Why be careful with ashwagandha? Safety, side effects, and who should avoid it
Ashwagandha has become one of the most widely used adaptogens in the world, and the clinical evidence behind KSM-66 is genuinely strong for stress, sleep, and cortisol regulation. But "well-studied" and "risk-free for everyone" are not the same thing. A small but real subset of people should be careful with ashwagandha, and knowing who they are — and why — is what separates a safe, evidence-based supplement choice from a preventable problem.
Reading the label matters: standardized extract, dose, and personal health history all affect how safely ashwagandha is used.
Ashwagandha (Withania somnifera) is generally regarded as safe in human clinical trials, with most studies reporting adverse event rates similar to placebo at doses of 300–600mg per day of standardized root extract (1). That safety record, however, comes from trials that screened participants carefully — excluding pregnant women, people with certain thyroid and autoimmune conditions, and those on specific medications.
Outside a controlled trial, none of that screening happens automatically. Ashwagandha affects the hypothalamic-pituitary-adrenal (HPA) axis, thyroid hormone output, and can influence blood sugar and blood pressure — which is exactly why it works for stress, but also exactly why certain people need to be cautious.
A 2021 case report and subsequent case series identified rare instances of drug-induced liver injury associated with ashwagandha supplementation, prompting researchers to call for more post-market surveillance and clearer product standardization (2).
This is where the specific extract matters. KSM-66® is a full-spectrum root-only extract standardized to ≥5% withanolides, manufactured with consistent, tested batches — the same form used in the majority of the human clinical trials referenced in ashwagandha safety literature. Generic, unstandardized ashwagandha powders carry more variability in potency and contaminant risk, which can make side effects less predictable.
This article breaks down exactly who should be careful with ashwagandha, what the documented side effects and interactions are, how dosing affects risk, and how to use it responsibly if you decide it's right for you.
What Is Ashwagandha (and KSM-66 Specifically)?
Withania somnifera, commonly known as ashwagandha or "Indian ginseng," is a root classified in Ayurvedic medicine as a rasayana — a rejuvenating herb traditionally used to build resilience to stress over thousands of years of recorded use.
Its primary bioactive compounds are withanolides, steroidal lactones believed to modulate the HPA axis and reduce cortisol reactivity, along with supporting thyroid hormone conversion and antioxidant activity in nervous tissue.
KSM-66® is a specific patented extract produced using a milk-based extraction process that preserves the root's natural withanolide ratio without using alcohol or chemical solvents. It's standardized to ≥5% withanolides, root-only (no leaf or stem), and is the most clinically studied ashwagandha extract on the market, appearing in more than 24 published human trials.
How Ashwagandha Works — and Why That Same Mechanism Creates Risk in Some People
Ashwagandha's core mechanism runs through the hypothalamus, pituitary gland, and adrenal glands — the HPA axis that governs the body's stress response. Chronic stress keeps this axis overactive, elevating cortisol and disrupting sleep, mood, and metabolic regulation.
Withanolides appear to blunt excessive cortisol output and improve the axis's ability to return to baseline after a stressor, which is the mechanism behind ashwagandha's benefits for stress and sleep (3).
But the same axis that governs cortisol also cross-talks with thyroid hormone regulation. Ashwagandha has been shown in small trials to increase T3 and T4 levels in people with subclinical hypothyroidism (4) — a benefit for some, but a real risk for people with hyperthyroidism or Graves' disease, where further increasing thyroid hormone could worsen symptoms.
Ashwagandha may also have mild blood-sugar-lowering and blood-pressure-lowering effects (5), which is generally beneficial for metabolic health but means people on diabetes or hypertension medication need to monitor for additive effects, particularly hypoglycemia.
Because ashwagandha is immunomodulating, some researchers caution it could theoretically stimulate immune activity in ways that are unhelpful for people with autoimmune conditions, though human evidence here remains limited (6).
Ashwagandha's HPA-axis mechanism explains both its benefits and the specific conditions where extra caution is warranted.
What the Clinical Research Shows About Ashwagandha Safety
Overall Tolerability in Healthy Adults
A systematic review of ashwagandha's safety and tolerability across multiple randomized controlled trials found that adverse event rates in the treatment groups were statistically similar to placebo, with the most common complaints being mild gastrointestinal upset, drowsiness, and headache (1). Trial durations ranged from 8 to 12 weeks at doses of 250–600mg/day.
Thyroid Function Changes
A 2018 randomized controlled trial in adults with subclinical hypothyroidism found that 600mg/day of ashwagandha root extract over 8 weeks significantly increased serum TSH normalization and T3/T4 levels compared to placebo (4). While beneficial for hypothyroid patients, this same effect is the basis for caution in people with hyperthyroidism, where excess thyroid hormone is already the problem.
Liver Safety Signals
Case reports published between 2020 and 2023 documented a small number of instances of cholestatic liver injury temporally associated with ashwagandha use, with liver function normalizing after discontinuation in all reported cases (2). These remain rare relative to the scale of global ashwagandha use, but they underscore why people with pre-existing liver conditions, and anyone on hepatotoxic medications, should talk to a doctor first.
Pregnancy and Reproductive Safety
Animal studies have shown ashwagandha can have abortifacient and uterine-stimulating effects at high doses (7), which is why it is not recommended during pregnancy. Human safety data in pregnant women is insufficient to establish a safe threshold, so the conservative clinical guidance is to avoid it entirely during pregnancy and while breastfeeding.
Blood Sugar and Blood Pressure Interactions
Small trials examining ashwagandha's metabolic effects found modest reductions in fasting blood glucose and blood pressure in some participants (5), which is why people on insulin, sulfonylureas, or antihypertensive medications should monitor for additive lowering effects, especially when 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 is 300–600mg per day of standardized root extract, typically taken once daily or split into two doses. Most trials ran 8–12 weeks, with participants reporting reduced perceived stress beginning around week 2–4.
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 or whole-plant)
- Minimum 300mg per serving, most studies use 600mg/day
- Third-party tested (NSF, Informed Sport, or equivalent)
Avoid products that simply list "ashwagandha powder" or "ashwagandha blend" without specifying a standardized, root-only extract — these products carry more variability in withanolide content and are harder to dose safely and predictably.
Safety Profile and Side Effects
KSM-66 has an established safety profile across dozens of human trials, with most adverse events reported as mild and comparable to placebo at doses of 300–600mg/day over periods up to 12 weeks. Serious adverse events are rare in the published literature but not absent, which is why screening for the risk categories below matters.
Mild side effects reported in a minority of participants include:
- Mild GI upset, especially on an empty stomach
- Drowsiness (generally beneficial with evening dosing)
- Headache in the first 1–2 weeks
- Rare cases of liver enzyme elevation (typically resolves after discontinuation)
Take with food to minimize GI sensitivity, start at the lower end of the dose range (300mg) for the first week, and discontinue if you notice unusual fatigue, jaundice, dark urine, or abdominal pain and consult a physician.
Who Should — and Shouldn't — Take Ashwagandha
Ideal Candidates
- Healthy adults managing everyday chronic stress or occasional sleep disruption
- Adults with subclinical hypothyroidism (under physician guidance)
- Athletes seeking stress-recovery and cortisol support
- Adults without liver disease, thyroid disease, or hormone-sensitive conditions
Who Should Consult a Physician First
- Pregnant or breastfeeding women: Insufficient human safety data and documented uterine-stimulating effects in animal studies
- Hyperthyroidism or Graves' disease: Ashwagandha can raise thyroid hormone levels and worsen symptoms
- Autoimmune conditions (e.g. Hashimoto's, lupus, rheumatoid arthritis): Immune-modulating effects are not well characterized in these populations
- Pre-existing liver disease or hepatotoxic medication use: Rare case reports of liver injury warrant monitoring
- Diabetes or blood pressure medication: Possible additive blood-sugar and blood-pressure-lowering effects
- Scheduled surgery: Discontinue at least 2 weeks prior due to potential effects on blood sugar and central nervous system sedation with anesthesia
- Sedative or thyroid medication users: Possible additive sedation or thyroid hormone interactions
Daily Nutra KSM-66 Ashwagandha 600mg
Better Ingredients | 100% Money Back Guarantee | 10 Years of Ancient Wisdom + Modern Science
Each serving delivers 600mg of clinically studied KSM-66® ashwagandha root extract, standardized to ≥5% withanolides — the exact form and dose used in published human clinical trials on stress, sleep, and cortisol regulation. No fillers, no proprietary blends, no leaf material. Just the root extract that works, at a dose that's been tested for safety and efficacy.
Shop KSM-66 Ashwagandha →References
- Tandon N, Yadav SS. (2020). Safety and clinical adverse effects of Ashwagandha (Withania somnifera (L.) Dunal). Journal of Ethnopharmacology. PubMed
- Bjornsson HK, et al. (2020). Ashwagandha-Induced Liver Injury: A Case Series from Iceland and the US Drug-Induced Liver Injury Network. Liver International. PubMed
- 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
- 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
- Agnihotri AP, et al. (2020). Effects of Withania somnifera supplementation on glycemic and cardiovascular risk markers: A systematic review. Journal of Ayurveda and Integrative Medicine. PubMed
- Mikolai J, et al. (2009). In vivo effects of ashwagandha (Withania somnifera) extract on the activation of lymphocytes. Journal of Alternative and Complementary Medicine. PubMed
- Sharma S, et al. (2021). A review on pharmacological and therapeutic effects of Withania somnifera. Journal of Herbal Medicine. PubMed
