AdaptogenClinical dose · 300–600mg/day (KSM-66 extract)Onset · Stress and cortisol effects measured at 60 days; memory effects at 8 weeks (MCI trial)

Ashwagandha (KSM-66)

Name: Ashwagandha (KSM-66) — Human Clinical Effect Matrix
Creator: The Nootropic Lab
License: https://creativecommons.org/licenses/by/4.0/

A 2012 RCT in chronically stressed adults (Chandrasekhar et al., KSM-66 600mg/day, 60 days; extract supplied by its maker Ixoreal Biomed) found serum cortisol fell 27.9% versus 7.9% on placebo and perceived stress fell 44%. A 2024 meta-analysis of 9 RCTs confirmed significant reductions in perceived stress, anxiety and cortisol, though a 2019 crossover trial of a low-dose extract in older overweight men found no cortisol effect. A 2017 RCT (Choudhary et al., 300mg twice daily, 8 weeks) improved memory and executive function — in adults with mild cognitive impairment, not healthy adults. Liver-injury case reports exist, and Denmark banned ashwagandha supplements in 2023.

By The Nootropic Lab editorial teamUpdated Oct 14, 20268 min read✓ Fact-checked

Evidence reviewed: Sep 28, 2026

Mechanism of action

Ashwagandha (Withania somnifera) is an Ayurvedic adaptogen. Its withanolides modulate the HPA axis to reduce cortisol, while also inhibiting acetylcholinesterase (preserving acetylcholine) and promoting GABA receptor activity for anxiolytic effects. KSM-66 is a full-spectrum root extract.

Clinical evidence summary

Human effect matrix

Based on human clinical trials only. Animal and in-vitro data excluded.

Effect	Evidence	Magnitude	Studies	Notes
Cortisol Reduction	strong	Large	3	27.9% vs 7.9% serum cortisol drop at 600mg/day (Chandrasekhar 2012) and a significant pooled effect in a 9-RCT meta-analysis; a low-dose crossover trial in older overweight men found no cortisol change, so the effect is dose- and population-dependent.
Anxiety & Stress	strong	Large	2	Perceived stress fell 44% vs 5.5% (Chandrasekhar 2012); the 2024 9-RCT meta-analysis found significant reductions on the Perceived Stress and Hamilton Anxiety scales.
Sleep Quality	moderate	Moderate	—	A 90-day RCT (Gopukumar 2021) reported improved sleep-quality (PSQI) scores; sleep is usually a secondary endpoint.
Memory (Mild Cognitive Impairment)	preliminary	Moderate	1	Choudhary 2017 (n=50, 8 weeks) enrolled adults with mild cognitive impairment; its memory and executive-function gains should not be read as a healthy-adult result.

Evidence key: Strong = multiple consistent RCTs · Moderate = smaller/fewer RCTs · Preliminary = early trials or small n · Mixed = conflicting results

Documented benefits

Cortisol reduction
Lower perceived stress and anxiety
Memory in mild cognitive impairment (one 8-week RCT)
Sleep quality
Muscle strength and recovery

Side effects & cautions

Generally well tolerated in 8–12 week trials
GI upset in some users
Liver injury: published case reports and case series, including cases scored "probable" on the RUCAM causality scale that resolved after stopping — stop and see a doctor if you notice jaundice or dark urine
Denmark banned ashwagandha food supplements in 2023 because a safe dose could not be established
Contraindicated in thyroid conditions
Avoid during pregnancy

How to take

Dosage300–600mg/day (KSM-66)

TimingEvening (1–2 hours before bed) for sleep benefits. Morning for cortisol and stress management. Split dosing (300mg AM + 300mg PM) is the regimen of the Chandrasekhar 2012 and Choudhary 2017 trials (300mg twice daily).

With foodTake with food to minimise GI upset (particularly with 600mg doses). Absorption is not significantly affected by food.

FormsCapsule. Insist on KSM-66 (full-spectrum root extract, 5% withanolides) or Sensoril (leaf + root, 8% withanolides, lower dose needed). Avoid unstandardised ashwagandha with no withanolide percentage stated — active content may be negligible.

Stacking recommendations

Ingredients that pair well with Ashwagandha (KSM-66) and why.

Rhodiola Rosea

The canonical adaptogen duo. Rhodiola is activating (morning); Ashwagandha is calming (evening). Both target HPA axis dysregulation but through different mechanisms and at different times of day — a perfect day/night pair.

L-Theanine

Both reduce anxiety through distinct mechanisms (HPA axis modulation vs. GABA modulation). L-Theanine provides immediate calm; Ashwagandha provides systemic, longer-term stress reduction. Together they work at multiple timescales.

Phosphatidylserine

Both independently reduce cortisol via different pathways (HPA modulation vs. cortisol receptor sensitivity). The combination may provide additive cortisol reduction under high-stress conditions.

Frequently asked questions

KSM-66 vs Sensoril vs generic ashwagandha — which should I choose?

KSM-66 (5% withanolides from root only) is the extract used in the key stress and cognition trials. Sensoril (8% withanolides from root + leaf, lower dose needed at 125–250mg) has good evidence specifically for stress and sleep. Generic ashwagandha without a stated withanolide percentage is unreliable — you may be paying for starchy root powder with minimal active content. Choose KSM-66 or Sensoril.

Will ashwagandha make me tired during the day?

No — at morning doses, most people experience calm focus, not sedation. The tiredness effect is most pronounced when taken at night, where it reduces sleep latency. Ashwagandha doesn't deplete energy; it reduces the cortisol-driven hyperarousal that causes fatigue. Some people find 600mg in the morning slightly sedating — if so, reduce to 300mg or shift to evening only.

Is ashwagandha safe for long-term use?

Long-term data is missing: most trials run 8–12 weeks, and no controlled safety data beyond about 90 days was found. Published case reports link ashwagandha to liver injury (some scored "probable" on the RUCAM causality scale), and Denmark banned ashwagandha food supplements in 2023 because a safe dose could not be established. Stop and see a doctor if you develop jaundice or dark urine. Avoid if you have thyroid conditions (autoimmune thyroid disease) as withanolides can modulate thyroid hormone levels.

Can ashwagandha increase testosterone?

Two RCTs found increases: 600mg/day for 8 weeks in young men starting resistance training raised testosterone alongside greater strength gains (2015), and a crossover trial in overweight men aged 40–70 found testosterone +14.7% and DHEA-S +18% versus placebo — but no change in cortisol, fatigue or vigour (Lopresti 2019). The magnitude varies by population and extract.

Top stacks containing Ashwagandha (KSM-66)

Hunter Focus

6.3/10

Roar Ambition