Does ashwagandha carry liver, gut, or thyroid risks?

Does ashwagandha carry side effects serious enough to change how you use it? The herb, Withania somnifera — sold widely for stress and sleep — looks tolerable in most short-term research. But “natural” does not equal harmless. The evidence clusters around nausea, diarrhea, vomiting, and drowsiness on the common end. At the rarer end sits a liver-injury signal that has drawn real clinical attention, plus a smaller thyroid-related caution. Neither gets the clear coverage it deserves in most supplement guides.

That distinction matters. Safety questions about supplements tend to collapse into two bad answers: either the product is safe because it comes from a plant, or it is dangerous because case reports exist. Ashwagandha sits in the messier middle. The best read on the evidence right now: most healthy adults in shorter studies do not seem to develop major problems, but the downside cases that have appeared in the literature are specific enough to take seriously. This is especially true for anyone with liver disease, a thyroid disorder, or a medication list that includes sedatives.

What side effects show up most often?

The most consistent short-term complaints split into two buckets: gastrointestinal and neurologic. Both the NIH Office of Dietary Supplements and the National Center for Complementary and Integrative Health list stomach upset, diarrhea, vomiting, and drowsiness as known side effects. NCCIH states it plainly: “In some individuals, ashwagandha preparations may cause drowsiness, stomach upset, diarrhea, and vomiting.”

A 2026 safety overview from Herbal Reality highlighted a 12-month prospective observational study in Phytotherapy Research covering 191 participants. Investigators logged 18 mild adverse events — mostly nausea, digestive upset, and headache — with no liver, kidney, or thyroid changes emerging over that follow-up window. Read straightforwardly, the ordinary side-effect profile is more about tolerance than toxicity.

But “mild” is not the same as trivial. Someone taking ashwagandha for sleep may notice next-day grogginess more than a trial’s adverse-event table captures. Someone with a sensitive stomach may quit long before hitting any study endpoint. Supplement research also lumps together extracts that differ in standardization, dose, and manufacturing quality. The common side effects are the easy part of the answer. They are not the whole answer.

Why liver risk gets more attention

In 2025, Yotam Ronen and colleagues reported in Frontiers in Nutrition that after screening 1,396 publications, 97 percent of the ashwagandha literature raised no toxicity concerns. Even so, the review still identified nine liver-toxicity papers and one thyroid-related signal. The overall literature does not suggest routine severe harm. But the red-flag events are concentrated in organs where harm matters most.

In 2023, Cyriac A. Philips and colleagues described in Hepatology Communications 23 patients with ashwagandha-induced liver injury in India between 2019 and 2022, including eight cases tied to single-ingredient ashwagandha products. The paper’s central finding is cholestatic hepatitis: inflammation and impaired bile flow that can produce jaundice, dark urine, itching, and fatigue. Philips and coauthors also cautioned that people with pre-existing liver disease may fare worse than otherwise healthy users.

Case-series evidence is not the same as a randomized trial. Supplement attribution is messy: labels can be wrong, formulations vary, and users may be taking more than one product. Still, the liver signal is stronger than a one-off anecdote. A later 2026 literature review counted 37 reported cases and found jaundice in 78 percent of patients and pruritus, meaning itch, in 51 percent. Those numbers do not tell readers that liver injury is common. They tell readers what kind of harm to look for if symptoms appear.

What about thyroid and hormone effects?

The thyroid question is less dramatic than the liver question, but it is not imaginary. Thyroid hormones regulate metabolism, heart rate, and temperature. Even a modest interaction matters if someone already has a thyroid disorder or takes prescription hormone. In 2025, Thomas Brendler and coauthors examined in Phytotherapy Research whether ashwagandha shows biologic activity that could matter for hormone-sensitive systems. Combined with the single thyroid signal noted in Ronen’s 2025 review, that is enough to move the issue from internet myth to cautious uncertainty.

The practical reading is not that ashwagandha routinely damages the thyroid. It is that people with hyperthyroidism, fluctuating thyroid labs, or thyroid medication have reason to be more careful than a healthy adult browsing a sleep-supplement aisle. The same applies to anyone stacking ashwagandha with other sedating products. When a supplement can cause drowsiness on its own, interaction risk is part of the safety profile, not a footnote. Any reader with thyroid disease, active liver disease, or a complicated medication list should consult a doctor before starting any supplement.

What the evidence still cannot tell you

Supplement explainers often go wrong here. They take an incomplete evidence base and turn it into fake certainty. Ashwagandha research remains patchy on product standardization, long-term exposure, and who is most vulnerable to rare adverse events. A capsule standardized to one set of withanolides does not automatically match a powder, tincture, or multi-herb blend. A mild side-effect table from a controlled study also does not overwrite the significance of post-marketing case reports. Those reports are often how rare harms first become visible.

So what is the honest bottom line? For most users, the evidence still points first to mild gut symptoms or sleepiness, not to a high probability of severe toxicity. But the rare liver-injury cases are specific enough to treat as real. The thyroid question is unresolved enough to justify caution rather than dismissal. Readers should be more skeptical of marketing that presents ashwagandha as universally gentle than of clinicians who say the herb may be reasonable for some people and a bad fit for others.

What to watch next is straightforward: better long-term trials with standardized products, clearer tracking of liver events, and more direct work on thyroid outcomes in people already at risk. Until then, the safest evidence-based answer is neither panic nor hype. Ashwagandha’s side effects usually look mild. But its liver, gut, and thyroid caveats deserve to be part of the conversation before anyone treats it like a no-risk daily habit.

References

1. Ronen Y, et al. Comprehensive safety evaluation of Withania somnifera (Ashwagandha): an AI-driven meta-analysis and quantitative structure-activity relationship based toxicity assessment. Frontiers in Nutrition. 2025. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1658265/full
2. Philips CA, et al. Ashwagandha-induced liver injury: a case series from India and literature review. Hepatology Communications. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC10531359/
3. Brendler T, et al. Evaluation of potential hormonal activities of Ashwagandha (Withania somnifera). Phytotherapy Research. 2025. https://pubmed.ncbi.nlm.nih.gov/41454558/