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KSM-66 Ashwagandha and Safety: What Every Adult Needs to Know Before Taking It

By the Daily Nutra Research Team  |  Updated July 2026

Ashwagandha has become one of the most widely used adaptogens on the market, praised for lowering cortisol, easing anxiety, and improving sleep. But "natural" doesn't automatically mean "risk-free" for everyone -- and a growing body of clinical literature is now mapping out exactly who should be cautious, at what doses, and why the extract you choose matters as much as whether you take it at all.

Checking the label matters: extract type, standardization, and dose all change ashwagandha's safety profile.

Ashwagandha (Withania somnifera) has one of the largest human safety databases of any adaptogenic herb, with dozens of randomized controlled trials reporting good overall tolerability at studied doses (1). That track record is real -- but it isn't the whole story.

Because ashwagandha influences the hypothalamic-pituitary-adrenal (HPA) axis, thyroid hormone signaling, and immune activity, it can meaningfully interact with several common conditions and medications. Case reports of liver injury, case series in people with autoimmune thyroid disease, and documented interactions with sedatives and immunosuppressants have all appeared in peer-reviewed literature in the past several years (2).

None of this means ashwagandha is dangerous for the average healthy adult -- clinical trials using standardized KSM-66 extract at 300-600mg/day have consistently shown adverse event rates similar to placebo (3). What it means is that "who takes it, which extract, and how much" are the three variables that actually determine risk.

The form of the extract matters enormously here. Generic, unstandardized ashwagandha powders vary wildly in withanolide content and can contain higher levels of naturally occurring alkaloids, while root-only extracts like KSM-66 are manufactured specifically to exclude the leaf material associated with a higher concentration of unwanted compounds.

This article walks through exactly what the safety research shows -- the documented side effects, who should talk to a doctor first, the medications that can interact with it, and how to choose a product that matches the dosing used in published human trials.

What Is Ashwagandha, and Why Does Extract Type Matter for Safety?

Withania somnifera, commonly called ashwagandha or "Indian ginseng," is a small shrub used in Ayurvedic medicine for centuries as a rasayana -- a rejuvenating tonic intended for long-term, low-dose use rather than short-term high-dose crisis intervention. That distinction matters more than most modern supplement labels let on.

The primary bioactive compounds are withanolides, steroidal lactones concentrated mainly in the root. Withanolides are what modulate cortisol and GABA-related signaling in the nervous system, but they are also the compounds responsible for ashwagandha's mild immune-stimulating and thyroid-active effects -- the same properties that create precautions for specific populations.

KSM-66® is a full-spectrum root-only extract standardized to ≥5% withanolides using a proprietary water-milk extraction process with no chemical solvents. Because it excludes leaf material and alkaloids concentrated outside the root, it has been the subject of more than 24 published human clinical trials -- giving it one of the most thoroughly documented safety profiles of any ashwagandha extract on the market.

How Ashwagandha Affects the Body: Why Certain Groups Need to Be Careful

Ashwagandha's core mechanism runs through the hypothalamic-pituitary-adrenal (HPA) axis -- the same stress-signaling loop that regulates cortisol release. Withanolides appear to blunt excessive cortisol output and support GABA-ergic calming pathways, which is the basis for its anti-stress and sleep benefits.

But the hypothalamus and pituitary gland don't just talk to the adrenal glands -- they also regulate the thyroid through thyroid-stimulating hormone (TSH). Multiple clinical trials have found that ashwagandha modestly raises T3 and T4 levels, which is genuinely helpful for people with subclinical hypothyroidism, but can push people with hyperthyroidism or Graves' disease into symptomatic territory (4).

Separately, ashwagandha has documented immunostimulant activity -- it can increase certain white blood cell activity and inflammatory signaling markers. For most people this is a feature, not a risk. But for anyone with an autoimmune condition (Hashimoto's, rheumatoid arthritis, lupus, MS) or anyone on immunosuppressant therapy after a transplant, stimulating immune activity can work directly against their treatment plan.

Finally, because withanolides act on GABA and sedation pathways, combining ashwagandha with benzodiazepines, sedatives, or thyroid medication without medical supervision can compound effects or shift dosing needs -- which is why several safety reviews specifically flag drug-interaction screening as a required step before starting supplementation (5).

None of these mechanisms make ashwagandha inherently harmful -- they simply explain why the same compound that helps one person's cortisol and sleep can complicate another person's thyroid panel or medication regimen.

Ashwagandha's HPA-axis mechanism touches the thyroid, GI tract, liver, and immune system -- which is why certain groups need extra caution.

What the Clinical Research Shows About Ashwagandha Safety

Liver Health: Rare But Documented Case Reports

A 2020 case series published in Liver International examined a small number of drug-induced liver injury cases linked to ashwagandha supplements, with symptoms including jaundice and elevated liver enzymes that resolved after discontinuation (2). The cases involved unstandardized or unidentified extracts in most instances, and liver injury has not been reported in the KSM-66-specific clinical trial literature, which includes repeated liver panel monitoring across multiple 60-90 day human studies showing no significant changes in liver enzymes versus placebo.

Thyroid Function: Helpful for Some, Risky for Others

A randomized, double-blind, placebo-controlled trial in subclinical hypothyroid patients found that ashwagandha root extract significantly normalized TSH, T3, and T4 levels over 8 weeks compared to placebo (4). That same thyroid-modulating effect is precisely why endocrinologists advise caution for people with hyperthyroidism, Graves' disease, or anyone on thyroid hormone replacement therapy -- the dose may need adjustment under medical supervision.

Pregnancy and Breastfeeding

Traditional Ayurvedic texts and modern safety reviews both flag ashwagandha as contraindicated during pregnancy, with animal research suggesting a potential to affect uterine activity at high doses (1). Human trial data during pregnancy and lactation is essentially absent, so the standard clinical recommendation is to avoid use entirely in this population until better-controlled data exists.

General Tolerability in Healthy Adults

Across the core KSM-66 clinical trial base -- including a landmark double-blind, placebo-controlled study in 60 chronically stressed adults over 60 days -- reported adverse events were mild, infrequent, and statistically comparable to placebo, most commonly limited to occasional GI discomfort or drowsiness (6). A separate safety-focused study in 80 healthy volunteers taking 600mg/day for 8 weeks found no clinically significant changes in blood counts, liver enzymes, kidney markers, or vital signs (3).

Autoimmune Conditions and Immune-Modulating Effects

Ashwagandha's immunostimulant properties -- generally a benefit for general wellness -- are specifically called out in clinical safety reviews as a reason for caution in people with autoimmune diagnoses such as Hashimoto's thyroiditis, rheumatoid arthritis, lupus, or multiple sclerosis, and in anyone taking immunosuppressive medication following organ transplant (5). These groups are consistently advised to consult their treating physician before starting supplementation.

Dosage, Form, and What to Look For on the Label

Across the human clinical trial literature, the effective and studied dose range for ashwagandha root extract is 300-600mg per day, typically taken once daily with food or split into two doses. Most trials ran for 8-12 weeks, with participants reporting meaningful improvements in stress and sleep measures beginning around week 2-4 and continuing to improve through the study period.

What to look for on the label:

• Ingredient specifically listed as KSM-66® or Withania somnifera root extract (KSM-66)
• Standardized to ≥5% withanolides
• Root extract only -- not leaf, stem, or "whole-plant" blends
• 600mg or less per serving, matching clinical trial dosing
• Third-party tested for heavy metals and contaminants

Avoid products that simply list "ashwagandha powder" or "ashwagandha root" without specifying a standardized, root-only extract -- these products can vary batch to batch in withanolide content and may carry a different risk profile than the extract used in published safety trials.

Safety Profile and Side Effects

At studied clinical doses, standardized KSM-66 ashwagandha is generally well-tolerated, with adverse event rates in controlled trials statistically similar to placebo. That said, mild side effects have been reported in a minority of participants, and understanding them helps you use the supplement responsibly rather than avoid it unnecessarily.

Mild side effects reported in a minority of participants include:

• Mild GI upset, nausea, or stomach discomfort, especially on an empty stomach
• Drowsiness or mild sedation, particularly at higher doses or with evening dosing
• Headache in a small percentage of users during the first 1-2 weeks
• Rare reports of diarrhea or loose stools at doses above 600mg/day
• Very rare case reports of liver enzyme elevation, primarily linked to unstandardized products

Take ashwagandha with food or a small snack to minimize GI sensitivity, start at the lower end of the dosing range during the first two weeks, and avoid combining with alcohol or other sedatives without first checking with a healthcare provider.

Who Should -- and Shouldn't -- Take Ashwagandha

Ideal Candidates

• Healthy adults dealing with everyday stress, occasional anxiety, or sleep disruption
• Adults with subclinical (mild, undertreated) hypothyroidism, ideally under physician monitoring
• Athletes and active adults looking for cortisol support and recovery benefits

Who Should Consult a Physician First

• Pregnant or breastfeeding individuals: insufficient human safety data; traditional and animal research flag potential uterine effects
• People with hyperthyroidism or Graves' disease: ashwagandha can raise thyroid hormone levels and worsen symptoms
• People with autoimmune conditions (Hashimoto's, lupus, RA, MS): immune-stimulating effects may counteract treatment goals
• Anyone on sedatives, benzodiazepines, thyroid medication, or immunosuppressants: potential for interaction or need for dose adjustment
• People with a history of liver disease: rare case reports of hepatotoxicity warrant extra caution and liver panel monitoring
• Anyone scheduled for surgery: ashwagandha may affect blood sugar and central nervous system activity, and is generally advised to be stopped 2 weeks prior

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References

1. Tandon N, Yadav SS. (2020). Safety and clinical adverse effects of Ashwagandha (Withania somnifera (L.) Dunal) - An overview. Journal of Ethnopharmacology. PubMed
2. Bjornsson HK, Bjornsson ES, Avula B, et al. (2020). Ashwagandha-Induced Liver Injury: A Case Series from Iceland and the US Drug-Induced Liver Injury Network. Liver International. PubMed
3. Salve J, Pate S, Debnath K, Langade D. (2019). Adaptogenic and Anxiolytic Effects of Ashwagandha Root Extract in Healthy Adults: A Double-blind, Randomized, Placebo-controlled Clinical Study. Cureus. PubMed
4. Sharma AK, Basu I, Singh S. (2018). Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. Journal of Alternative and Complementary Medicine. PubMed
5. Tandon N, Yadav SS. (2020). Safety and clinical adverse effects of Ashwagandha (Withania somnifera (L.) Dunal) - An overview. Journal of Ethnopharmacology. PubMed
6. 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. PubMed