts.
Testosterone & Male Fertility
In men, ashwagandha has been shown to increase testosterone levels by 10–22% in multiple studies. It also significantly improves sperm count, motility, and semen quality. A 90-day study in infertile men found a 167% increase in sperm count and 53% increase in semen volume.
Exercise Performance
Ashwagandha enhances both strength and cardiorespiratory endurance. Studies show increases in VO2 max (by 4.9–12%), bench press and leg extension strength, muscle size, and faster recovery. It also reduces exercise-induced muscle damage markers.
Cognitive Function
Ashwagandha improves attention, information processing speed, and memory. Its neuroprotective effects include promoting nerve growth factor (NGF) production and protecting against oxidative stress in the brain. Benefits are seen in both healthy adults and those with mild cognitive impairment.
Dosage & How to Take
The standard dose is 300–600 mg of a standardized extract (KSM-66 or Sensoril) daily. KSM-66 is typically dosed at 300 mg twice daily or 600 mg once daily. Sensoril is typically dosed at 125–250 mg once or twice daily due to its higher withanolide concentration.
| Purpose | Dose | Notes |
|---|---|---|
| Stress & anxiety | 300 mg KSM-66 twice daily | Most studied protocol for cortisol reduction |
| Sleep improvement | 300–600 mg before bed | Sensoril or KSM-66; leaf extract may be more sedating |
| Testosterone support | 600 mg KSM-66 daily | Studies used 8–12 week protocols |
| Exercise performance | 300–600 mg daily | Take consistently; benefits build over 8+ weeks |
| General adaptogenic support | 300 mg daily | Minimum effective dose for most benefits |
Best Time to Take
For stress/energy: take in the morning. For sleep: take 30–60 minutes before bed. Can be split into morning and evening doses for all-day adaptogenic support.
With or Without Food
Best taken with food to improve absorption and reduce potential stomach discomfort. Fat-containing meals may enhance absorption of fat-soluble withanolides.
Forms & Bioavailability
| Form | Absorption | Best For | Notes |
|---|---|---|---|
| KSM-66 (Root Extract) | High | Stress, testosterone, performance, cognition | Full-spectrum root extract standardized to 5% withanolides. Most clinical evidence. |
| Sensoril (Root + Leaf) | High | Anxiety, sleep, cortisol reduction | Higher withanolide concentration (10%). May be more calming/sedating. |
| Generic Root Powder | Lower | Budget option, traditional use | Less standardized. Requires higher doses (1–6 g) for equivalent effects. |
| Shoden (Leaf Extract) | High | Sleep, relaxation | Standardized to 35% withanolide glycosides. Newer extract with strong sleep data. |
Side Effects & Safety
Common
- Generally well-tolerated
- Mild drowsiness (especially at higher doses)
- Mild GI discomfort in some individuals
Rare
- Thyroid hormone elevation (may be beneficial or problematic depending on thyroid status)
- Headache
- Vivid dreams
Contraindications
- Hyperthyroidism (ashwagandha may increase thyroid hormones)
- Autoimmune conditions (may stimulate immune system)
- Pregnancy (traditionally contraindicated)
- Surgery (discontinue 2 weeks before due to potential sedative interactions)
Interactions
Ashwagandha may increase thyroid hormone levels. Those on thyroid medication should monitor levels closely.
May enhance sedative effects. Use caution and start with lower doses.
Ashwagandha may stimulate immune function, potentially counteracting immunosuppressive drugs.
May lower blood sugar. Monitor glucose levels if taking diabetes medications.
Scientific Research
Ashwagandha and Cortisol Reduction
60-day RCT found that 300 mg KSM-66 twice daily reduced serum cortisol by 27.9% and perceived stress by 44% compared to placebo.
Ashwagandha and Anxiety
Systematic review of 5 RCTs concluded that ashwagandha significantly reduced anxiety scores compared to placebo, with a large effect size (d = 1.56).
Ashwagandha and Testosterone
8-week study in healthy men found that 600 mg KSM-66 daily increased testosterone by 17% and DHEA-S by 18%, while reducing cortisol by 11%.
Ashwagandha and Sleep
Double-blind RCT found that 600 mg ashwagandha root extract significantly improved sleep quality (72% improvement vs. 29% in placebo), sleep onset latency, and mental alertness upon waking.
Food Sources
Frequently Asked Questions
Medical Disclaimer
This content is for educational and informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional before starting any supplement regimen, especially if you have pre-existing health conditions or are taking medications. The statements on this page have not been evaluated by the Food and Drug Administration.