Withanolide A

Withanolide A at a Glance

Withanolide A is a C28 steroidal lactone (withanolide) from the root of ashwagandha (Withania somnifera), and one of the plant’s principal anti-stress, neuroactive constituents. Where its famous sibling withaferin A is a reactive, cytotoxic electrophile studied mostly as an anticancer agent, withanolide A is the neurotrophic withanolide — the molecule associated with rebuilding neurons rather than killing them.

Its signature finding is neuroregeneration: in cultured neurons, withanolide A promotes neurite outgrowth, regenerates damaged axons and dendrites, and reconstructs synapses — even after the network has been degraded ^{1,2,3,4Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →Reference 3Zhao J et al. · 2002Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activitiesView study →Reference 4Tohda C et al. · 2005Search for natural products related to regeneration of the neuronal networkView study →}. Alongside this sit anxiolytic/anti-stress and neuroprotective signals, proposed to run through GABAergic and HPA-axis (stress-hormone) mediation ^{8,9Reference 8Bhattacharya SK et al. · 2000Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental studyView study →Reference 9Candelario M et al. · 2015Direct evidence for GABAergic activity of Withania somnifera on mammalian ionotropic GABA-A and GABA-ρ receptorsView study →}.

The honest posture up front: the evidence is preclinical — cultured neurons and rodent models — and much of the anxiolytic data belongs to the glycowithanolide fraction or whole extract, not the isolated molecule. There are no isolated-molecule human trials, and oral bioavailability of the molecule is modest ^{11Reference 11Patil D et al. · 2013AnimalDetermination of withaferin A and withanolide A in mice plasma using HPLC-tandem mass spectrometry: application to pharmacokinetics after oral administration of Withania somnifera aqueous extractView study →}. As a compound it appears low-toxicity — non-cytotoxic to neurons, indeed neuroprotective ^{7Reference 7Dar NJ et al. · 2025Withaferin-A kills neuronal cells: an off-putting facet of Withania somnifera as a neuroprotectantView study →} — but no isolated-molecule human safety dataset exists to anchor that firmly.

Neuroregeneration — The Neurotrophic Withanolide

This is the point of the page. Most natural “neuroprotectants” only shield neurons from further damage; withanolide A is unusual in that the isolated molecule promotes active regrowth of already-damaged neuronal structures.

The defining series comes from Kuboyama, Tohda and Komatsu. In cultured cortical and neuroblastoma neurons, withanolide A induced significant neurite outgrowth at low-micromolar concentrations (~1 µM) ^{3Reference 3Zhao J et al. · 2002Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activitiesView study →}. When neurons were exposed to different Ashwagandha constituents, withanolide A produced axon-predominant outgrowth, while the related withanosides drove dendrite-predominant outgrowth — a genuine structural specificity, not just generic “growth” ^{2Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →}. The landmark 2005 paper went further: withanolide A regenerated both axons and dendrites and reconstructed synapses in neurons that had already been damaged, i.e. it acted on a degenerated network rather than merely a healthy one ^{1Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →}.

Mechanistically, later work profiled withanolide A against neurodegenerative targets and found it reverses the neurite-outgrowth inhibition caused by dexamethasone — implicating a glucocorticoid/stress-hormone axis in its neurotrophic action, and tying the neuroregeneration story back to the adaptogenic, anti-stress framing of the whole herb ^{5Reference 5Crane EA et al. · 2019Profiling withanolide A for therapeutic targets in neurodegenerative diseasesView study →}. A related withanoside (withanoside IV) and its active metabolite sominone independently rescued memory and prevented neuronal loss in amyloid-β mouse models when given orally — the in-vivo bookend to the in-vitro withanolide A data ^{6Reference 6Kuboyama T et al. · 2006Withanoside IV and its active metabolite, sominone, attenuate Aβ(25-35)-induced neurodegenerationView study →}.

The caveat that keeps this honest: essentially all of this is cultured-neuron and rodent work. Withanolide A has never been tested as an isolated molecule in a human neuroregeneration trial, and the molecule’s own oral pharmacokinetics are modest ^{11Reference 11Patil D et al. · 2013AnimalDetermination of withaferin A and withanolide A in mice plasma using HPLC-tandem mass spectrometry: application to pharmacokinetics after oral administration of Withania somnifera aqueous extractView study →}. The signal is mechanistically striking; the clinical proof does not yet exist.

Withanolide A vs. Withaferin A

The two headline withanolides of ashwagandha point in opposite pharmacological directions, and conflating them is the most common error about this chemistry.

• Withaferin A carries an α,β-unsaturated (reactive) lactone that acts as a Michael acceptor, covalently modifying protein cysteines. That reactivity makes it a broad-spectrum, cytotoxic molecule — the anticancer withanolide — and a 2025 study bluntly titled its effect on neurons “an off-putting facet,” showing withaferin A kills differentiated neuronal cells through ROS-driven mitochondrial dysfunction and apoptosis ^{7Reference 7Dar NJ et al. · 2025Withaferin-A kills neuronal cells: an off-putting facet of Withania somnifera as a neuroprotectantView study →}.
• Withanolide A lacks that promiscuous electrophilic reactivity in the same way, and the same research lineage identifies it (with withanone) as neuroprotective — the molecule that regenerates neurons ^{1,2,7Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →Reference 7Dar NJ et al. · 2025Withaferin-A kills neuronal cells: an off-putting facet of Withania somnifera as a neuroprotectantView study →}.

There is also a tissue split that matters for real-world exposure: withaferin A concentrates in the leaf and in withaferin-A-rich chemotypes, whereas withanolide A is more root-associated — and the root is the part used in essentially all traditional preparations and human trials. So the withanolide most people actually ingest from root ashwagandha is skewed toward the neurotrophic, not the cytotoxic, member.

What It's Used For

Beyond the neuroregeneration signature, withanolide A’s pharmacology spans anxiolytic/anti-stress, neuroprotective and immunomodulatory activity. The evidence splits sharply by whether the isolated molecule — rather than the glycowithanolide fraction or whole extract — was the thing tested.

Evidence by IndicationStrength of support · Beta

Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. Every application here is preclinical, so scores reflect mechanistic depth and consistency, not clinical proof, and stay modest by design. Each application links to its write-up.

01Neuroregeneration (neurite outgrowth)Promising52%Convergent isolate-level in-vitro neuron work + target profiling ^{1,2,3,5Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →Reference 3Zhao J et al. · 2002Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activitiesView study →Reference 5Crane EA et al. · 2019Profiling withanolide A for therapeutic targets in neurodegenerative diseasesView study →}

02Anxiolytic / anti-stressShaky34%Glycowithanolide-fraction + extract behavioural/GABAergic models ^{8,9Reference 8Bhattacharya SK et al. · 2000Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental studyView study →Reference 9Candelario M et al. · 2015Direct evidence for GABAergic activity of Withania somnifera on mammalian ionotropic GABA-A and GABA-ρ receptorsView study →}

03NeuroprotectionShaky30%Isolate identified as neuroprotective; neurodegeneration target profiling ^{5,6,7Reference 5Crane EA et al. · 2019Profiling withanolide A for therapeutic targets in neurodegenerative diseasesView study →Reference 6Kuboyama T et al. · 2006Withanoside IV and its active metabolite, sominone, attenuate Aβ(25-35)-induced neurodegenerationView study →Reference 7Dar NJ et al. · 2025Withaferin-A kills neuronal cells: an off-putting facet of Withania somnifera as a neuroprotectantView study →}

04Immunomodulatory (Th1)Shaky20%One isolate-in-splenocyte + extract-in-mouse study ^{10Reference 10Malik F et al. · 2007AnimalA standardized root extract of Withania somnifera and its major constituent withanolide-A elicit humoral and cell-mediated immune responses by up regulation of Th1-dominant polarization in BALB/c miceView study →}

Mechanisms

Unifying reading: withanolide A is a non-electrophilic, neurotrophic withanolide — its defining action is promoting structural neuronal repair, with a glucocorticoid/stress-axis link that dovetails with ashwagandha’s adaptogenic anti-stress profile. This is the mechanistic opposite of withaferin A’s reactive cytotoxicity.

Pharmacokinetics

The value-add caveat. In mice given oral W. somnifera aqueous extract, withanolide A was rapidly absorbed but had only ~two-thirds the relative oral bioavailability of withaferin A (withaferin A showed ~1.5× the relative bioavailability of withanolide A) ^{11Reference 11Patil D et al. · 2013AnimalDetermination of withaferin A and withanolide A in mice plasma using HPLC-tandem mass spectrometry: application to pharmacokinetics after oral administration of Withania somnifera aqueous extractView study →} — i.e. modest oral exposure. No validated human pharmacokinetics exist, and brain penetration after oral dosing is not quantified, which is the key unknown for a molecule whose headline effects are all central-nervous-system regeneration observed in vitro. The persistent tension here is that the striking neurotrophic data are cell-culture concentrations (~1 µM), while the achievable oral exposure of the isolated molecule in a living animal — let alone a human brain — is unestablished.

Clinical Trials

There is no published human efficacy trial of purified withanolide A for any indication. Human ashwagandha trials test standardized root extracts (e.g. KSM-66, Sensoril/Shoden) — for stress, anxiety, sleep and related outcomes ^{12Reference 12Chandrasekhar K et al. · 2012RCTA prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adultsView study →} — and their results cannot be attributed to withanolide A specifically, since the extracts are complex mixtures of withanolides, withanosides and glycowithanolides. The entire efficacy literature for the isolated molecule is preclinical.

Last checked: July 2026.

Isolate vs. Plant Studies

Withanolide A sits in an unusual middle. Its neuroregeneration evidence is genuinely isolate-level — the Kuboyama/Tohda cell studies dosed the purified molecule and saw axon/dendrite/synapse effects ^{1,2,3Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →Reference 3Zhao J et al. · 2002Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activitiesView study →}, and the immune study tested the isolate in splenocytes ^{10Reference 10Malik F et al. · 2007AnimalA standardized root extract of Withania somnifera and its major constituent withanolide-A elicit humoral and cell-mediated immune responses by up regulation of Th1-dominant polarization in BALB/c miceView study →}. That is a real strength for the mechanism. But its anxiolytic/anti-stress reputation is fraction- or extract-level: the lorazepam-comparable anxiolysis was shown for the glycowithanolide fraction ^{8Reference 8Bhattacharya SK et al. · 2000Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental studyView study →}, and the GABAergic mechanism for whole extract ^{9Reference 9Candelario M et al. · 2015Direct evidence for GABAergic activity of Withania somnifera on mammalian ionotropic GABA-A and GABA-ρ receptorsView study →}. And every human outcome for ashwagandha belongs to standardized root extracts ^{12Reference 12Chandrasekhar K et al. · 2012RCTA prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adultsView study →}, not to this molecule. So the transferability caveat runs both ways: the in-vitro regeneration is convincingly the molecule’s own, while the calming/sleep and clinical stories are the plant’s, with withanolide A only one plausible contributor.

Prevalence in Nature

Withanolide A is a characteristic withanolide of ashwagandha (Withania somnifera), most associated with the root — the part used in traditional preparations and nearly all clinical research. It is one member of a large family: standardized root extracts are typically standardized to total withanolides (~1.5–5%) ^{12Reference 12Chandrasekhar K et al. · 2012RCTA prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adultsView study →}, within which withanolide A is a minor individual fraction rather than the dominant single compound. Content varies markedly with chemotype, plant part, extract type and standardization target — a recurring theme in the ashwagandha literature, where Indian germplasm splits into withaferin-A-rich and withanolide-rich chemotypes. Notably, the root/leaf split tilts withanolide A toward the root and withaferin A toward the leaf, so root-based products are relatively enriched in the neurotrophic member. Withanolides as a class are otherwise distributed across several Solanaceae genera, but withanolide A itself is reported chiefly from Withania.

A precise, separately-quantified withanolide-A percentage for defined root material is not well documented in the sources reviewed — see the gaps tracker.

Discovery & Synthesis

The withanolides — C28 steroidal lactones built on an ergostane skeleton with a characteristic δ-lactone side chain — were first characterized by David Lavie, Erwin Glotter and Yaffa Kirson at the Weizmann Institute of Science beginning in 1965, with withaferin A as the founding, name-giving member of the class. Withanolide A was described among the Withania somnifera root withanolides in the years that followed, as the class was systematically catalogued (the “withanolide A/B/…” naming convention dates from that structural work). Its neuroactivity was not appreciated until the Kuboyama/Tohda neurite-outgrowth studies of the early 2000s ^{1,2,3Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →Reference 3Zhao J et al. · 2002Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activitiesView study →} recast it from a catalogued steroidal lactone into “the neurotrophic withanolide.”

Manufacture today is by extraction from ashwagandha root (or, for research quantities, chromatographic isolation from root extract); withanolide A is used essentially as a research reference compound and analytical marker rather than a bulk commercial ingredient — commercial ashwagandha products are standardized to total withanolides, not to isolated withanolide A. No widely used total synthesis is established as the production route.

Patents: not yet researched.

Toxicity & Safety

Withanolide A carries a low flag — and the reasoning is the mirror image of its sibling’s. Unlike withaferin A (flagged moderate for reactive, cytotoxic electrophilic chemistry), withanolide A is non-cytotoxic to neurons and is repeatedly described as neuroprotective/neurotrophic ^{1,7Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 7Dar NJ et al. · 2025Withaferin-A kills neuronal cells: an off-putting facet of Withania somnifera as a neuroprotectantView study →}; it lacks the promiscuous Michael-acceptor reactivity that drives withaferin A’s off-target liability. That said, the low flag rests on preclinical data only — there is no isolated-molecule human toxicity dataset, so “low” reflects an absence of cytotoxic signal plus the molecule’s regenerative profile, not a completed human safety package. Reported interactions are theoretical and mechanism-derived: possible additive effects with sedative/GABAergic agents (from the extract’s GABA-A/GABA-ρ activity) ^{9Reference 9Candelario M et al. · 2015Direct evidence for GABAergic activity of Withania somnifera on mammalian ionotropic GABA-A and GABA-ρ receptorsView study →}, and immune-modulating (Th1-skewing) effects that are worth noting alongside immunosuppressant or autoimmune contexts ^{10Reference 10Malik F et al. · 2007AnimalA standardized root extract of Withania somnifera and its major constituent withanolide-A elicit humoral and cell-mediated immune responses by up regulation of Th1-dominant polarization in BALB/c miceView study →}. At the herb level, ashwagandha itself is traditionally avoided in pregnancy (a long-standing precaution reflected in traditional use and modern herb monographs) — but pregnancy/lactation is a whole-herb decision made on the ashwagandha page where intake is decided, not a property established for this isolated molecule.

Safety at a Glance

✅ Low / no toxicity

• Non-cytotoxic, neurotrophic profile. In neuronal studies withanolide A promotes regeneration rather than causing cell death — the opposite of withaferin A.
• No isolate cytotoxicity signal. No reactive-electrophile liability of the kind that flags its sibling withanolide.
• Preclinical only — no human safety data. The low flag rests on rodent/cell studies; there is no isolated-molecule human toxicity or interaction dataset.
• Possible additive sedation. The parent extract’s GABAergic activity means theoretical additive effects with sedatives; immune (Th1) modulation is worth noting in autoimmune/immunosuppressed contexts.
• Pregnancy is an herb-level call. Ashwagandha is traditionally avoided in pregnancy; that precaution belongs to the herb/product, not to conclusions about this molecule.

Dosage

No human therapeutic dose exists and none is recommended. For context only, research exposures are: in vitro, low-micromolar (~1 µM) for the neurite-outgrowth/neuroregeneration effects ^{1,2,3Reference 1Kuboyama T et al. · 2005Neuritic regeneration and synaptic reconstruction induced by withanolide AView study →Reference 2Kuboyama T et al. · 2002Axon- or dendrite-predominant outgrowth induced by constituents from AshwagandhaView study →Reference 3Zhao J et al. · 2002Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activitiesView study →}; in vivo, oral rodent dosing of Withania preparations and related withanosides in the memory/neurodegeneration models ^{6Reference 6Kuboyama T et al. · 2006Withanoside IV and its active metabolite, sominone, attenuate Aβ(25-35)-induced neurodegenerationView study →}, with the molecule showing rapid but modest oral absorption in mice ^{11Reference 11Patil D et al. · 2013AnimalDetermination of withaferin A and withanolide A in mice plasma using HPLC-tandem mass spectrometry: application to pharmacokinetics after oral administration of Withania somnifera aqueous extractView study →}. Human intake of withanolide A is indirect — as one minor withanolide within standardized root extracts dosed for stress/anxiety/sleep (commonly 300–600 mg/day of extract in trials) ^{12Reference 12Chandrasekhar K et al. · 2012RCTA prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adultsView study →}, not as an isolated compound. These are doses studied in research and are not a personal recommendation.

References

1. Kuboyama T, Tohda C, Komatsu K (2005). Neuritic regeneration and synaptic reconstruction induced by withanolide A. British Journal of Pharmacology. https://pubmed.ncbi.nlm.nih.gov/15711595/
2. Kuboyama T, Tohda C, Zhao J, Nakamura N, Hattori M, Komatsu K (2002). Axon- or dendrite-predominant outgrowth induced by constituents from Ashwagandha. Neuroreport. https://pubmed.ncbi.nlm.nih.gov/12395110/
3. Zhao J, Nakamura N, Hattori M, Kuboyama T, Tohda C, Komatsu K (2002). Withanolide derivatives from the roots of Withania somnifera and their neurite outgrowth activities. Chemical & Pharmaceutical Bulletin. https://pubmed.ncbi.nlm.nih.gov/12045329/
4. Tohda C, Kuboyama T, Komatsu K (2005). Search for natural products related to regeneration of the neuronal network. Neurosignals. https://pubmed.ncbi.nlm.nih.gov/15956813/
5. Crane EA, Heydenreuter W, Beck KR, Strajhar P, Vomacka J, Smiesko M, Mons E, Barth L, Neuburger M, Vedani A, Odermatt A, Sieber SA, Gademann K (2019). Profiling withanolide A for therapeutic targets in neurodegenerative diseases. Bioorganic & Medicinal Chemistry. https://pubmed.ncbi.nlm.nih.gov/30929949/
6. Kuboyama T, Tohda C, Komatsu K (2006). Withanoside IV and its active metabolite, sominone, attenuate Aβ(25-35)-induced neurodegeneration. European Journal of Neuroscience. https://pubmed.ncbi.nlm.nih.gov/16553605/
7. Dar NJ, Gull B, Hamid A, Ahmed Z, Ahmad M (2025). Withaferin-A kills neuronal cells: an off-putting facet of Withania somnifera as a neuroprotectant. Steroids. https://pubmed.ncbi.nlm.nih.gov/40695418/
8. Bhattacharya SK, Bhattacharya A, Sairam K, Ghosal S (2000). Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental study. Phytomedicine. https://pubmed.ncbi.nlm.nih.gov/11194174/
9. Candelario M, Cuellar E, Reyes-Ruiz JM, Darabedian N, Feimeng Z, Miledi R, Russo-Neustadt A, Limon A (2015). Direct evidence for GABAergic activity of Withania somnifera on mammalian ionotropic GABA-A and GABA-ρ receptors. Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/26068424/
10. Malik F, Singh J, Khajuria A, Suri KA, Satti NK, Singh S, Kaul MK, Kumar A, Bhatia A, Qazi GN (2007). A standardized root extract of Withania somnifera and its major constituent withanolide-A elicit humoral and cell-mediated immune responses by up regulation of Th1-dominant polarization in BALB/c mice. Life Sciences. https://pubmed.ncbi.nlm.nih.gov/17336338/
11. Patil D, Gautam M, Mishra S, Karupothula S, Gairola S, Jadhav S, Pawar S, Patwardhan B (2013). Determination of withaferin A and withanolide A in mice plasma using HPLC-tandem mass spectrometry: application to pharmacokinetics after oral administration of Withania somnifera aqueous extract. Journal of Pharmaceutical and Biomedical Analysis. https://pubmed.ncbi.nlm.nih.gov/23584079/
12. Chandrasekhar K, Kapoor J, Anishetty S (2012). A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian Journal of Psychological Medicine. https://pubmed.ncbi.nlm.nih.gov/23439798/

View all 12 references▾