Root Versus Leaf: Why the Plant Part in Your Ashwagandha Supplement Matters for Safety

Ashwagandha has become one of the best-selling herbal supplements in the world, marketed for stress, sleep, vitality, and cognitive resilience. Yet a comprehensive new review published in Food Science & Nutrition argues that the question most consumers, and even many regulators, have never asked may be the most important one of all: which part of the plant is actually in the bottle? The structured narrative review, which sifted more than 1,500 records down to 56 included studies spanning traditional texts, phytochemistry, preclinical pharmacology, human trials, and regulatory documents, concludes that ashwagandha root and leaf are not interchangeable ingredients, and that treating them as a single undifferentiated herb has distorted both safety assessment and regulation.

The distinction begins with chemistry. Ashwagandha’s bioactivity is dominated by steroidal lactones called withanolides, but the withanolide profile differs sharply between organs. Comparative HPLC and UHPLC–MS/MS analyses show that leaves accumulate high levels of withaferin A and related epoxide-bearing withanolides, compounds with potent cytotoxic and anti-inflammatory properties. Roots, by contrast, are relatively enriched in withanolide A, withanolide D, and glycowithanolides, the marker compounds used in pharmacopoeial monographs and standardized commercial root extracts. In chemotype studies such as the variety Poshita, withaferin A peaks in field-grown leaves while withanolide A predominates in roots across multiple chemotypes, establishing a consistent gradient between the more cytotoxic leaf chemistry and the so-called tonic-type root chemistry.

That gradient maps onto a long history of differentiated use. Classical Ayurvedic texts describe ashwagandha primarily as a root-based Rasayana, a rejuvenating tonic prescribed as a powder with milk or ghee for stress, debility, insomnia, and neuromuscular disorders. The leaf appears only sparsely in the classical compendia but features prominently in regional and tribal ethnomedicine across India, where it is applied as pastes, poultices, and decoctions for painful swellings, wounds, boils, scorpion stings, and dental pain, and occasionally ingested for fever and metabolic complaints. In other words, tradition itself drew a line between the root as a systemic tonic and the leaf as a more localized, indication-specific remedy, a historical differentiation of expected benefit–risk profiles that modern science is now rediscovering.

Preclinical pharmacology reflects both shared and distinct activities. Root extracts show robust anti-stress, anxiolytic, anti-inflammatory, cardioprotective, and neuroprotective effects in rodent models, mechanisms linked to modulation of the hypothalamic–pituitary–adrenal axis, GABAergic and serotonergic signaling, and the NF-κB and Nrf2 pathways. Leaf extracts, richer in withaferin A and other electrophilic withanolides, display striking anticancer, immunomodulatory, and neuroprotective activity in vitro and in selected animal models, including selective killing of tumor cells and inhibition of NF-κB and STAT3 signaling. In some comparative experiments leaf preparations match or exceed root extracts on antioxidant and antitumor endpoints, but these studies typically employ higher withaferin A exposures over short durations, leaving the translational safety margins for chronic oral use in humans undefined.

The human evidence base is even more lopsided. Nearly all controlled clinical data derive from root extracts, typically at doses of 240 to 600 milligrams per day, and randomized double-blind placebo-controlled trials in adults with stress, anxiety, or poor sleep consistently report improvements in perceived stress, anxiety scales, sleep quality, and cortisol, with favorable tolerability over 6 to 12 weeks. A 12-month open-label study of a standardized root extract at 600 milligrams per day found no serious adverse drug reactions and no signal for cumulative hepatic, renal, thyroid, or hematologic toxicity, and a systematic review covering 30 clinical trials of root preparations reported no serious adverse events across indications ranging from chronic stress to rheumatoid arthritis and male infertility.

Leaf-specific human data are minimal but revealing. A Phase I open-label trial of a pharmaceutical-grade leaf extract known as RH324 in patients with advanced non-small cell lung cancer reported tolerability and preliminary disease stabilization over 28 days, while a separate Phase I study of a leaf-derived preparation in osteosarcoma patients recorded dose-dependent liver enzyme elevations in five of eleven participants. A small number of randomized trials have tested combined root-and-leaf aqueous extracts for chronic stress and resistance training, but these remain limited. The review’s authors stress that this sparse record does not prove the leaf is inherently unsafe; rather, the leaf evidence is insufficient for chronic systemic use, a critical distinction that much of the current regulatory debate has blurred.

Complicating the picture further is adulteration. The US Botanical Adulterants Prevention Program has documented frequent detection of leaf material in commercial products labeled as root or root-only extract, driven by economics: leaves are cheaper, renewable, and richer in withaferin A. Crucially, the program warns that assays based solely on total withanolides cannot distinguish root from leaf, since withanolides occur throughout the plant. Reliable authentication requires orthogonal methods combining HPTLC or HPLC fingerprinting, targeted quantification of withaferin A and quercetin-related metabolites, and DNA-based tools. This matters because some of the toxicological signal in European risk evaluations derives from studies on leaf or whole-plant preparations rather than authenticated root.

The regulatory consequences have been dramatic. In 2020, a literature-based risk assessment by the Technical University of Denmark concluded that a safe intake level for ashwagandha in supplements could not be established, citing potential thyroid and sex hormone effects and possible abortifacient properties, prompting Denmark to ban ashwagandha-containing supplements from 2023. Independent critiques argue the assessment over-weighted limited animal and case-report data, relied on low-quality sources, and conflated root with leaf and whole-plant preparations while overlooking the broader clinical safety dataset on standardized root extracts. Subsequent evaluations by the Dutch RIVM, Germany’s BfR, France’s ANSES, and the UK Food Standards Agency have flagged hepatotoxicity, thyroid, and reproductive concerns, even while acknowledging that much of the adverse-event literature involves products of uncertain composition and plant part.

Pharmacovigilance adds another layer of ambiguity. Published case reports of liver injury in ashwagandha users describe products that were never analytically characterized for plant part, and causality assessments using the RUCAM method reached only possible or probable scores, never definite. One research group has hypothesized that undeclared leaf adulteration, with its substantially higher withanone and withaferin A content, could contribute to hepatotoxicity, providing a plausible mechanistic basis for the case clusters. If some European hepatotoxicity reports in fact reflect exposure to unlabeled leaf or whole-plant material sold as root, then the central regulatory problem is quality and authenticity rather than plant identity alone, and plant-part-agnostic risk assessments risk punishing the wrong ingredient.

The review’s prescriptions are concrete. Monographs and guidance should define ashwagandha for internal use as root or root extract unless leaf or aerial parts are explicitly declared, with separate dossiers and safety data required for leaf products. Regulators should mandate validated orthogonal authentication methods in manufacturing release and market surveillance, treat undeclared aerial-part content as adulteration, and consider a dose-based framework for leaf anchored to withaferin A limitation, analogous to thresholds set for pyrrolizidine alkaloids, once adequate human pharmacokinetic and dose-escalation data exist to derive a safe exposure level. Priority research needs include comparative randomized trials of authenticated root, leaf, and whole-plant extracts with matched chemotyping, comprehensive hepatic, thyroid, and reproductive safety studies for leaf preparations, and a plant-part-stratified meta-analysis of adverse events across all published trials. Until such data arrive, the authors conclude, authenticated root remains the best-characterized material for systemic use, and the case for treating ashwagandha as a plant-part-specific medicine, not a generic herb, is now firmly on the scientific and regulatory agenda.

Subject of Research: Comparative safety, efficacy, and regulation of ashwagandha root versus leaf preparations

Article Title: Plant Part–Specific Differences in Ashwagandha (Withania somnifera): A Comparative Evaluation of Root and Leaf Evidence for Safety and Regulation

Article References: Dutta, A., & Gupta, J. B. (2026). Plant Part–Specific Differences in Ashwagandha ( Withania somnifera ): A Comparative Evaluation of Root and Leaf Evidence for Safety and Regulation. Food Science & Nutrition, 14(10), Article e72364. https://doi.org/10.1002/fsn3.72364

Image Credits: AI Generated

DOI: 10.1002/fsn3.72364

Keywords: ashwagandha, Withania somnifera, withanolides, withaferin A, herbal supplements, hepatotoxicity, adulteration, phytochemistry, regulation, Ayurveda, food safety, clinical trials