Ashwagandha side effects: what trials actually measured
Ashwagandha side effects have been measured almost entirely in short trials. A 2021 meta-analysis pooled five trials and 372 adults taking 250–600 mg a day of KSM-66 root extract — or, in one of the five, 120 mg a day of a root-and-leaf extract — for 6 to 12 weeks.[8]
A second 2021 review covered seven trials and 491 adults on 240–1,250 mg a day of extract, or 12,000 mg a day of whole-root granules in one study, for 6 to 8 weeks.[8] Across that evidence the NIH Office of Dietary Supplements describes ashwagandha as well tolerated for up to about three months and lists the common side effects as usually mild: stomach upset, loose stools, nausea and drowsiness.[8]
The reference database clinicians use for herb safety, LiverTox, puts it plainly. Side effects "are uncommon and have not been clearly defined", while large doses "can cause gastrointestinal upset, diarrhea, nausea and vomiting, probably because of direct irritation to the intestinal mucosa".[6]
Extract form and dose: what one serving actually means
Ashwagandha products differ in three ways that change what "one serving" means. The plant part comes first: extracts such as KSM-66 use the root, while others combine root and leaf, which differ chemically.[8] Then standardisation — trial products state a withanolide content, for example 15 mg of withanolides per 300 mg capsule, or 2.5% of a 500 mg tablet.[8]
Then the unit size: LiverTox records root extracts as commonly supplied at 150–600 mg per capsule or tablet, taken one to three times daily.[6]
That is also why cross-product comparison is hard: NIH says the varying preparations and doses in the research make it difficult to identify a specific extract or amount, and the same variation sits on the shelf.[8] Compare only what a label actually declares — plant part, extract quantity, standardisation, and the recommended daily portion the FSA tells you to follow.[4]
The hard limits: pregnancy, liver signs, prescription medicines
Ashwagandha carries three cautions that sit above everything else, and the first two are categorical in NHS advice on herbal medicines: you should not take them if you are pregnant or breastfeeding, or if you have kidney or liver problems.[1] The NIH fact sheet says the same about pregnancy and notes that France's food-safety agency ANSES advised against ashwagandha in pregnancy and breastfeeding in 2024.[8]
The third is the liver. Rare liver injury has been documented — covered in detail below — and the NHS instruction for its signs is unambiguous: ask for an urgent GP appointment if your skin or the whites of your eyes look yellow, which can come with itchy skin, darker pee and paler poo than usual.[2] If you take other medicines, NHS advice is to check with a pharmacist before taking a herbal product at all.[1]
Dose versus what people report
Ashwagandha's reported effects sort by dose context. Across the reviewed trials — 250–600 mg a day for 6 to 12 weeks in one analysis, 240–1,250 mg a day for 6 to 8 weeks in the other — the NIH fact sheet lists stomach upset, loose stools, nausea and drowsiness as the common effects, usually mild.[8] Large doses are where LiverTox places vomiting and diarrhoea, and the 2020 case series involved 450–1,350 mg a day.[6][7]
| Dose context | What is most often reported | Source |
|---|---|---|
| Reviewed trials: 250–600 mg/day for 6–12 weeks; 240–1,250 mg/day for 6–8 weeks | Listed as common and usually mild: stomach upset, loose stools, nausea, drowsiness | NIH ODS[8] |
| Large doses | Gut upset, diarrhoea, nausea and vomiting — probably direct irritation of the intestinal mucosa | LiverTox[6] |
| Rare: 450–1,350 mg/day taken for 1 week to 4 months | Cholestatic or mixed liver injury with jaundice and itching; one 2020 case series of five patients, liver tests normal again in 1–5 months in four of them | Björnsson 2020; NIH ODS[7][8] |
Sources: NIH Office of Dietary Supplements; LiverTox (NCBI Bookshelf); Björnsson et al., Liver International 2020. Frequencies are as described by those sources; supplement trials rarely report exact percentages.
Why shouldn't you take ashwagandha daily?
Daily ashwagandha is exactly what the trials tested: participants dosed every day for 6–12 weeks, and NIH describes the supplement as well tolerated for up to about three months.[8] The same fact sheet states plainly that evidence on use over many months or years is lacking.[8]
That is a limit on the evidence, not a demonstrated harm. It is also not the only reason to stop: NHS advice is that you should not take herbal medicines at all if you are pregnant or breastfeeding or have kidney or liver problems, and that you should check with a pharmacist first if you already take another medicine.[1]
What not to mix with ashwagandha?
Ashwagandha has five named medicine classes against it in the NIH review: thyroid hormone medicines, antidiabetes medicines, antihypertensives, immunosuppressants and sedatives.[8] The thyroid entry is the best documented — small trials recorded changes in T4 and TSH, and three case reports describe thyrotoxicosis in women taking ashwagandha extract.[8]
The NHS list for herbal products in general is wider still: statins, antidepressants, diabetes medicines such as metformin, blood-pressure medicines such as ramipril, blood thinners such as warfarin, and hormonal contraception including the combined pill. Its instruction is short — always check with a pharmacist first if you already take another medicine.[1]
What is the biggest benefit of ashwagandha?
Great Britain has authorised no health claim for ashwagandha, so no UK label — ours included — may print a benefit sentence.[3] What exists is trial data: the 2021 review covering 491 adults across seven trials measured outcomes on self-reported rating scales, and the NIH summary of that literature notes the studies used various preparations and doses, which is why it stops short of a recommendation.[8]
If you want the study-by-study picture, with effect sizes and the caveats spelled out, our guide to ashwagandha benefits goes through it properly.
What is the dark side of ashwagandha?
Ashwagandha's genuinely serious risk is rare liver injury. A 2020 case series in Liver International documented five patients — three in Iceland, two from the US Drug-Induced Liver Injury Network, three men and two women aged 21 to 62 — who developed jaundice, itching, nausea and lethargy after taking supplements containing 450–1,350 mg of ashwagandha daily for one week to four months.[7][8]
The injury pattern was cholestatic or mixed and no patient developed liver failure; liver tests normalised within one to five months in four patients, and one was lost to follow-up.[7] That series is not the whole record: LiverTox also documents eight cases from three Indian hospitals between 2019 and 2022, three of them fatal in people with existing liver disease, and cites an analysis counting 23 reported cases of clinically apparent ashwagandha liver injury in the literature.[6]
LiverTox rates ashwagandha a likelihood score of B — a "likely cause of clinically apparent liver injury". It describes the typical course as mild-to-moderate and self-limited, while noting that fatal cases due to acute liver failure have been described.[6] Rare does not mean impossible: know the warning signs, and act on them early.
What happens if I take ashwagandha every day?
Taking ashwagandha every day is the pattern the trials ran: 6 to 12 weeks of continuous dosing, at 250–600 mg a day of KSM-66 root extract in the pooled analysis, and NIH describes that use as well tolerated for up to about three months.[8] The effects it lists as common are the mild ones in the table above: stomach upset, loose stools, nausea, drowsiness.[8]
Trial doses are not product doses, and the FSA's advice on supplements is simply to read the label and follow its instructions, including the recommended daily dosage.[4] LiverTox notes that large doses can cause gastrointestinal upset, diarrhoea, nausea and vomiting, probably through direct irritation of the intestinal mucosa.[6]
Why do I feel weird after taking ashwagandha?
NIH lists four common effects of ashwagandha, all usually mild: stomach upset, loose stools, nausea and drowsiness.[8] Drowsiness is the one people notice during the day. For the digestive three, check the daily dose against the 250–600 mg of extract used in the pooled trials, and follow the timing on the product's own label.[8][4] An unexpected symptom that is not on that list is a reason to stop and ask a pharmacist or GP, not to push on.
One cluster is different: yellow skin or eyes, itchy skin, darker pee and paler poo than usual. That is the NHS description of jaundice, and its instruction is to ask for an urgent GP appointment or contact NHS 111 rather than wait it out.[2]
What happens if a woman takes ashwagandha?
The NIH fact sheet does not give sex-stratified figures for adverse effects, so its list applies to men and women alike.[8] Two entries in it are specific to women: three case reports of thyrotoxicosis in women aged 32 to 73 taking ashwagandha extract, which resolved when they stopped, and the advice against use in pregnancy and while breastfeeding.[8] NHS advice on herbal medicines says the same about pregnancy and breastfeeding.[1]
Searches for "ashwagandha side effects for female" often trace back to menstrual-cycle anecdotes on forums. The NIH fact sheet lists no menstrual-cycle outcome among the effects it reports, so there is nothing here to confirm or deny one.[8]
Who should avoid using ashwagandha?
Ashwagandha is not for everyone, and two of the exclusions come straight from NHS advice on herbal medicines: do not take them in pregnancy or while breastfeeding, and avoid them if you have kidney or liver problems.[1]
NIH adds two more — some experts advise against ashwagandha for men with hormone-sensitive prostate cancer, and it may interact with thyroid, diabetes, blood-pressure, immunosuppressant and sedative medicines.[8] Stop and ask for an urgent GP appointment if your skin or the whites of your eyes turn yellow.[2]
A UK-specific point worth knowing: food supplements are regulated as food, and the FSA's guidance says that if you are concerned about the safety, labelling or claims of a food supplement you should report it to your local authority or district council.[4] The MHRA's Yellow Card scheme covers medicines, vaccines, medical devices, blood products and e-cigarettes.[5] If you are unsure which route fits, ask your pharmacist or GP.
- Across the reviewed trials — 250–600 mg/day for 6–12 weeks, 240–1,250 mg/day for 6–8 weeks — the common ashwagandha side effects are listed as usually mild: stomach upset, loose stools, nausea, drowsiness.
- LiverTox attributes gut upset, diarrhoea, nausea and vomiting to large doses — stay with the dose on the label.
- Rare liver injury is documented: one 2020 case series of five patients at 450–1,350 mg/day taken for one week to four months, and LiverTox records further cases since.
- NHS advice: do not take herbal medicines in pregnancy or while breastfeeding, or with kidney or liver problems; on any other medicine, check with a pharmacist first.
- Yellow skin or eyes, itchy skin, darker pee, paler poo: NHS advice is an urgent GP appointment or NHS 111, not waiting it out.
- Concerns about a food supplement go to your local authority under FSA guidance; Yellow Card covers medicines, vaccines, devices, blood products and e-cigarettes.
If you are comparing formats across our gummy vitamins range, our KSM-66 ashwagandha gummies, 2500 mg per serving print the ashwagandha figure per two-gummy daily serving on the label — the number this article suggests you look for on any product.
Related reading
Start with our guide to what ashwagandha research actually measures, which covers the trials, the effect sizes and why UK labels stay silent about them.
References
- NHS. Herbal medicines and complementary therapies. link
- NHS. Jaundice. link
- Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. GOV.UK. link
- Food Standards Agency. Food supplements guidance. GOV.UK. link
- Medicines and Healthcare products Regulatory Agency. Yellow Card scheme — what you can report. link
- LiverTox: Clinical and Research Information on Drug-Induced Liver Injury — Ashwagandha. NCBI Bookshelf, National Institute of Diabetes and Digestive and Kidney Diseases, last updated 3 December 2024. link
- Björnsson HK, Björnsson ES, Avula B, et al. Ashwagandha-induced liver injury: a case series from Iceland and the US Drug-Induced Liver Injury Network. Liver International. 2020;40(4):825–829. link
- Office of Dietary Supplements (NIH). Ashwagandha — Health Professional Fact Sheet. Accessed September 2026. link