IngredientsWithanolides are a group of steroidal lactones commonly found in the Solanaceae family. More precisely, withanolides belong to a group of naturally occurring C-28 steroid lactones that are generally highly oxygenated, and these functionalities have led to many structural modifications. Since the discovery of the archetype withaferin A in 1965, approximately 900 of these naturally occurring, polyoxygenated steroidal lactones with 28-carbon ergostane skeletons have been discovered across 24 diverse structural types. Withanolides are steroidal and bear a resemblance, both in their action and appearance, to the active constituents ginsenosides present in Asian ginseng (Panax ginseng).
The class takes its name from the genus Withania. The structurally most studied individual withanolides include withaferin A (the first isolated member), withanolide A, withanolide B, withanolide D, withanone, withanoside IV, and 12-deoxywithastramonolide, among many others. The chemical name of withanolide A, for example, is (20R)6α,7α-Epoxy-5α,20β-dihydroxy-1-oxowitha-2,24-dienolide, and it has been associated with immunomodulatory, inhibition of cholinesterase activity, and neuritic rejuvenation activity.
Withania somnifera, an evergreen shrub in the nightshade family (Solanaceae), is native to India, North Africa, and the Middle East and is used in traditional systems of medicine, particularly Ayurvedic medicine in India, where it is known as ashwagandha. Withania somnifera is an evergreen undershrub that can reach over 3 feet high (1 meter) by 1 foot 8 inches wide (0.5 meter) that grows in open places in a great variety of soils, preferably dry and stony, disturbed environments, fully exposed to the sun. Common English names for the plant include Indian ginseng and winter cherry.
Withanolides, isolated primarily from genera belonging to the plant family Solanaceae, have captured interest mainly due to their diverse structural features and significant biological activities against several diseases. While Withania somnifera is the primary commercial and research source, withanolides are also found in other Solanaceae genera including Physalis, Nicandra, and Athenaea species.
Laboratory analysis has revealed more than 35 chemical constituents contained in the roots of W. somnifera. The biologically active chemical constituents are alkaloids (isopellertierine, anferine), steroidal lactones (withanolides, withaferins), saponins containing an additional acyl group (sitoindoside VII and VIII), and withanolides with a glucose at carbon 27 (sitoindoside XI and X). The roots of W. somnifera consist primarily of withanolides, which are believed to account for its extraordinary medicinal properties.
Analysis has demonstrated that root-contained withanolide A is de novo synthesized within roots from primary isoprenogenic precursors; therefore, withanolides are synthesized in different parts of the plant through operation of the complete metabolic pathway, rather than imported.
Extracts of ashwagandha root are often supplied as capsules or tablets in concentrations of 150 to 600 mg, which are taken one to three times daily, the total daily dose varying widely. W. somnifera-based herbal formulations are marketed in the form of supplement, extract, capsule, powder, etc.
Commercially, extracts are standardized to guaranteed minimum withanolide content. Two prominently studied proprietary extracts are KSM-66 (a full-spectrum root extract) and Sensoril® (a combined root and leaf aqueous extract). Among the various ashwagandha extracts available on the market, the standardization of actives, analytical methodologies, plant parts used, manufacturing methods, and recommended dosages vary considerably. These variables can potentially impact absorption characteristics and related therapeutic efficacy.
Considering the plasma AUC of total withanolides per mg of each W. somnifera extract administered orally, an extract with 35% withanolide glycosides was 280.74 times more bioavailable than a 2.5% withanolide extract. The results of this study highlight the importance of withanolide glycosides in improving the pharmacokinetics of W. somnifera extracts. However, limited human data are available on the bioavailability and metabolism of withanolides overall.
Withanolides, and in particular extracts from Withania somnifera, have been used for over 3,000 years in traditional Ayurvedic and Unani Indian medical systems as well as within several other Asian countries. Ashwagandha is an herb that can be dated back to the Vedic age and later used in Ayurveda. In the Rigveda and Atharvaveda, ashwagandha is mentioned as "Asvabati." Ashwagandha is a crucial herb mentioned in Ayurveda in the Charaka Samhita, Susruta Samhita, and Astanga Hridaya.
In Ayurveda, Withania somnifera is categorized as a "Rasayana" having a potential to boost the body's resistance against various diseases, revive the body functions in enervated conditions, and slow down aging. Ashwagandha is considered a potent rasayana (rejuvenative tonic) in Ayurveda, known for its ability to promote longevity, strength, and intellectual capacity.
According to Ayurvedic scholar Charaka in 10 BCE, the herb is recommended to get sharp memory, obtain longevity, get freedom from disease, and get the strength of a horse. According to the Charaka Samhita and Sushruta Samhita, ashwagandha is recommended for those suffering from weakness, tiredness, poor body weight, and neurological problems.
Traditionally, the extracts were ascribed a wide range of pharmacological properties with corresponding medical uses, including adaptogenic, diuretic, anti-inflammatory, sedative/anxiolytic, cytotoxic, antitussive, and immunomodulatory.
In Withania somnifera (family Solanaceae), the roots, leaves, flowers, and seeds have all been used for a variety of ailments. Various parts of W. somnifera, including its leaves, berries, seeds, and especially roots, are used in traditional systems of medicine. Traditionally, topical application of the berries and leaves of this plant is used as a remedy for ulcers and tumors.
Traditional preparations in Ayurveda were diverse. Ashwagandha is usually made into churna (powder), avaleha (a paste or jam), kvatha (a decoction), or arishta (a fermented infusion). In the Unani system, ashwagandha is classified as a "nervine tonic" and is used to help restore the body's vital humors.
Ashwagandha is rich in phytochemicals, including steroidal lactones (known as withanolides) and alkaloids. While withanolides are believed to be responsible for many of ashwagandha's proposed effects, evidence from preclinical studies suggests that other, non-withanolide components may also be involved.
The most pharmacologically studied individual withanolides include:
Other secondary metabolites in W. somnifera include anthocyanins, saponins, carotenoids, glycosides, lignins, tannins, flavonoids, phytosterols, and withanamides (A–I).
Extensive pharmacological research has identified multiple mechanisms of action across key inflammatory pathways. Major withanolides play roles within essential and supportive inflammatory pathways including NF-κB, JAK/STAT, AP-1, PPARγ, Hsp90, Nrf2, and HIF-1.
A number of naturally occurring withanolides such as chantriolide A, physalins A, B, C, and O, viscosalactone B, WA, withanolides D, E, F, and withaferin A 4,27-diacetate have been reported to modulate the regulation of NF-κB. At the molecular level, WA was shown to inhibit TNFα-induced activation of IκB kinase β (IKKβ) via a thioalkylation-sensitive redox mechanism. IKKβ Ser-181 hyperphosphorylation induced by WA led to inhibition of IκBα phosphorylation and degradation, which prevented NF-κB translocation, NF-κB/DNA binding, and gene transcription.
It has been shown that withaferin A can stably bind to the glucocorticoid receptor (GR), promoting its translocation into the nucleus in different types of cultured cells. This results in an anti-inflammatory effect via a transrepression mechanism. Withaferin A may exert its anti-stress effects through its capacity to bind and modulate the glucocorticoid receptor.
Withanolides have been described as adaptogens that assist with balance and regulation of the body's physiologic response to stressors. The adaptogen mechanism of effect has been proposed to occur through modulation of the HPA axis, inducing stress-activated c-Jun N-terminal protein kinase (JNK1), inhibiting iNOS expression, and modulation of Hsp70 chaperone function.
WS may alleviate stress-related conditions predominantly through modulation of the hypothalamic-pituitary-adrenal and sympathetic-adrenal medullary axes, as well as through GABAergic and serotonergic pathways.
Withanolides such as WA and withalongolide A are known to block Hsp90 chaperone function through blocking the Hsp90/cdc37 complex and induction of thiol-mediated oxidative stress. The Hsp90/cdc37 complex facilitates the active conformation of client kinases in particular, such as Akt, cyclin-D1, raf-1, and cdk4. Blocking this complex leads to dysfunctional or proteasome-mediated degradation of these kinases within multiple oncogenic, pro-survival, and proliferative kinase cascades (p38/MAPK, PI3K/Akt/mTOR, NF-κB pathways), which ultimately leads to cancer cell apoptosis.
Withanolides regulate genes involved in cell proliferation, apoptosis, immune responses, and energy metabolism through effects on transcription factors such as NF-κB, AP-1, and p53.
This is the area with the strongest and most replicated human clinical evidence for withanolide-containing extracts. In randomized clinical trials, ashwagandha reduced serum and salivary cortisol levels by 14–28%, correlating with a reduction in symptoms of chronic stress.
A well-controlled dose-ranging trial specifically examined the Sensoril® extract: consumption of standardized Withania somnifera extract of leaves and roots (Sensoril®) at doses of 125 mg, 250 mg, and 500 mg for 8 weeks safely and effectively reduced stress parameters in chronically stressed subjects, including reductions in stress, anxiety, and depression. Primary outcomes included salivary alpha-amylase, plasma cortisol, adrenocorticotropin (ACTH), and sulfate adrenal androgen dehydroepiandrosterone (DHEA-S).
The withanolide-rich extracts tested in studied interventions may have indirectly reduced cortisol levels by reducing inflammation, since chronic inflammation disrupts glucocorticoid receptor sensitivity and amplifies the stress-reactive system.
Evidence strength: Multiple randomized placebo-controlled trials and systematic reviews support a meaningful effect on perceived stress and cortisol biomarkers. Research suggests that ashwagandha extracts may lower stress, anxiety, and cortisol levels. A taskforce created by the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments provisionally recommends specific daily doses of ashwagandha root extract for the treatment of generalized anxiety disorder, but they also note that they cannot provide a stronger recommendation without more data.
WS root and leaf extracts exhibited noteworthy anti-stress and anti-anxiety activity in animal and human studies. WS also improved symptoms of depression and insomnia, though fewer studies investigated these applications.
A 2024 systematic review and meta-analysis searched Medline, Cochrane Library, and Google Scholar until August 2023 for randomized controlled trials comparing W. somnifera to placebo in patients with anxiety and/or insomnia. Outcome measures included changes in anxiety levels via the Hamilton Anxiety Scale (HAM-A), Sleep Onset Latency (SOL), Total Sleep Time (TST), Wake After Sleep Onset (WASO), Total Time in Bed (TIB), Sleep Efficiency (SE), and Pittsburgh Sleep Quality Index (PSQI) score.
WS may alleviate these conditions predominantly through modulation of the hypothalamic-pituitary-adrenal and sympathetic-adrenal-medullary axes, as well as through GABAergic and serotonergic pathways. While some studies link specific withanolide components to its neuropsychiatric benefits, there is evidence for the presence of additional, as yet unidentified, active compounds in WS. Significant variability in the WS extracts examined prevents a consensus on the optimum WS preparation or dosage for treating neuropsychiatric conditions.
Despite the historical neurological use of Withania somnifera, limited evidence supports its efficacy for conditions like anxiety and insomnia. Most trials have been small, short in duration, and conducted with different extract preparations, limiting cross-study comparisons.
Evidence strength: Preliminary to moderate. Multiple RCTs show positive direction of effect, but heterogeneity of preparations and small sample sizes reduce the strength of conclusions. International guidelines have issued only provisional recommendations pending larger trials.
One 8-week prospective randomized, double-blind, placebo-controlled multicenter study enrolled 80 healthy male and female participants aged 18–45 who engaged in regular physical activity. This study investigated the effects of 600 mg standardized root extract (>5% withanolides) of ashwagandha on muscle size, strength, and cardiorespiratory endurance following resistance training. Participants were randomly allocated to receive ashwagandha 300 mg capsules twice daily for eight weeks or identical placebo.
A prior study by the same research group also demonstrated that as an adjunct to a resistance training program, 600 mg of ashwagandha supplementation for eight weeks increased muscle strength in untrained male adults. Although preliminary studies have been conducted, robust human clinical trials evaluating the performance-enhancing effects of standardized AG root extract are still limited. A previously published study evaluating muscle strength focused only on male participants, and data on muscle strength and endurance in female participants is scarce.
Evidence strength: Preliminary to moderate. Several small RCTs and a meta-analysis show positive trends for upper body strength and VO2max, but trials have been short, involved selected populations, and results have not been consistently replicated in well-powered trials across both sexes.
Evidence for beneficial influence of ashwagandha supplementation on male fertility is rather promising, with significant increases in sperm concentration, semen volume, sperm motility, testosterone, and luteinizing hormone levels reported.
The proposed mechanism involves the structural similarity between withanolides and steroid hormones, as well as cortisol reduction: increased levels of anabolic hormone (serum testosterone) may be the cause of improved muscular strength, which could be associated with the structural similarities to withanolides as major constituents of ashwagandha root extract.
Evidence strength: Preliminary. Human trials on male fertility show consistent positive signals for semen parameters and testosterone, but most trials are small, of short duration, and some lack full methodological rigor. Larger replicated trials are needed before firm conclusions can be drawn.
WS improves memory and cognitive function when treating neurodegenerative rodent models, and in healthy adults significantly improves psychomotor function as demonstrated by simple reaction times, choice discrimination, digit symbol substitution, digit vigilance, and card sorting tests compared to placebo.
The root extract of Withania somnifera is used as a popular herbal drug in Ayurvedic medicine and has been used traditionally as a tonic and nootropic agent. It has been shown to facilitate cognitive function and augment mental retention capacity following diabetes- and scopolamine-induced memory loss. It is also known to augment cholinergic activity in the hippocampus.
Current research on ashwagandha covers many aspects of human health, including neuroprotective, sedative, and adaptogenic effects, and effects on sleep.
Evidence strength: Preclinical evidence is substantial. Human clinical evidence is early-stage: there are several small RCTs showing improvements in memory, reaction time, and executive function in both healthy adults and cognitively impaired populations, but evidence remains insufficient to establish clinical recommendations.
By altering natural and acquired immunity, boosting natural killer cell activity, controlling T- and B-cell responses, and altering cytokine levels, ashwagandha is being researched for its potential to alter the immune system.
Several studies have examined the beneficial effect of inhibiting transcriptional activity of NF-κB in chronic inflammatory diseases including cancer.
Evidence strength: Strong mechanistic and preclinical evidence. Human clinical evidence for specific inflammatory diseases is limited, and most immunological outcomes have been studied as secondary endpoints in stress and wellness trials.
Several studies have shown that withanolides such as WA, withalongolides A and B, tubocapsenolide A, and some of their synthetically modified analogues are able to target multiple cancers such as colon, prostate, brain, breast, head and neck, skin, adrenal, and thyroid both in vitro and in vivo.
Ashwagandha active substances, especially withaferin A (WA), are the most promising anti-cancer compounds. W. somnifera exerts its effect on breast cancer cells by inducing programmed cell death, especially apoptosis, at the molecular level. Ashwagandha has been found to possess a potential for treating breast cancer, especially estrogen receptor/progesterone receptor (ER/PR)-positive and triple-negative breast cancer.
Withanolides are generally regarded as safe and have been used in human clinical trials for inflammatory and neurologic diseases, and have been evaluated for the treatment of fatigue for breast cancer patients undergoing chemotherapy. Additional in vivo research on withanolides is ongoing and has overall been quite promising to identify withanolides as an important cancer therapy; however, further supporting research is needed to initiate the human clinical trials required to obtain a better understanding of the clinical treatment effects of withanolides on cancer.
Evidence strength: Preliminary. The overwhelming majority of evidence is in vitro and in animal models. No withanolide compound has yet achieved regulatory approval as an anti-cancer agent, and human clinical oncology trials remain at an early stage.
Extracts of ashwagandha root are often supplied as capsules or tablets in concentrations of 150 to 600 mg, which are taken one to three times daily, the total daily dose varying widely.
Dosages reported across key clinical investigations:
Significant variability in the WS extracts examined prevents a consensus on the optimum WS preparation or dosage for treating neuropsychiatric conditions. Among the various ashwagandha extracts available on the market, the standardization of actives, analytical methodologies, plant parts used, manufacturing methods, and recommended dosages vary considerably.
Side effects are uncommon and have not been clearly defined. Large doses can cause gastrointestinal upset. More specifically, large doses can cause gastrointestinal upset, diarrhea, nausea, and vomiting, probably because of direct irritation to the intestinal mucosa.
In one clinical tolerability study, participants' physical, hematological, and biochemical characteristics were normal, and no significant alterations or irregularities were observed in safety metrics like liver, kidney, and thyroid functions.
Ashwagandha has not been implicated in causing serum enzyme elevations during therapy but recently has been implicated in cases of clinically apparent liver injury. The cause of hepatotoxicity from products containing ashwagandha is unclear. Among the many ingredients, the withanolides have been most suspect. The possibility of mislabeling or adulteration with hepatotoxic herbal products is always an issue in commercial multi-ingredient dietary supplements.
Most cases of ashwagandha-associated liver injury have been mild-to-moderate in severity and self-limited in course, but fatal cases due to acute liver failure or acute-on-chronic liver failure have been described.
A recent study investigated liver biopsy samples from eight patients taking ashwagandha products, noting cholestatic injury and hepatocellular necrosis with portal-based inflammation.
Ashwagandha-associated herb-induced liver injury (HILI) presents with cholestatic hepatitis and can lead to the syndrome of acute-on-chronic liver failure with high mortality in those with pre-existing liver disease.
Proposed explanations for hepatotoxicity include idiosyncratic immune-mediated reactions, the formation of reactive metabolites in sensitive individuals, or interactions with concomitant medications leading to altered hepatic metabolism. Importantly, these cases are extremely uncommon relative to the widespread use of ashwagandha, and no consistent pattern of hepatotoxicity has been established. Moreover, most reports describe reversible events that resolve upon discontinuation, suggesting a non-intrinsic, individual-specific susceptibility rather than a general toxic effect of withanolides.
A key safety observation from meta-analysis concerns the formulation type: many case studies reporting liver toxicity involved supplements containing both leaves and roots, complicating the identification of the toxicity source. Analysis indicated that ashwagandha root exhibits a superior safety profile compared to non-root parts, particularly concerning liver and reproductive toxicity. Studies have suggested that withanone may induce hepatic DNA damage under certain conditions, while case series from India reported liver injury associated with multi-ingredient or non-root formulations.
Gastrointestinal side effects, immune hypersensitivity, liver toxicity, and endocrine disruption have been reported, particularly with prolonged or excessive usage. Metabolic transformation via cytochrome P450 enzymes can form reactive intermediates, leading to oxidative stress and hepatotoxicity.
The endocrine-modulating activity of ashwagandha has been implicated in thyrotoxicosis and adrenal suppression. However, a 2025 computational safety meta-analysis found that reproductive toxicity analysis confirmed that ashwagandha's root posed no significant risk in terms of hormonal disruption, thyroid toxicity, or fetal toxicity.
It will be important to investigate potential herb-drug interactions involving WS if used alongside pharmaceutical interventions. WS generally appears safe for human use; however, it will be important to investigate potential herb-drug interactions involving WS if used alongside pharmaceutical interventions.
Based on its pharmacological profile across peer-reviewed literature, interactions with the following drug classes have been discussed in the scientific literature: immunosuppressants (due to immunomodulatory effects), thyroid hormone medications (due to documented thyroid-stimulating effects in some studies), sedatives and CNS depressants (additive sedative potential via GABAergic mechanisms), and agents affecting blood glucose (due to the insulin-sensitizing effects observed in some trials).
Potential side effects of ashwagandha include liver injury and sedation. It may also be harmful for men with hormone-sensitive prostate cancer, because of potential effects on levels of sex hormones.
Recent studies have evoked concerns over the toxicity of the bioactive compounds, including withanolides, alkaloids, and sitoindosides. The U.S. Pharmacopeia (USP) has initiated an in-depth literature review in response to accumulating case reports of liver injury. A review emphasized the need for standardization and monitoring of ashwagandha products to mitigate such risks.
Data on safety in pregnancy remain insufficient in the scientific literature to establish a safety profile, and use during pregnancy is generally not supported by clinical evidence.
Health conditions that Withanolides may help support.
Withanolides, the principal bioactive steroidal lactones from Ashwagandha (Withania somnifera), are identified in published experimental reviews as phytoconstituents with anti-ALS activity. They exhibit neuroprotective, anti-inflammatory, and antioxidant effects relevant to ALS motor neuron pathology. Evidence is preclinical from cell and animal model studies.
Withanolides are the primary bioactive steroidal lactones of ashwagandha (Withania somnifera) responsible for its anxiolytic and adaptogenic effects. Clinical trials of ashwagandha extract standardized to withanolide content demonstrate significant reductions in anxiety, stress, and cortisol. They modulate GABA-A receptors, inhibit cortisol secretion, and regulate HPA axis activity.
Withanolides are the primary steroidal lactone bioactives in Ashwagandha (Withania somnifera) responsible for its adaptogenic, anxiolytic, and anti-stress effects. They modulate the HPA axis, reduce serum cortisol, and exhibit GABAergic activity. Multiple meta-analyses of withanolide-standardized extracts show statistically significant anxiety and stress reductions. Clinical products are standardized to 1.5–5% withanolides, most commonly at 300–600 mg/day.
Withanolides are the primary bioactive steroidal lactones of Ashwagandha responsible for its HPA axis-modulating, GABAergic, and emotional resilience-enhancing effects. Multiple RCTs use withanolide content as the standardization benchmark, with consistent reductions in cortisol, anxiety, and perceived stress scores vs. placebo.
The principal steroidal lactone bioactives of Ashwagandha (Withania somnifera), withanolides are the compounds most directly responsible for HPA axis modulation and cortisol attenuation documented in clinical trials. RCTs standardized to withanolide content (≥5%) confirm significant reductions in cortisol, ACTH, and perceived stress. They also influence GABAergic neurotransmission, contributing to anxiolytic effects.
Withanolides are the principal bioactive steroidal lactones of Withania somnifera (ashwagandha) responsible for its thyroid-supporting effects. They are proposed to directly stimulate thyroid hormone synthesis and enhance T4-to-T3 conversion, as evidenced by standardized withanolide-containing extracts showing normalized TSH, T3, and T4 in subclinical hypothyroid RCTs.
Withanolides are the primary bioactive steroidal lactones of Ashwagandha (Withania somnifera) associated with its adaptogenic and sleep-promoting properties. RCTs using extracts standardized to withanolides show significant improvements in insomnia severity, sleep efficiency, and sleep latency.
Withanolides are the principal bioactive steroidal lactones from Ashwagandha (Withania somnifera) responsible for its testosterone-supporting and adaptogenic effects in men. They reduce cortisol, have anabolic steroid-like activity, and multiple RCTs on standardized Ashwagandha extract defined by withanolide content have confirmed improvements in testosterone and male sexual function.
Withanolides are the steroidal lactone constituents of Ashwagandha (Withania somnifera) responsible for its adaptogenic, cognitive, and anti-fatigue effects. RCTs using withanolide-standardized extracts confirm improvements in memory, attention, vigilance, and mental alertness.
Withanolides are the primary neuroprotective steroidal lactones from Ashwagandha (Withania somnifera). Preclinical and clinical studies document their effects on Alzheimer's disease pathology, neural regeneration, GABA-A receptor modulation, and anti-neuroinflammation.
Withanolides (Withaferin A, Withanolide D) from Ashwagandha upregulate BDNF and NGF, normalize HPA axis cortisol suppression of hippocampal plasticity, and promote axonal/dendritic growth in hippocampal neurons. They are the specific bioactive compounds through which Ashwagandha's well-documented neuroplasticity effects are mediated.
Withanolides are the primary bioactive steroidal lactones in Ashwagandha (Withania somnifera) responsible for its adaptogenic effects on physical endurance. Standardized withanolide extracts have been shown in multiple RCTs to improve VO2max, cardiorespiratory endurance, and reduce fatigue. They modulate stress hormones, support anabolic signaling, and reduce exercise-induced oxidative stress.
The principal bioactive steroidal lactones in Ashwagandha (Withania somnifera), directly responsible for its adaptogenic and anti-stress effects. They modulate HPA axis function, inhibit NF-κB, and interact with glucocorticoid receptors to reduce cortisol in stressed subjects, as demonstrated in multiple RCTs.
Withanolides are the primary bioactive steroidal lactones in Ashwagandha (Withania somnifera) responsible for its testosterone-supporting effects. RCTs using ashwagandha extracts standardized to >5% or 35% withanolide content show significant testosterone increases of 14–17% in men. Withanolides are believed to act via cortisol reduction and HPG-axis disinhibition.
Withanolides are the primary steroidal lactone bioactives from Withania somnifera (ashwagandha) responsible for immunomodulatory and antiviral effects. They inhibit NF-κB, activate NK cells, and have demonstrated in vitro antiviral activity against influenza, infectious bronchitis coronavirus, and HIV-1.
Body systems that Withanolides may help support.
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