Withaferin A

Withaferin A at a Glance

Withaferin A is the most-studied withanolide — a steroidal lactone — of ashwagandha, and it is chemically a reactive electrophile, meaning it forms covalent bonds with cysteine residues on proteins.

That reactivity explains its enormous preclinical anticancer literature and the breadth of targets attributed to it — proteasome, HSP90, vimentin, NF-kB, angiogenesis. A promiscuous covalent binder hits many things.

It is worth separating from ashwagandha’s adaptogenic reputation, which rests on the root’s withanolide mixture at ordinary doses rather than on this compound’s cytotoxic pharmacology.

What It's Used For

Withaferin A is the best-known steroidal lactone (withanolide) of ashwagandha and one of the most-studied natural anticancer molecules. Before any claim, the defining caveat: withaferin A is present at only trace-to-low levels in oral ashwagandha root, the form used in virtually all human trials (KSM-66, Sensoril/Shoden). So ashwagandha’s clinical adaptogen, stress, sleep and testosterone benefits are not attributable to withaferin A — the herb’s tolerability and the molecule’s pharmacology are separate stories. The calmer, non-electrophilic side of ashwagandha chemistry sits with the sibling withanolides — the neurotrophic withanolide A and the anti-stress sitoindoside glycowithanolide fraction. The molecule itself is a reactive electrophile: its α,β-unsaturated steroidal lactone acts as a Michael acceptor that covalently modifies reactive cysteines on many proteins, which is why it hits a broad target list (proteasome, HSP90, vimentin, NF-κB) ^{1,2,3,4Reference 1Yang H et al. · 2007The tumour proteasome is a primary target for the natural anticancer compound withaferin A isolated from Indian winter cherryView study →Reference 2Yu Y et al. · 2010Withaferin A targets heat-shock protein 90 in pancreatic cancer cellsView study →Reference 3Bargagna-Mohan P et al. · 2007The tumour inhibitor and antiangiogenic agent withaferin A targets the intermediate-filament protein vimentinView study →Reference 4Ichikawa H et al. · 2006Withanolides potentiate apoptosis, inhibit invasion and abolish osteoclastogenesis through suppression of NF-κB activation and NF-κB-regulated gene expressionView study →} and why it is cytotoxic rather than drug-like. Its entire efficacy literature is preclinical.

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 is preclinical, so scores reflect mechanistic depth, not clinical proof, and stay low by design. Each application links to its write-up.

01AnticancerPromising50%Broad in-vitro + mouse-xenograft mechanism across tumor types ^{1,2,3,4,5,6Reference 1Yang H et al. · 2007The tumour proteasome is a primary target for the natural anticancer compound withaferin A isolated from Indian winter cherryView study →Reference 2Yu Y et al. · 2010Withaferin A targets heat-shock protein 90 in pancreatic cancer cellsView study →Reference 3Bargagna-Mohan P et al. · 2007The tumour inhibitor and antiangiogenic agent withaferin A targets the intermediate-filament protein vimentinView study →Reference 4Ichikawa H et al. · 2006Withanolides potentiate apoptosis, inhibit invasion and abolish osteoclastogenesis through suppression of NF-κB activation and NF-κB-regulated gene expressionView study →Reference 5Mohan R et al. · 2004Withaferin A is a potent inhibitor of angiogenesisView study →Reference 6McKenna MK et al. · 2015Anti-cancer activity of withaferin A in B-cell lymphomaView study →}

02Anti-inflammatory / inflammasomeShaky34%Cell + mouse NLRP3/NF-κB models ^{8,9Reference 8Kim J et al. · 2015Withaferin A inhibits Helicobacter pylori-induced production of IL-1β in dendritic cells by regulating NF-κB and NLRP3 inflammasome activationView study →Reference 9Xia Y et al. · 2021Withaferin A alleviates fulminant hepatitis by targeting macrophage and NLRP3View study →}

03Metabolic (leptin sensitizer)Shaky28%One high-profile mouse study ^{10Reference 10Lee J et al. · 2016AnimalWithaferin A is a leptin sensitiser with strong antidiabetic properties in miceView study →}

04ImmunomodulatoryShaky16%Cytotoxicity-linked cell-death signals (root extract) ^{11Reference 11Turrini E et al. · 2016Withania somnifera induces cytotoxic and cytostatic effects on human T-leukemia cellsView study →}

Mechanisms

Unifying mechanism: withaferin A is a reactive electrophile whose unsaturated lactone acts as a Michael acceptor covalently modifying reactive cysteines — the promiscuity that explains both its broad target list and its cytotoxicity.

Pharmacokinetics

Load-bearing. Withaferin A is a reactive electrophile / covalent binder — its Michael-acceptor chemistry forms covalent adducts with protein cysteine thiols (vimentin Cys328, the proteasome, and others) ^{3,1Reference 3Bargagna-Mohan P et al. · 2007The tumour inhibitor and antiangiogenic agent withaferin A targets the intermediate-filament protein vimentinView study →Reference 1Yang H et al. · 2007The tumour proteasome is a primary target for the natural anticancer compound withaferin A isolated from Indian winter cherryView study →}, which is why it hits many targets and why it is cytotoxic rather than drug-like. Its pharmacokinetics are characterized only in animal models, with poor drug-likeness (high reactivity, low selectivity) and no validated human PK. And oral exposure from ashwagandha root is low — withaferin A is trace-to-low in whole-root products (leaf is richer), so the root-based standardized extracts used in human trials deliver minimal withaferin A, and systemic exposure to the molecule from typical supplementation is small.

Clinical trials

There is no published human efficacy trial of purified withaferin A for any indication. Human ashwagandha trials test root extracts low in withaferin A and cannot serve as evidence for the molecule — their stress, sleep, anxiety and testosterone results should not be attributed to withaferin A. The entire efficacy literature for withaferin A is preclinical.

Last checked: July 2026.

Toxicity & Safety

This page concerns isolated withaferin A, not whole ashwagandha root — and the two are very different. The molecule is intrinsically cytotoxic: it is investigated precisely because it kills cells (apoptosis, cell-cycle arrest, ROS generation, mitochondrial disruption), and its Michael-acceptor reactivity means non-selective covalent protein binding, i.e. off-target liability at higher exposure. It is not sold as a standalone supplement, and whole-root ashwagandha’s good tolerability does not transfer to the purified molecule. Its cytotoxic, antiproliferative and antiangiogenic activity also raises a plausible reproductive-toxicity concern. Interactions are theoretical, from mechanism rather than clinical data: additive effects with proteasome or HSP90 inhibitors or other cytotoxic chemotherapeutics, modulation of NF-κB/immune signaling alongside immunosuppressants, and possible additive glucose/leptin effects with antidiabetic agents ^{10Reference 10Lee J et al. · 2016AnimalWithaferin A is a leptin sensitiser with strong antidiabetic properties in miceView study →}. The moderate flag reflects an honest middle: the reactive cytotoxicity argues toward “high,” but real-world human exposure occurs almost entirely via low-withaferin-A root extracts, and there is no isolated-molecule human toxicity dataset to anchor a higher call.

Dosage

No human therapeutic dose exists and none is recommended. For context only, research doses are: in vitro, typically low-micromolar (~0.5–10 µM) for anticancer/anti-inflammatory effects; in mice, ~1.25–5 mg/kg/day intraperitoneally in the metabolic study ^{10Reference 10Lee J et al. · 2016AnimalWithaferin A is a leptin sensitiser with strong antidiabetic properties in miceView study →}, with oncology xenograft studies commonly ~2–8 mg/kg intraperitoneally. These are experimental parenteral animal doses in cytotoxicity research and are emphatically not a supplement or human-use recommendation.

References

1. Yang H, Shi G, Dou QP (2007). The tumour proteasome is a primary target for the natural anticancer compound withaferin A isolated from Indian winter cherry. Molecular Pharmacology. https://pubmed.ncbi.nlm.nih.gov/17093135/
2. Yu Y, et al. (2010). Withaferin A targets heat-shock protein 90 in pancreatic cancer cells. Biochemical Pharmacology. https://pubmed.ncbi.nlm.nih.gov/19769945/
3. Bargagna-Mohan P, et al. (2007). The tumour inhibitor and antiangiogenic agent withaferin A targets the intermediate-filament protein vimentin. Chemistry & Biology. https://pubmed.ncbi.nlm.nih.gov/17584610/
4. Ichikawa H, et al. (2006). Withanolides potentiate apoptosis, inhibit invasion and abolish osteoclastogenesis through suppression of NF-κB activation and NF-κB-regulated gene expression. Molecular Cancer Therapeutics. https://pubmed.ncbi.nlm.nih.gov/16818501/
5. Mohan R, et al. (2004). Withaferin A is a potent inhibitor of angiogenesis. Angiogenesis. https://pubmed.ncbi.nlm.nih.gov/15516832/
6. McKenna MK, et al. (2015). Anti-cancer activity of withaferin A in B-cell lymphoma. Cancer Biology & Therapy. https://pubmed.ncbi.nlm.nih.gov/26020511/
7. Vyas AR, Singh SV (2014). Molecular targets and mechanisms of cancer prevention and treatment by withaferin A, a naturally occurring steroidal lactone. The AAPS Journal. https://pubmed.ncbi.nlm.nih.gov/24046237/
8. Kim J, et al. (2015). Withaferin A inhibits Helicobacter pylori-induced production of IL-1β in dendritic cells by regulating NF-κB and NLRP3 inflammasome activation. Immune Network. https://pubmed.ncbi.nlm.nih.gov/26770181/
9. Xia Y, et al. (2021). Withaferin A alleviates fulminant hepatitis by targeting macrophage and NLRP3. Cell Death & Disease. https://pubmed.ncbi.nlm.nih.gov/33574236/
10. Lee J, et al. (2016). Withaferin A is a leptin sensitiser with strong antidiabetic properties in mice. Nature Medicine. https://pubmed.ncbi.nlm.nih.gov/27479085/
11. Turrini E, et al. (2016). Withania somnifera induces cytotoxic and cytostatic effects on human T-leukemia cells. Toxins (Basel) (root DMSO extract, not the isolate). https://pubmed.ncbi.nlm.nih.gov/27187469/

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