Ashwagandha (Withania somnifera) is one of the most searched adaptogens in the stress and sleep space, and its side-effect profile is a genuinely important question — not an afterthought. Most of the human trial data comes from standardized root-extract products (commonly KSM-66 or Sensoril) taken for 60 days or so, at 240–600 mg per day. Here is what that research reports, and what it has not yet studied.

The short version

In the published randomized trials — mostly 8-week studies of standardized extract in healthy or stressed adults — ashwagandha has generally been reported as well tolerated, with side effects that are infrequent and usually mild. That is a reasonably reassuring track record for a widely used adaptogen. It comes with real limits, though: trials are short relative to how people actually use these products long-term, and a genuine international liver-safety signal exists that is worth taking seriously rather than downplaying.

Side effects reported in human trials

  • Mild gastrointestinal upset — the most commonly reported complaint, including nausea or stomach discomfort.
  • Drowsiness or sedation — consistent with ashwagandha's calming, non-stimulating profile; some people notice this more than others.
  • Headache or mild dizziness — reported occasionally, generally at rates not far from placebo.
  • Rare idiosyncratic liver reactions — uncommon, but documented internationally (see below).

The liver-safety signal, specifically

Regulatory and clinical reviewers in several countries have identified a small number of case reports of liver injury associated with ashwagandha use — rare, but real enough that it is tracked as an authoritative safety monograph rather than dismissed as noise. It has not been established which specific extracts, doses, or individual susceptibilities are involved, which is exactly why this is treated as a caution rather than a settled mechanism.

  • Anyone with existing liver disease should treat ashwagandha as an ingredient to discuss with a clinician first, not a default-safe adaptogen.
  • A transparent label should carry a liver-precaution line even where a given regulator (including Health Canada) does not yet formally require one — see our guide to reading a label for why voluntary disclosure matters.
  • Unusual symptoms such as jaundice, dark urine, or persistent abdominal pain warrant stopping the product and seeking medical care.

Who should check with a clinician first

  • Pregnant or breastfeeding — not studied for safety in this population; the conservative position is to avoid.
  • Liver disease, or as a general precaution given the international liver-safety signal above.
  • Thyroid disorders — ashwagandha has been studied for effects on thyroid hormone levels, which is a reason for review, not necessarily avoidance.
  • Autoimmune conditions — ashwagandha is sometimes described as an immune modulator; that mechanism warrants a conversation with a treating physician.
  • Scheduled surgery — as with many adaptogens, a conservative stop-before-surgery window is reasonable pending clinician guidance.

Interactions worth knowing about

  • Thyroid medication — potential to affect thyroid hormone levels; worth a clinician or pharmacist check.
  • Sedatives and sleep medication — possible additive drowsiness given ashwagandha's calming profile.
  • Immunosuppressants — theoretical interaction given proposed immune-modulating effects.
  • Blood-pressure or diabetes medication — some studies report modest effects on blood pressure and blood sugar, which is relevant if you are already being medically managed for either.

Where the evidence is thin

  • Long-term daily use: most trials run around 8 weeks; multi-year safety data at supplement doses is limited.
  • Children: not studied for general use; no basis for a recommendation.
  • High doses or long-duration stacking with other adaptogens: outside what has actually been tested.
  • Which specific products or extract types carry the liver-safety signal: case reports have not isolated this clearly.

Dose and quality considerations

Most positive human trials used standardized extracts — KSM-66 (root-only, the largest trial base) or Sensoril (a higher-withanolide extract at a somewhat lower milligram dose) — rather than plain root powder at an unspecified potency. A label that names the branded extract and its withanolide percentage is giving you the information needed to compare the product against the studies; "ashwagandha root powder" with no standardization tells you much less.

How to think about it

Ashwagandha's trial-reported side-effect profile is reassuring for short-term use in the populations studied — but "well tolerated in an 8-week trial of healthy adults" is a narrower claim than "safe for everyone, indefinitely." The liver-safety signal, thyroid effects, and the list of who should check first are not reasons to panic, but they are reasons to treat this as a real supplement decision rather than a risk-free one.

References

  • Salve J, Pate S, Debnath K, Langade D. "Adaptogenic and Anxiolytic Effects of Ashwagandha Root Extract in Healthy Adults: A Double-blind, Randomized, Placebo-controlled Clinical Study." Cureus, 2019;11(12):e6466. PMID: 32021735.
  • Lopresti AL, Smith SJ, Malvi H, Kodgule R. "An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: A randomized, double-blind, placebo-controlled study." Medicine (Baltimore), 2019;98(37):e17186. PMID: 31517876.
  • Chandrasekhar K, Kapoor J, Anishetty S. "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, 2012;34(3):255–262. PMID: 23439798.
  • Pratte MA, Nanavati KB, Young V, Morley CP. "An alternative treatment for anxiety: a systematic review of human trial results reported for the Ayurvedic herb ashwagandha (Withania somnifera)." Journal of Alternative and Complementary Medicine, 2014;20(12):901–908. PMID: 24805805.
  • LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. "Ashwagandha." National Institute of Diabetes and Digestive and Kidney Diseases, updated 2024. NCBI Bookshelf ID: NBK548536.