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evidence · mechanism · dose
Supplements/Herb

Ashwagandha

aka Withania somnifera · Indian Ginseng · KSM-66 · Shoden

Adaptogenic herb that down-regulates HPA-axis output — lowers cortisol, supports T in stressed men.

Cortisol ManagementTestosterone SupportSleep & RecoveryMood & AnxietyMuscle Growth

Overview

An evergreen shrub in the nightshade family used for >3,000 years in Ayurveda. Standardized root extracts (KSM-66, Shoden) deliver withanolide-rich doses studied in modern trials.

Natural sources
  • Root extract (most studied)
  • Leaf extract (different alkaloid profile)
Common forms
  • KSM-66 (5% withanolides, root-only)
  • Shoden (35% withanolides)
  • Sensoril (10% withanolides, leaf + root)

Forms & variants of Ashwagandha

Different chemical forms of Ashwagandha behave differently. Browse each form's mechanism, bioavailability, and best-use context.

KSM-66 (root extract)
KSM-66 Ashwagandha

Root-only standardized ashwagandha extract — the most-studied form for stress and T-support.

Sensoril (root + leaf)
Sensoril Ashwagandha

Root + leaf extract standardized to ≥10% withanolides — higher potency, more sedating.

Strength protocol (600 mg)
Ashwagandha (Strength)

KSM-66 dose for resistance training adaptations.

Mechanism of action

Withanolides modulate the HPA axis, attenuating cortisol secretion under stress. Likely acts on GABA-A receptors and reduces sympathetic tone.

Pathways
  • · HPA-axis modulation
  • · GABA-A agonism
  • · Nrf2 antioxidant pathway
Hormones
  • · Cortisol (↓)
  • · DHEA (↑)
  • · Testosterone (↑ in subfertile/stressed men)
  • · TSH (↑ mildly)
Neurotransmitters
  • · GABA (↑)
  • · Serotonin (modulates)

Effects on the body

Decreases
Cortisol (~20–30%)
Decreases
Perceived stress
Increases
Testosterone in stressed/subfertile men
Increases
VO₂ max
Supports
Sleep quality

Organ system effects

Brain & CNS

Anxiolytic via GABA-A; reduces sympathetic output.

Endocrine

Lowers cortisol; raises T 10–20% in stressed/subfertile men.

Reproductive

Improves sperm count, motility, morphology in infertile men.

Immune System

Modulates NK cell activity.

Evidence-based benefits

Reduces perceived stress and serum cortisol

Strong evidence

Improves sleep quality (PSQI)

Moderate evidence

Increases testosterone in stressed/subfertile men

Moderate evidence

Improves strength and recovery with resistance training

Moderate evidence

Reduces symptoms of anxiety

Moderate evidence

Potential side effects

Common
  • · Drowsiness (especially at higher doses)
  • · Mild GI upset
Rare
  • · Headache
  • · Hyperthyroidism (rare; possible TSH elevation)
Serious
  • · Rare reports of acute liver injury — discontinue if jaundice develops

Drug interactions

Thyroid medications
May potentiate thyroid hormone activity.
moderate
Immunosuppressants
Immunomodulatory — may interfere.
moderate
Sedatives / benzodiazepines
Additive CNS depression.
moderate
Anti-diabetic drugs
May lower blood sugar additively.
minor

Safety & non-supplemental interactions

Educational summary — always confirm with your clinician or pharmacist before starting, stopping, or combining with prescription therapy.

Avoid if you are
  • ·Pregnant or breastfeeding (insufficient safety data)
  • ·Children under 18 (unless directed by a clinician)
  • ·Pregnant (abortifacient in animal studies)
  • ·Breastfeeding
Avoid with these conditions
  • ·Hormone-sensitive cancers (breast, prostate, ovarian, uterine)
  • ·Autoimmune disease (lupus, MS, RA, Hashimoto's)
  • ·Hyperthyroidism
  • ·Active liver disease — rare hepatotoxicity reported
  • ·Hormone-sensitive prostate cancer
Avoid / monitor with these medications
  • ·Hormonal contraceptives, HRT, tamoxifen, aromatase inhibitors
  • ·Alcohol, benzodiazepines, opioids, sedating antihistamines (additive CNS depression)
  • ·Thyroid hormone (levothyroxine) — may push toward hyperthyroid
  • ·Immunosuppressants
  • ·Sedatives / benzodiazepines / alcohol
  • ·Antihypertensives
  • ·Antidiabetic drugs (additive hypoglycemia)
Before surgery
  • ·Discontinue ≥2 weeks before surgery — CNS depressant effects may compound anesthesia.

Supplement interactions

Pairs well with
  • Magnesium glycinate
    Synergistic for sleep and stress.
  • L-Theanine
    Complementary GABAergic calm without sedation.
Avoid combining with
  • Other strong sedatives
    Additive drowsiness.

Dosing & bioavailability

Typical dose
600 mg KSM-66 (or 240 mg Shoden)
Beginner dose
300 mg KSM-66
Study range
300–675 mg/day root extract
Upper safe limit
Not formally defined; >1,000 mg/day not better in trials
Best form
KSM-66 root extract, standardized to ≥5% withanolides
Timing
Split AM/PM, or single dose evening for sleep
With food?
With food to reduce GI upset

Where to buy

Affiliate-style search links to reputable retailers. We don't endorse specific brands — verify third-party testing (USP, NSF, Informed Sport) before purchase.

Herb
Ashwagandha
Amazon
Wide selection · fast shipping
Herb
Ashwagandha
iHerb
Global delivery · curated brands
Herb
Ashwagandha
Thorne
Practitioner-grade · NSF tested

Scientific evidence (11)

RCTIndian J Psychol Med · 2012

Examining the effect of Withania somnifera supplementation on stress and anxiety

Chandrasekhar K, Kapoor J, Anishetty S

Double-blind RCT, 64 adults with chronic stress, 300 mg KSM-66 BID × 60 days.

Key findings

Cortisol reduced 27.9% vs placebo; significant improvements on PSS, GHQ, DASS scales.

Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — Reduces perceived stress and serum cortisol

Live PubMed search

Live results for "Ashwagandha Reduces perceived stress and serum cortisol" across the PubMed/MEDLINE peer-reviewed index.

Key findings

Opens current human and preclinical literature matching Ashwagandha and "Reduces perceived stress and serum cortisol". Filter by RCT, meta-analysis, or year on the results page.

Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — Improves sleep quality

Live PubMed search

Live results for "Ashwagandha Improves sleep quality" across the PubMed/MEDLINE peer-reviewed index.

Key findings

Opens current human and preclinical literature matching Ashwagandha and "Improves sleep quality". Filter by RCT, meta-analysis, or year on the results page.

Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — Increases testosterone in stressed/subfertile men

Live PubMed search

Live results for "Ashwagandha Increases testosterone in stressed/subfertile men" across the PubMed/MEDLINE peer-reviewed index.

Key findings

Opens current human and preclinical literature matching Ashwagandha and "Increases testosterone in stressed/subfertile men". Filter by RCT, meta-analysis, or year on the results page.

Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — Improves strength and recovery with resistance training

Live PubMed search

Live results for "Ashwagandha Improves strength and recovery with resistance training" across the PubMed/MEDLINE peer-reviewed index.

Key findings

Opens current human and preclinical literature matching Ashwagandha and "Improves strength and recovery with resistance training". Filter by RCT, meta-analysis, or year on the results page.

Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — randomized controlled trial

Live PubMed search

Live results for "Ashwagandha randomized controlled trial" across the PubMed/MEDLINE peer-reviewed index.

Key findings

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Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — meta-analysis

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Live results for "Ashwagandha meta-analysis" across the PubMed/MEDLINE peer-reviewed index.

Key findings

Opens current human and preclinical literature matching Ashwagandha and "meta-analysis". Filter by RCT, meta-analysis, or year on the results page.

Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — pharmacokinetics

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Key findings

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Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — safety adverse events

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Live results for "Ashwagandha safety adverse events" across the PubMed/MEDLINE peer-reviewed index.

Key findings

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Open study
Systematic reviewPubMed (NLM) · 1970

PubMed: Ashwagandha — dose response

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Live results for "Ashwagandha dose response" across the PubMed/MEDLINE peer-reviewed index.

Key findings

Opens current human and preclinical literature matching Ashwagandha and "dose response". Filter by RCT, meta-analysis, or year on the results page.

Open study
Systematic reviewGoogle Scholar · 1970

Google Scholar: Ashwagandha — clinical evidence

Live Scholar search

Cross-database citation index for Ashwagandha as it relates to "clinical evidence".

Key findings

Includes preprints, theses, and journal articles. Useful for tracking citation counts and follow-on work.

Open study
Educational use only. This profile is not medical advice. Consult a qualified healthcare professional before starting any supplement, especially if you take prescription medication or have a chronic condition.