Ashwagandha (KSM-66)
Ashwagandha (Withania somnifera) reduces cortisol by 25–30% and raises testosterone in RCTs. KSM-66 vs Sensoril extract comparison, 300–600mg dosing, and what labs to run before and after.
What is Ashwagandha?
Ashwagandha (Withania somnifera) is a root herb native to India, North Africa, and the Mediterranean. Known in Ayurveda as the premier rasayana (rejuvenating herb) and a foundational adaptogen, it has been used for over 3,000 years. Its active compounds — withanolides (steroidal lactones) — are responsible for the majority of its documented physiological effects.
Modern supplement forms use standardised root extracts to guarantee withanolide content. The two leading standardised extracts — KSM-66 (Ixoreal Biomed, India) and Sensoril (Natreon, India) — are both backed by multiple clinical trials.
Mechanism of Action — HPA Axis Modulation
Ashwagandha acts primarily on the hypothalamic-pituitary-adrenal (HPA) axis — the central stress response system. Under chronic stress, the HPA axis becomes dysregulated, leading to elevated cortisol, disrupted sleep, and downstream hormonal consequences including testosterone suppression.
Withanolides modulate key nodes in this pathway:
- Reduce CRH (corticotropin-releasing hormone) signalling from the hypothalamus
- Decrease ACTH (adrenocorticotropic hormone) from the pituitary
- Lower cortisol output from the adrenal glands
- GABA-mimetic activity — withanolides interact with GABA-A receptors, contributing to anxiolytic and sleep-promoting effects
The testosterone increase is likely secondary to cortisol reduction — cortisol competes with testosterone for the same precursor cholesterol via cortisol-testosterone see-saw, and high cortisol directly inhibits Leydig cell testosterone synthesis.
Evidence & Research
Ashwagandha has an unusually strong clinical evidence base for an adaptogen:
- Cortisol: The landmark KSM-66 RCT (Chandrasekhar et al., 2012) showed a 27.9% reduction in morning serum cortisol vs 7.9% in placebo at 60 days using 300mg twice daily
- Stress/anxiety: Standardised PSS (Perceived Stress Scale) and GAD scores show 30–40% improvement vs placebo in most RCTs
- Testosterone: 300mg twice daily in infertile men showed +17% serum testosterone at 90 days (Mahdi et al., 2009). A second RCT in resistance-trained men showed significant testosterone increase with 600mg/day
- Sleep quality: WASO (wake after sleep onset) and total sleep time both improve significantly — one RCT showed 1.5× improvement in sleep quality scores
- Physical performance: KSM-66 studies in athletes show VO2 max improvements and better muscle recovery
Use KSM-66 at 300mg twice daily (morning and evening) for cortisol and testosterone optimisation. For sleep primarily, 600mg before bed is a valid alternative. Run baseline morning cortisol and testosterone before starting, retest at 90 days.
KSM-66 vs Sensoril — Extract Comparison
Both extracts are made by Indian companies from Indian-grown Withania somnifera, but their processing and target effects differ meaningfully:
| Parameter | KSM-66 | Sensoril |
|---|---|---|
| Plant part | Root only | Root + leaf |
| Withanolide content | ≥5% withanolides | ≥10% withanolide glycosides |
| Best for | Testosterone, performance, thyroid support, cortisol | Stress, anxiety, sleep, cognitive function |
| Typical dose | 300mg twice daily (600mg/day) | 125–250mg twice daily |
| RCT count | 20+ studies | 12+ studies |
| Stimulating vs calming | Slightly more energising | Slightly more sedating |
| India availability | Widely available; many Indian brands | Available; often in imported products |
Testosterone Connection
The testosterone evidence is specific to men and most pronounced in those with stress-elevated cortisol or fertility issues. The mechanism is primarily indirect — by reducing cortisol, ashwagandha removes the hormonal suppression of testosterone synthesis.
For men with genuinely low testosterone due to primary hypogonadism (testicular dysfunction) rather than HPA dysregulation, ashwagandha's effect will be smaller. The greatest responders are men with:
- High-stress jobs with chronically elevated cortisol
- Poor sleep quality
- Overtraining without adequate recovery
- Subfertility or suboptimal sperm parameters
Sleep Quality Evidence
Ashwagandha improves sleep through GABA receptor modulation (withanolide interactions) and cortisol reduction. Key metrics improved in RCTs include:
- Sleep latency (time to fall asleep): reduced
- WASO (wake after sleep onset): reduced
- Total sleep time: modestly increased
- Non-restorative sleep: improved in chronic insomnia populations
Cycling, Timing & Drug Interactions
Cycling: Most practitioners recommend 8–12 weeks on, 4 weeks off, though this is based on traditional use rather than strong clinical data. Some individuals use it year-round without apparent issues.
Timing: Take in the morning for cortisol regulation and daytime stress resilience. Take 1–2 hours before bed for sleep improvement. If taking twice daily, morning + evening split serves both goals.
Thyroid considerations: Ashwagandha can raise thyroid hormone levels (T3, T4) and TSH in some individuals. If you are on thyroid medication (levothyroxine, T3), monitor TSH and T4 closely. Space ashwagandha and thyroid medication by at least 2 hours.
What labs to run: Before starting: morning serum cortisol (8–9am), total testosterone, TSH, free T3/T4. Retest at 90 days.
Frequently Asked Questions
Does ashwagandha increase testosterone?
Yes, in clinical trials with KSM-66 extract. A double-blind RCT in infertile men showed +17% serum testosterone at 90 days on 300mg twice daily. Effects are most pronounced in men with stress-related hormonal suppression. Cortisol directly suppresses testosterone synthesis, so reducing cortisol via ashwagandha raises testosterone indirectly.
KSM-66 vs Sensoril — which is better?
Both are high-quality extracts. KSM-66 (root only, ≥5% withanolides) is better studied for performance, testosterone, and energy. Sensoril (root + leaf, higher withanolide glycosides) is generally preferred for stress and sleep. For active urban professionals targeting cortisol and testosterone, KSM-66 at 600mg/day is the evidence-based choice.
When should I take ashwagandha for cortisol?
Cortisol is highest in the morning (cortisol awakening response). Take one dose in the morning to blunt the cortisol peak. If taking twice daily, add an evening dose. Consistency across weeks matters more than precise daily timing.
How long before ashwagandha works for stress?
Most RCTs show statistically significant cortisol and stress score reductions at 60–90 days. Some people notice sleep improvement within 2–4 weeks. The full measurable effect on morning serum cortisol typically emerges at 8–12 weeks of consistent dosing.