Withanolides (Ashwagandha · Steroidal Lactones · Adaptogen Marker Compound)
| CAS No. | 32911-62-9 (Withanolide A, primary marker) · 5119-48-2 (Withaferin A) |
| Class | Terpenoid · Steroidal Lactone · Ergostane-type C28 Steroid |
| Source | Withania somnifera (Ashwagandha) — root (primary); leaf (secondary, higher withaferin A) |
| Claim strength | High |
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Withania somnifera — ashwagandha, or Indian winter cherry — is among the most extensively documented plants in Ayurvedic medicine, with references in the Charaka Samhita and Sushruta Samhita placing its therapeutic use over 3,000 years ago. The root is classified in Ayurveda as a rasayana — a class of rejuvenating tonics intended to promote longevity, physical vitality, and mental clarity — and as a balya (strength-promoting) and medhya (cognitive-enhancing) herb. The Sanskrit name ashwagandha translates literally as "smell of horse," referencing both the root's characteristic odour and the traditional belief that regular use conferred the strength and virility of a horse. It was prescribed for emaciation, fatigue, sexual debility, memory loss, and as a general restorative across generations of Ayurvedic clinical practice. In Unani medicine, it appears as asgandh and carries similar indications. The plant grows wild across India, the Mediterranean, and parts of Africa — its use in traditional African and North African medicine for inflammation and fever is also documented. The steroidal lactones now identified as withanolides are the molecular explanation for effects that Ayurvedic physicians observed and recorded empirically across three millennia.
Withanolides are a family of over 300 naturally occurring steroidal lactones built on an ergostane C28 skeleton — the marker compound class that defines Withania somnifera (ashwagandha) as an adaptogen and distinguishes genuine root extract from adulterated material. The two most pharmacologically characterised members are Withanolide A (primary adaptogenic and neuroprotective marker) and Withaferin A (anti-inflammatory and immunomodulatory activity). Commercial ashwagandha extract is standardised to total withanolides by HPLC, typically at 2.5%, 5%, or 10% — the percentage reported on the CoA is the quality handle formulators use to align extract dose with clinical reference doses.
Withanolides for Stress Adaptation, Cognitive Function & Physical Performance — Evidence
Adaptogenic activity — HPA axis modulation: Withanolides reduce serum cortisol through modulation of the hypothalamic-pituitary-adrenal axis. Multiple double-blind RCTs document statistically significant reductions in perceived stress scores (PSS) and morning serum cortisol in healthy adults supplemented with standardised Withania somnifera root extract. This is the most commercially robust evidence base for ashwagandha and the primary claim positioning in the global stress and sleep supplement market. Claim strength: High.
Cognitive function and memory: Withanolide A in particular has been shown in preclinical models to promote neurite outgrowth and support acetylcholine signalling. Human RCT data documents improvement in immediate and general memory, executive function, and sustained attention with standardised ashwagandha root extract over 8-week intervention periods. Applicable to nootropic and cognitive ageing formulations. Claim strength: High.
Physical performance and recovery: Controlled trials in resistance-trained adults show meaningful improvements in VO₂ max, muscle strength (bench press, leg extension), and recovery from exercise-induced muscle damage with daily ashwagandha extract supplementation. The mechanism is attributed partly to cortisol attenuation and partly to withanolide-mediated modulation of androgen signalling pathways. Claim strength: High.
Thyroid and testosterone — emerging clinical signals: Preliminary RCT data suggests withanolides may support thyroid hormone levels (T3, T4) in subclinically hypothyroid populations, and serum testosterone in men with below-normal baseline levels. Both signals are mechanistically plausible but require larger, better-powered trials before confident label claim positioning. Claim strength: Moderate.
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Withanolides Dosage, Standardisation & Formulator Specification
Clinically referenced dose: 300–600mg of standardised root extract per day (typically 5% withanolides by HPLC), corresponding to 15–30mg total withanolides daily. Higher-potency extracts (10% withanolides) allow smaller capsule fill weights at equivalent withanolide delivery. The most cited clinical studies use 300mg twice daily of KSM-66 or Sensoril-grade equivalents — when formulating generic standardised extract, align the withanolide mg dose, not the extract mg dose, to the reference study.
Standardisation and CoA verification: Always verify withanolide percentage by HPLC on the CoA — not by gravimetric or UV-spectrophotometric methods, which can overstate withanolide content by including non-withanolide UV-absorbing compounds. Insist on the HPLC method statement in the CoA. The claim "standardised to 5% withanolides" without HPLC confirmation is commercially unverifiable.
Root vs. leaf specification: Root extract is the traditional specification and the substrate for all major clinical trials. Leaf extract produces a different withanolide profile, significantly higher in Withaferin A (which has cytotoxic properties at elevated doses) and lower in Withanolide A. For stress, cognitive, and sports performance positioning, root-only extract is the correct specification. Confirm plant part on the CoA.
Pairs with: Phosphatidylcholine (liposomal ashwagandha for enhanced absorption — growing market segment), Rhodiola rosea (dual-adaptogen stress formulations), L-theanine (stress + cognitive stack), Shilajit (testosterone and vitality positioning), Black pepper extract / Piperine (bioavailability enhancement).
Frequently Asked Questions — Withanolides
What are withanolides and why do they matter for ashwagandha extract quality?
Withanolides are the steroidal lactone compounds that define ashwagandha's pharmacological activity. The withanolide percentage on a CoA is the primary quality indicator for standardised extract — it tells you how much active compound you are actually delivering per capsule. An ashwagandha extract with 2.5% withanolides by HPLC delivers half the active dose of a 5% extract at the same extract weight. Without withanolide standardisation verified by HPLC, dosing consistency across batches cannot be guaranteed.
What is the difference between Withanolide A and Withaferin A?
Both are members of the withanolide class but have distinct activity profiles and tissue distribution. Withanolide A is the primary marker in root extract and is associated with adaptogenic, neuroprotective, and anabolic-supportive activity. Withaferin A is more abundant in leaf material, has documented anti-inflammatory activity, and has also been studied for cytotoxic properties at higher concentrations. Root-only extract standardised to total withanolides (primarily Withanolide A) is the appropriate specification for supplement formulation. Leaf extract or whole-plant extract with high Withaferin A content is a different formulation decision requiring separate safety evaluation.
How do I verify that an ashwagandha CoA is reporting withanolides correctly?
The CoA should state the analytical method as HPLC (high-performance liquid chromatography) with a reference wavelength or gradient programme. UV-spectrophotometric methods are less specific and routinely produce inflated withanolide percentages. The CoA should also confirm plant part (root), species name (Withania somnifera), and extraction solvent (typically hydroethanolic — water/ethanol). If the CoA states only "as per internal standards" without method disclosure, the withanolide claim is unverifiable and the extract should not be used as a reference-dose ingredient.
Is ashwagandha extract safe for long-term daily use?
Standardised Withania somnifera root extract has a well-documented safety profile in clinical trials of up to 8–12 weeks at 300–600mg per day. Long-term data beyond 12 weeks is limited but no serious adverse events have been reported in published trials at these doses. Rare case reports of liver injury have been associated with ashwagandha use — though causality is not established in all cases. Standard supplement label guidance to consult a healthcare provider before use, and avoidance during pregnancy (uterine stimulant activity is documented in traditional medicine), applies. This is not a formulation concern at normal supplement doses but warrants inclusion of appropriate label precautionary text.
Claim-strength scale – High = multiple human studies; Moderate = a few trials; Emerging = early lab data.
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