What Is KSM-66 Ashwagandha? The Most-Studied Form for Stress and Sleep

If you have looked at adaptogen supplements recently, you have almost certainly come across KSM-66. It appears on more product labels than any other ashwagandha extract, it has more published human clinical trials behind it than any other standardised form, and it tends to command a premium over generic ashwagandha products.

But what exactly is KSM-66? How does it differ from other ashwagandha extracts? What has the research actually investigated and what are the safety considerations that anyone buying an ashwagandha supplement should know about?

This post covers the science, the extract quality differences, and the regulatory picture honestly.

What Is Ashwagandha?

Ashwagandha botanical name Withania somnifera is a plant native to India, North Africa, and parts of the Mediterranean. It has been used in Ayurvedic medicine for over 3,000 years, where it is classified as a rasayana a rejuvenating herb associated with vitality, resilience, and longevity.

In modern supplement science, ashwagandha is classified as an adaptogen: a category of herbs and plants studied for their potential to modulate the body's response to physical and psychological stress primarily through effects on the hypothalamic-pituitary-adrenal (HPA) axis, which governs the body's cortisol stress response.

The plant's primary bioactive compounds are withanolides a family of steroidal lactones concentrated in the root. These are the compounds most consistently associated with ashwagandha's studied effects in clinical trials, and withanolide content is the key marker used to standardise ashwagandha extracts. Other bioactive compounds include sitoindosides, alkaloids, and flavonoids. Research suggests these compounds may modulate the HPA axis, influence GABAergic signalling (the brain's primary inhibitory system), and affect inflammatory pathways including NF-κB inhibition and Nrf2 activation.

What Makes KSM-66 Different?

KSM-66 is a patented, full-spectrum ashwagandha root extract produced by Ixoreal Biomed. Several features distinguish it from generic ashwagandha products:

Root-only extraction. KSM-66 uses only the root of the Withania somnifera plant no leaf material is included. This matters for both traditional alignment (Ayurvedic practice has historically used the root) and modern safety considerations, which are discussed below.

Standardisation to 5% withanolides. Each batch of KSM-66 is standardised to contain at least 5% withanolides by weight. This means that 300mg of KSM-66 contains a consistent, defined quantity of the primary bioactive compounds something that generic or non-standardised ashwagandha powder cannot guarantee. The withanolide content of generic ashwagandha products can vary significantly between batches.

Full-spectrum extract. The extraction process is designed to preserve the full range of naturally occurring compounds in the root, rather than isolating individual withanolides. The rationale is that the combined compounds may work together more effectively than any single isolated constituent.

Traditional milk-based extraction process. KSM-66 is extracted using a process inspired by traditional Ayurvedic preparation an initial soaking step in milk before solvent-free extraction. The manufacturer states this preserves compounds that might otherwise be lost in purely solvent-based extraction.

Clinical research volume. As of 2025, KSM-66 has over 24 published human clinical trials more than any other standardised ashwagandha extract. This makes it the most-studied form of ashwagandha in peer-reviewed literature, which is the primary reason it appears so frequently on quality supplement labels.

What Has the Research Investigated?

It is important to be precise about what follows: these are summaries of what clinical studies have investigated and found, not claims that KSM-66 supplements will produce these outcomes in any individual.

Ashwagandha has no EFSA-authorised health claims in the UK or EU. The claims associated with ashwagandha are on the EFSA "on-hold" list they have been neither approved nor rejected, and cannot currently be used on supplement labels or in product marketing.

Stress and Cortisol

The most consistently studied area for KSM-66 is psychological stress. A double-blind, randomised, placebo-controlled trial published in the Indian Journal of Psychological Medicine (Chandrasekhar et al., 2012) one of the foundational KSM-66 studies randomised 64 adults with a history of chronic stress to receive either 300mg of KSM-66 or placebo twice daily for 60 days. The KSM-66 group showed reductions across multiple validated stress scales (Perceived Stress Scale: 44% reduction; GHQ-28: 72.3% reduction; DASS: 71.6% reduction) and a 27.9% reduction in serum cortisol levels compared to placebo.

A 2025 systematic review and meta-analysis published in BJPsych Open (Bachour et al., 2025) — covering 15 randomised controlled trials with a combined sample of 873 participants — assessed the effects of ashwagandha supplementation on cortisol, stress, and anxiety in adults. The pooled analysis found significant reductions in stress and anxiety measures compared to placebo across the included trials.

A 2021 systematic review (Pratte et al.) identified seven studies investigating ashwagandha for stress and anxiety, including three using KSM-66 specifically, and found consistent results across extracts though the authors noted that most studies were conducted in India and that generalisability to other populations requires further investigation.

Sleep

An 8-week randomised, double-blind, placebo-controlled trial published in PLoS One (Langade et al., 2019) tested KSM-66 at 300mg twice daily in 80 healthy adults aged 18–50, half of whom had insomnia. In those with insomnia, the KSM-66 group showed improvements in sleep quality, sleep onset latency, total sleep time, and mental alertness on rising, as measured by validated rating scales and actigraphy. Those without insomnia also reported subjective improvements in sleep quality, though without the same scale of effect.

The NIH Office of Dietary Supplements (2024) referenced this trial in its professional fact sheet on ashwagandha as one of the better-quality studies in this area.

Physical Performance

KSM-66 has been investigated in the context of physical performance and recovery. A double-blind, placebo-controlled trial in healthy athletic adults found significant improvements in VO2max (cardiorespiratory endurance) over 8 and 12 weeks compared to placebo, alongside improvements in quality of life measures. Research has also examined KSM-66 in relation to muscle recovery and training adaptation, though this is a smaller evidence base than the stress and sleep literature.

What the Research Does Not Yet Establish

It is worth being clear about the limits of the evidence:

• Most trials have been conducted in Indian populations, which limits broader generalisability

• Sample sizes are typically modest (60–150 participants) and trial durations short (6–12 weeks)

• The mechanism by which withanolides produce their studied effects on cortisol and sleep is not fully established

• No EFSA health claim has been authorised, reflecting that the evidence base while growing has not yet met the regulatory bar for approved claims in the UK and EU

The Safety Picture: What You Should Know

This section is essential reading for anyone considering ashwagandha. The safety picture is more nuanced than most supplement marketing suggests, and it is directly relevant to why the form of ashwagandha you take matters.

Liver Safety and the European Regulatory Review

Over the past several years, a number of cases of liver injury associated with ashwagandha supplement use have been reported in the scientific literature. A 2023 review in Pharmaceuticals (Björnsson et al.) examined published case reports of ashwagandha-induced liver injury. Importantly, many of the implicated products contained both root and leaf material, or were not standardised for withanolide content.

Ashwagandha leaves contain higher concentrations of withanolides than the root, but also significantly higher concentrations of withaferin A a compound associated with hepatotoxicity (liver toxicity) at elevated doses in both preclinical and case-report data. Root-only, standardised extracts such as KSM-66 contain withanolides at controlled concentrations without the elevated withaferin A levels associated with leaf-containing products.

In 2023, Denmark restricted ashwagandha supplements on the basis of safety concerns, including potential liver toxicity, effects on thyroid hormone levels, and traditional use as an abortifacient. In June 2024, the EU Heads of Food Safety Agencies working group recommended prioritising ashwagandha for an Article 8 procedure under Regulation (EC) No. 1925/2006 a formal safety review process that could lead to restrictions on its use in food supplements across the EU.

As of the time of writing, the UK has not implemented restrictions on ashwagandha supplements. However, the regulatory picture in Europe is actively evolving, and it is a genuine reason to be attentive to product quality.

What the Root-Only Distinction Means in Practice

A comprehensive safety analysis using AI-assisted meta-analysis and QSAR toxicity modelling (Kolarek et al., 2025, PMC12682666) found that ashwagandha root exhibits a superior safety profile compared to non-root parts, particularly with regard to liver and reproductive toxicity and that when compared to a broad set of other herbal supplements, ashwagandha root had a better safety profile than most.

KSM-66's root-only extraction and standardisation to a defined withanolide content are therefore directly relevant to the safety concerns in the European regulatory review. The liver injury cases most frequently implicated non-standardised or leaf-containing products.

Who Should Exercise Caution

The following groups should consult a GP or healthcare professional before taking ashwagandha:

• Pregnant women ashwagandha has a documented traditional use as an abortifacient; it should be avoided in pregnancy

• People with thyroid conditions ashwagandha may influence thyroid hormone levels; those on thyroid medication should seek medical advice

• People with autoimmune conditions ashwagandha may have immunomodulatory effects

• People with liver conditions given the hepatotoxicity cases in the literature

• People taking sedatives or anxiolytics potential for additive CNS effects

• People taking immunosuppressants or thyroid medication potential for interactions

How KSM-66 Is Typically Taken

The doses most commonly used in published KSM-66 trials range from 300mg to 600mg per day, with some studies using twice-daily dosing (300mg morning and evening). Trial durations have typically been 6–12 weeks. A prospective 12-month observational study published in Phytotherapy Research (Salve et al., 2025) assessed the safety of standardised ashwagandha root extract over a full year in healthy adults and found it was well tolerated with no significant adverse events recorded providing reassurance on longer-term use at standard doses in healthy individuals without contraindications.

Nyra Nutrition's KSM-66 Ashwagandha uses the KSM-66 extract standardised to 5% withanolides from root only. If you are considering ashwagandha supplementation, read the label carefully and review the contraindications above. Consult your GP if you have any relevant health conditions or take regular medication.

KSM-66 vs Other Ashwagandha Extracts

Several standardised ashwagandha extracts are used in supplements. The most commonly encountered alongside KSM-66 are:

Sensoril a patented extract using both root and leaf, standardised to withanolide glycoside conjugates rather than withanolides. It has a meaningful clinical evidence base (several published trials) but uses leaf material, which is directly relevant to the safety discussion above.

Shoden a more recently developed extract standardised to a very high withanolide glycoside content (35%). Fewer published trials than KSM-66 as of 2025.

Generic ashwagandha powder/extract variable withanolide content, often not disclosed, may contain leaf material. This is the category most represented in the hepatotoxicity case reports.

KSM-66's distinction root-only, full-spectrum, standardised to 5% withanolides, with the largest clinical trial database of any ashwagandha extract makes it the most defensible choice for anyone prioritising both efficacy evidence and safety profile.

Frequently Asked Questions

Does KSM-66 ashwagandha have EFSA-authorised health claims?

No. Ashwagandha has no EFSA-authorised health claims in the UK or EU. The claims associated with ashwagandha are on the EFSA "on-hold" list pending further review and cannot currently be used on supplement labels or in product marketing. This post describes what research has investigated, not what a supplement is authorised to claim.

What makes KSM-66 different from regular ashwagandha?

KSM-66 is a patented, full-spectrum root-only extract standardised to at least 5% withanolides, with over 24 published human clinical trials. Generic ashwagandha products have variable withanolide content (often undisclosed), may contain leaf material, and typically have little or no clinical research specific to their extract.

Is ashwagandha safe?

The safety picture is nuanced. Root-only, standardised extracts like KSM-66 have a better documented safety profile than leaf-containing or non-standardised products. However, cases of liver injury have been reported in the literature most associated with non-standardised or leaf-containing products. Several European regulatory bodies are currently reviewing ashwagandha safety, and Denmark restricted it in 2023. Ashwagandha should be avoided in pregnancy and by those with thyroid or liver conditions. Always consult a healthcare professional if you have relevant health conditions.

What dose is used in KSM-66 clinical trials?

Published KSM-66 trials have most commonly used 300mg twice daily (600mg total per day) for 6–12 weeks. Some trials used 300mg once daily. A 12-month safety study found standardised root extract well tolerated at standard doses in healthy adults.

What is a withanolide?

Withanolides are a class of steroidal lactones the primary bioactive compounds in ashwagandha root. They are thought to be responsible for ashwagandha's studied effects in clinical trials, through mechanisms including modulation of the HPA axis (the cortisol stress response system) and GABAergic signalling. KSM-66 is standardised to contain at least 5% withanolides by weight.

Can I take KSM-66 with other supplements?

KSM-66 is sometimes combined with other adaptogens or relaxation-supporting nutrients. However, caution is warranted with sedatives, anxiolytics, thyroid medication, and immunosuppressants due to potential additive or interactive effects. Speak to a healthcare professional before combining ashwagandha with prescription medication.