Ashwagandha side effects: who shouldn't take it
What the latest trials show about ashwagandha's side effects, the rare liver risk, its effects on thyroid and hormones, and who shouldn't take it.
- Written by
- Amy D.
- Last updated
- Reading time
- 8 min read
Overview
Ashwagandha's side effects are usually mild: stomach upset, headache and drowsiness, and in trials they were about as common as on a placebo. The rare serious risk is liver injury. Don't take it if you're pregnant, breastfeeding, under 18 or have liver disease, and ask your GP first if you have a thyroid condition or take regular medicines.
Key points
- Common: mild stomach upset, headache and drowsiness, about as often as on a placebo.
- Liver: injury is rare, and most people in published cases recovered after stopping.
- Thyroid: it can shift thyroid hormone, so ask your GP if you have a thyroid condition.
- Avoid it: if pregnant, breastfeeding, under 18 or with liver disease.
- Medicines: interactions are possible, so check with your GP or pharmacist first.
What are the side effects of ashwagandha?
The most common are stomach upset, headache and drowsiness, and they're usually mild [1][5]. In trials, they were about as common on ashwagandha as on a dummy pill [1][2][3].
Stomach upset covers nausea, indigestion and loose stools [1]. A 2026 review of 23 trials in 2,317 healthy adults found none that were serious. People took 125 to 600 mg of root extract a day for up to 6 months [1].
| Study | People | Dose and length | Side effects | Evidence |
|---|---|---|---|---|
| Coope 2026, review [1] | 23 trials, 2,317 healthy adults | 125 to 600 mg a day, up to 180 days | Mild and infrequent, and seen on placebo too; none serious | Moderate |
| Pakhale 2026 [2] | 1,002 adults with high stress scores | 600 mg a day for 8 weeks | 5.2% of people on ashwagandha and 7.8% on placebo; none serious | Moderate |
| Chopra 2026 [3] | 1,200 healthy adults | 500 mg a day for 24 weeks | Mostly mild and gut-related; nobody stopped because of them | Moderate |
The 24-week trial was run by Indian government researchers, not a supplement company, and it found the same [3].
Is ashwagandha safe?
For most healthy adults, yes, at least in the short term. The US National Institutes of Health says it may be safe for up to 3 months, and that there isn't enough information on longer use [5]. Trials of up to 6 months found few problems [1][3].
The rare serious risk is liver injury, covered below, and some people shouldn't take it at all. In the UK it's sold as a food supplement. The Food Standards Agency is reviewing its safety with its Committee on Toxicity [10].
Does ashwagandha make you sleepy?
It can, but not often. Drowsiness is a known side effect [5]. Yet in the largest safety trial, nobody on ashwagandha reported it, against 2 people on a placebo [2].
In the 24-week trial, tiredness was no more common than on a placebo either [3]. France's food safety agency still advises against taking it before you drive or use machines, as some people in trials felt sleepy [6]. If it makes you drowsy, take it in the evening.
Can ashwagandha damage your liver?
Rarely, but it has happened. A 2026 review found 25 published cases of liver injury linked to ashwagandha. It usually began weeks after starting, with yellow skin or eyes, itching and dark urine [4].
Most people recovered: 20 of the 25 got better after stopping, usually within 1 to 5 months. Three died, all of whom already had cirrhosis, and one needed a liver transplant [4]. Nobody knows how often it happens, because nobody knows how many people take ashwagandha [4].
In trials, liver tests stayed normal in 9 studies of 1,578 healthy adults [1]. In the 24-week trial, mild rises in liver enzymes showed up in 6 of 598 people on ashwagandha and 3 of 602 on a placebo Early [3].
Does ashwagandha affect your thyroid?
It can. In trials of healthy adults, thyroid hormone levels didn't change [1]. Pooling 23 trials, though, one thyroid hormone, T4, rose slightly Mixed [7].
In a small trial of 50 adults with a slightly underactive thyroid, 600 mg a day for 8 weeks raised thyroid hormone levels more than a placebo Early [9]. Four people have also been reported with too much thyroid hormone while taking ashwagandha, and all improved after stopping [8].
So if you have a thyroid condition or take thyroid medicine, ask your GP before taking ashwagandha [5][6].
Ashwagandha side effects for men and women
In men, ashwagandha tends to raise testosterone a little. Across trials it rose by about 57 ng/dL on average Moderate [7], and stayed within the normal range [1]. That's why people with hormone-sensitive prostate cancer are advised to avoid it [5].
In women, pooled trials found no significant change in testosterone or oestradiol, the main form of oestrogen [7]. France's food safety agency advises people with high male hormone levels, such as some women with polycystic ovary syndrome (PCOS), not to take it [6].
Who shouldn't take ashwagandha?
Official advice from the US and France names several groups who should avoid it [5][6]. No UK body has published its own list yet.
| Who | Advised by |
|---|---|
| Pregnant or breastfeeding women | US and France [5][6] |
| Children and teenagers under 18 | France [6] |
| People with liver disease | France [6] |
| People with a thyroid condition | US and France [5][6] |
| People with a heart condition | France [6] |
| People with an autoimmune condition | US [5] |
| Anyone with surgery planned | US [5] |
| Men with hormone-sensitive prostate cancer | US [5] |
Does ashwagandha interact with medicines?
It might. US health advice lists medicines for diabetes, blood pressure and the thyroid, plus sedatives, epilepsy medicines and medicines that damp down the immune system [5].
These interactions are possible rather than proven: lab results are mixed, and no study in people has measured one [6]. If you take any regular medicine, ask your GP or pharmacist before adding ashwagandha.
Can you drink alcohol with ashwagandha?
No study has tested the two together, so nobody knows for sure. Alcohol was a factor in some of the published liver cases [4], and both can make you drowsy. Keep alcohol low while you take it.
How much ashwagandha is safe?
There's no official upper limit. France's food safety agency says a safe level can't be set yet, because the extracts in studies aren't described well enough [6].
Trials have used 125 to 600 mg of root extract a day, and side effects didn't rise with the dose in that range [1]. Stick to the dose on the label; our ashwagandha guide covers what each dose has been tested for.
Where Nooroots fits
Nooroots Ashwagandha + Lion's Mane gives you 120 mg of KSM-66 and 500 mg of lion's mane extract in two caffeine-free capsules a day. It's made for calm focus and calm resilience on demanding days.
KSM-66 is a root-only extract standardised to 5% withanolides, the type of extract the 2026 safety review looked at. It was used in 16 of that review's 23 trials [1].
Frequently asked questions
Does ashwagandha cause headaches?
Occasionally. In the largest safety trial, headache affected 0.2% of people on ashwagandha and 2.2% on a placebo [2].
What are the side effects of Withania somnifera?
The same as ashwagandha's, because Withania somnifera is its botanical name. The usual ones are mild stomach upset, headache and drowsiness in a small number of people [1].
Is ashwagandha banned in the UK?
No. It's sold as a food supplement in the UK, and the Food Standards Agency is reviewing its safety with its Committee on Toxicity [10]. Our ashwagandha guide has the latest UK and EU position.
What are the pros and cons of ashwagandha?
On the plus side, trials have found root extracts improved sleep quality and lowered cortisol, the main stress hormone, as our ashwagandha guide explains. The downsides are mild side effects in a few people, a rare liver risk and the groups who shouldn't take it [1][4][5].
Can you take ashwagandha with L-theanine?
No study has tested the two together, and no interaction is known. Our L-theanine guide compares them.
Can you take ashwagandha with lion's mane?
Yes. No interaction is known, though no trial has tested them together; see lion's mane and ashwagandha: can you take them together?
References
Every study here is listed so you can read it yourself. This guide is for general information and doesn't replace advice from your GP or pharmacist. We review it when new research is published.
- Coope OC et al. (2026). Back to the roots: safety and tolerability of standardised ashwagandha (Withania somnifera) root extract in healthy adults. A systematic review of biomarkers and adverse events. Pharmaceuticals 19(5): 725. PMID 42198398
- Pakhale K et al. (2026). Safety of 8-week administration with ashwagandha (Withania somnifera) root extract in adults with stress and anxiety: findings from a prospective, randomized, multi-center, double-blinded, placebo-controlled study. Phytotherapy Research 40(8): 5005–5015. PMID 41943502
- Chopra A et al. (2026). Safe prolonged prophylactic use and tolerability of Ashwagandha following COVISHIELD vaccination over 24 weeks: a multicentre randomized double-blind placebo-controlled trial. Frontiers in Medicine 13: 1852954. doi:10.3389/fmed.2026.1852954
- McIntyre D et al. (2026). Ashwagandha (Withania somnifera)-associated liver injury: a scoping review of clinical characteristics and safety considerations. Cureus 18(5): e109764. PMID 42367407
- National Center for Complementary and Integrative Health (updated March 2023). Ashwagandha: usefulness and safety. US National Institutes of Health. nccih.nih.gov/health/ashwagandha
- Anses (2024). Avis relatif aux risques liés à l'utilisation des préparations de Withania somnifera (L.) Dunal dans les compléments alimentaires (opinion 2021-SA-0077, in French). French Agency for Food, Environmental and Occupational Health and Safety, 19 April 2024. anses.fr
- Fornalik M et al. (2026). Hormonal modulation with Withania somnifera: systematic review and meta-analysis of randomized-controlled trials. Planta Medica 92(8): 790–805. PMID 41740946
- Vollmer G, Brendler T (2026). Evaluation of potential hormonal activities of ashwagandha (Withania somnifera). Phytotherapy Research 40(8): 4880–4897. PMID 41454558
- Sharma AK et al. (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 24(3): 243–248. PMID 28829155
- Food Standards Agency (25 June 2026). Summary of responses to call for evidence on ashwagandha. GOV.UK. gov.uk/government/consultations
