What are the biggest side effects of ashwagandha?
Ashwagandha has a reputation as a gentle adaptogen — and in most clinical trials, that reputation holds. The biggest side effects are usually mild: stomach upset, drowsiness, and occasional headache. The problem is that "usually" is not the same as "always." A smaller set of people report thyroid shifts, hormone changes, or, in rare published case reports, liver injury. Understanding which effects are common, which are uncommon, and which belong to high-dose or poorly characterized extracts is the difference between using ashwagandha well and using it blindly.
Most ashwagandha side effects show up as mild digestive discomfort or sedation — not dramatic reactions — which is why they are easy to miss and easy to overstate.
Ashwagandha (Withania somnifera) is one of the most studied herbs in modern clinical literature, and safety data is no longer anecdotal. In the landmark 60-day randomized trial of a high-concentration full-spectrum root extract, adverse events were mild and comparable to placebo, with no serious events reported. (1) That pattern repeats across later KSM-66 and related root-extract trials: GI discomfort and sleepiness appear, but they rarely force people to stop.
What has changed is the volume of use. Millions of people now take ashwagandha in capsules, gummies, powders, and stacked "stress formulas." When an herb scales that fast, rare events that never show up in a 64-person trial start appearing in case reports — especially liver injury and thyroid overstimulation in susceptible people. Those reports do not cancel the trial data. They do mean the safety conversation has to be more precise than "it's natural, so it's safe."
A 2021 randomized, double-blind, placebo-controlled study of KSM-66 in healthy adults found the extract was well tolerated over 8 weeks, with laboratory safety markers remaining within normal limits and adverse events not meaningfully different from placebo. (2) That is the clinical baseline: standardized root extract, studied doses, generally clean labs.
Form still matters. KSM-66 is a root-only extract produced by a milk-based process, standardized to at least 5% withanolides, and used in more than 24 human trials. Generic "ashwagandha" on a label can mean leaf, whole plant, unstandardized powder, or a solvent extract with a completely different withanolide profile. Side-effect risk is not identical across those products.
This article breaks down the biggest ashwagandha side effects by how often they actually appear, how the herb works in the body, what the clinical data shows, how to dose a standardized extract, and who should skip it or talk to a physician first.
What Is KSM-66 Ashwagandha?
Withania somnifera, known in Ayurveda as ashwagandha or Indian ginseng, is classified as a rasayana — a rejuvenative herb traditionally used for vitality, stress resilience, and recovery. The root is the historically used part. The primary bioactive compounds are withanolides, a family of steroidal lactones that appear to modulate stress physiology rather than act as a stimulant or sedative in the conventional drug sense.
Those withanolides are why two bottles that both say "ashwagandha" can behave differently. An unstandardized powder may contain trace withanolides. A leaf-containing extract can carry a different compound mix than root-only material. Side effects tracked in human trials are almost always tied to a specific extract, dose, and duration — not to the plant name on the front of the bottle.
KSM-66 is a full-spectrum, root-only ashwagandha extract standardized to ≥5% withanolides. It is produced without chemical solvents, using a process that includes milk, and it is the extract used in a large share of the modern human trials on stress, sleep, cortisol, cognition, and physical performance. When this article discusses clinical safety, it is referring to that class of standardized root extract unless a case report clearly involves something else.
How KSM-66 Ashwagandha Works: Why Side Effects Follow the Same Pathways
Ashwagandha's benefits and its side effects travel on the same biological roads. The herb is best understood as an HPA-axis modulator with secondary effects on sleep architecture, thyroid hormone conversion, and gastrointestinal motility.
Under chronic stress, the hypothalamus releases corticotropin-releasing hormone, the pituitary gland secretes ACTH, and the adrenal cortex pours out cortisol. Withanolides appear to dampen this cascade, which is why serum cortisol falls in several trials and why people often feel calmer. (1) The same calming signal can show up as drowsiness, vivid dreams, or a heavier evening "drop" if the dose is large or taken on an empty stomach.
In the gut, ashwagandha can irritate a sensitive stomach the way many bitter, concentrated botanicals do. That is the most common complaint: nausea, cramping, loose stool, or a metallic aftertaste, especially in the first one to two weeks.
At the thyroid, some data suggest ashwagandha can increase T3 and T4 in people with subclinical hypothyroidism. (3) For someone with low thyroid function that may be useful. For someone already on levothyroxine, or with a history of hyperthyroidism, that same pathway is a reason to involve a clinician — not a reason to self-experiment.
The rarest pathway in the published record is hepatic. A small number of case reports describe ashwagandha-associated liver injury, typically with jaundice and a cholestatic or mixed enzyme pattern after weeks to months of use. (4) These events are uncommon relative to how widely the herb is used, and they have not been a signal in placebo-controlled KSM-66 trials. They are still the side effect that deserves the most respect.
Withanolides act on the HPA axis first; digestive discomfort and sedation are the common offshoots, while thyroid and liver effects are less frequent and more person-specific.
What the Clinical Research Shows
The most common side effects: GI upset and drowsiness
In Chandrasekhar, Kapoor, and Anishetty's 2012 randomized, double-blind, placebo-controlled trial (Indian Journal of Psychological Medicine, n=64, 300 mg twice daily for 60 days), a high-concentration full-spectrum ashwagandha root extract reduced perceived stress and serum cortisol versus placebo. Adverse events were described as mild and transient, and they did not differ in a clinically concerning way from placebo. No serious adverse events occurred. (1)
Salve, Pate, Debnath, and Langade (2019) tested 250 mg and 600 mg daily of KSM-66 for 8 weeks in stressed adults. Both doses improved stress scores; the 600 mg dose produced a larger cortisol reduction. Tolerability remained high, with the expected mild complaints rather than a dose-limiting toxicity signal. (5) Across this literature, the "biggest" side effects in the everyday sense are still nausea, abdominal discomfort, loose stools, sleepiness, and headache.
Sleepiness, vivid dreams, and next-day grogginess
Langade, Kanchi, Salve, Debnath, and Ambhore (2019) evaluated KSM-66 300 mg twice daily for 10 weeks in adults with insomnia. Sleep onset, sleep quality, and anxiety scores improved versus placebo. (6) That sedative-leaning effect is a benefit for night-time use and a side effect for people who take a large dose before a meeting. A minority of users also report vivid dreams. These effects typically track evening dosing and often settle after the first two weeks.
Thyroid hormone changes — uncommon, but real in the right population
Sharma, Basu, and Singh (2018) studied 600 mg/day of ashwagandha root extract for 8 weeks in patients with subclinical hypothyroidism (Journal of Alternative and Complementary Medicine, n=50). Serum TSH fell, and T3 and T4 rose significantly versus placebo, with the extract described as safe and well tolerated in that cohort. (3) That is not a typical side effect in euthyroid adults in short trials. It is a physiologically plausible effect that becomes a risk if you already have Graves disease, uncontrolled hyperthyroidism, or a thyroid medication that has not been rechecked.
Hormone and reproductive effects in men
Lopresti, Drummond, and Smith (2019) gave overweight men 600 mg/day of ashwagandha extract for 8 weeks and observed increases in DHEA-S and testosterone versus placebo, alongside a reduction in fatigue. (7) For many men, that is a desired outcome. It is still a systemic hormone shift. People with hormone-sensitive prostate conditions, those on testosterone therapy, or anyone told to avoid androgenic supplements should not treat ashwagandha as hormonally inert.
Rare but serious: liver injury case reports
Björnsson, Björnsson, and colleagues have documented ashwagandha-associated liver injury in case series, with latency often in the range of weeks to several months and a mixed or cholestatic biochemical pattern. (4) Complementary reviews in the hepatology literature reach the same conclusion: the events are rare, often reverse after stopping the product, and are hard to pin on a single branded extract because many commercial products are multi-ingredient or poorly labeled. (8)
This is the side effect that should change behavior even though it is not the most common. New unexplained fatigue, dark urine, pale stools, itching, or yellowing of the skin or eyes means stop the supplement and get liver tests — do not "push through" another bottle.
What the dedicated safety trials actually measured
Verma, Thakur, and colleagues (2021) assessed KSM-66 300 mg twice daily for 8 weeks in healthy adults, tracking hematology, liver enzymes, kidney function, and thyroid markers. The extract was well tolerated; laboratory values stayed within reference ranges and adverse events were similar to placebo. (2) Tandon and Yadav's broader clinical review of ashwagandha root similarly characterizes the human safety record as favorable at studied doses, while noting that pregnancy, autoimmune disease, and concurrent thyroid or sedative medication still warrant caution. (9)
Dosage, Form, and What to Look For on the Label
Across the human clinical trial literature, the effective dose range for KSM-66 is 300–600 mg per day, typically taken as a single evening dose or split morning and evening. Most trials ran for 8–12 weeks, with participants reporting meaningful stress or sleep changes beginning at 2–4 weeks. Side effects, when they occur, cluster in the first 14 days and at the 600 mg end of the range, especially on an empty stomach.
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 300 mg per serving; 600 mg matches several key human trials
- Third-party tested (NSF, Informed Sport, or equivalent)
Avoid products that simply list "ashwagandha" without specifying a standardized root extract — these products typically contain inconsistent amounts of withanolides, may include leaf material, and will not replicate the safety or efficacy profile documented in published KSM-66 trials. Stacked formulas that hide the milligram amount inside a proprietary blend make it impossible to know whether you are taking a studied dose or an unstudied megadose.
Safety Profile and Side Effects
KSM-66 has an excellent safety profile across clinical trials. At the doses studied (300–600 mg/day), it is well tolerated, with no significant excess of adverse events versus placebo in trials up to 12 weeks. That is the evidence-based headline. The fine print is that "well tolerated" still includes a short list of effects you should expect to possibly feel, plus a shorter list you should never ignore.
Mild side effects reported in a minority of participants include:
- Gastrointestinal upset — nausea, cramping, or loose stool, most often if taken on an empty stomach
- Mild sedation or grogginess — particularly with evening or high-end 600 mg dosing; often useful for sleep, inconvenient in the morning
- Headache — usually early in use and self-limited
- Vivid dreams — uncommon, typically tied to night-time dosing
- Transient appetite or stool changes during the first two weeks
Less common effects that deserve a lower threshold for stopping and calling a clinician:
- Thyroid symptoms — palpitations, heat intolerance, unexplained anxiety, or tremor, especially if you already have thyroid disease
- Liver warning signs — jaundice, dark urine, persistent upper-right abdominal pain, severe fatigue, or itching
- Paradoxical agitation or insomnia — uncommon, but a reason to lower the dose or discontinue
Take with food or a small snack to minimize GI sensitivity, especially during the first two weeks. If sedation is too strong, move the capsule to the evening. If you need thyroid or liver labs for another reason, it is reasonable to include them after several weeks of use rather than assuming an herbal extract cannot move those numbers.
Ashwagandha is not established as safe in pregnancy or breastfeeding and is traditionally avoided in those states. It may theoretically enhance the effects of sedatives, thyroid hormone, and immunosuppressants. None of those interactions are a reason for healthy adults at clinical doses to panic. They are a reason to treat ashwagandha as a pharmacologically active extract — because that is what the trials show it is.
Who Should — and Shouldn't — Take KSM-66
Ideal Candidates
- Adults with chronic stress who want a root extract actually used in human cortisol trials
- People whose main complaint is wired-and-tired sleep, and who can take the dose in the evening
- Athletes and high-output professionals looking for studied 300–600 mg dosing rather than a mystery blend
- Adults who have already ruled out red-flag symptoms (jaundice, uncontrolled thyroid disease, pregnancy)
Who Should Consult a Physician First
- Thyroid disease or thyroid medication: Ashwagandha can raise T3/T4 in subclinical hypothyroidism; doses and labs may need adjustment. (3)
- History of liver disease or unexplained enzyme elevations: Rare hepatotoxicity case reports make this a stop-and-ask situation, not a DIY experiment. (4)
- Pregnancy or breastfeeding: Human safety is not established; do not use.
- Autoimmune conditions: Ashwagandha may stimulate immune activity; people with RA, lupus, or similar conditions should get individualized advice.
- Hormone-sensitive conditions or testosterone therapy: Clinical data show androgen-related marker changes in some men. (7)
- Sedative, anxiolytic, or immunosuppressive medication: Additive effects are plausible; coordinate with the prescribing clinician.
- Surgery: Because of possible CNS and immune effects, many clinicians advise stopping herbal adaptogens 1–2 weeks before elective procedures.
The biggest side effects of ashwagandha, in order of how often people actually feel them, are stomach upset and sleepiness. The biggest side effects in terms of medical seriousness are thyroid overstimulation in susceptible people and rare liver injury. A standardized root extract such as KSM-66 does not erase those possibilities. It does put you on the same form, dose, and evidence base as the trials that found the herb generally safe.
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, cortisol reduction, and sleep. No fillers, no proprietary blends. Just the root extract that works.
Shop KSM-66 Ashwagandha →References
- 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
- Verma N, Gupta SK, Tiwari S, Mishra AK. (2021). Safety of Ashwagandha Root Extract: A Randomized, Placebo-Controlled Study in Healthy Volunteers. Complementary Therapies in 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
- Björnsson HK, Björnsson ES, Avula B, Khan IA, Jonasson JG, Ghabril M, Hayashi PH, Navarro V. (2020). Ashwagandha-induced liver injury: A case series from Iceland and the US Drug-Induced Liver Injury Network. Liver International. PubMed
- 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
- Langade D, Kanchi S, Salve J, Debnath K, Ambhore D. (2019). Efficacy and Safety of Ashwagandha (Withania somnifera) Root Extract in Insomnia and Anxiety: A Double-blind, Randomized, Placebo-controlled Study. Cureus. PubMed
- Lopresti AL, Drummond PD, Smith SJ. (2019). A Randomized, Double-Blind, Placebo-Controlled, Crossover Study Examining the Hormonal and Vitality Effects of Ashwagandha (Withania somnifera) in Aging, Overweight Males. American Journal of Men's Health. PubMed
- Lubarska M, Hałasiński P, Hryhorowicz S, Mahadea DS, Lykowska-Szuber L, Eder P, Dobrowolska A, Krela-Kaźmierczak I. (2023). Liver Dangers of Herbal Products: A Case Report of Ashwagandha-Induced Liver Injury. International Journal of Environmental Research and Public Health. PubMed
- Tandon N, Yadav SS. (2020). Safety and clinical effectiveness of Withania somnifera (Linn.) Dunal root in human ailments. Journal of Ethnopharmacology. PubMed
