What Are the Side Effects of Ashwagandha? What the Trials Show

In trials, ashwagandha's side effects were mild and about as common as on placebo: stomach upset, nausea, headache and drowsiness. In the largest, an industry-funded trial of 1,002 adults, 28 adverse events were logged among 498 people on 600 mg a day (5.6%) and 46 among 504 on placebo (9.2%). Rarer and more serious: 25 published cases of liver injury and three of an overactive thyroid.^{1, 2, 3} Part of the Wellgard ashwagandha guide.

Evidence at a glance

• Trials: 23 safety trials in 2,317 healthy adults, at 125 to 600 mg a day for up to 180 days, pooled in 2026.¹
• Largest single trial: 1,002 adults on 600 mg a day or placebo for 8 weeks; industry-funded.²
• Strongest measured outcome: adverse events, 28 among 498 people on ashwagandha (5.6%) against 46 among 504 on placebo (9.2%), none serious.²
• Not tested: side-effect rates for women and men separately; people with kidney disease; no pooled trial ran beyond 180 days.

Sources checked on 13 October 2026.

What are the most common side effects of ashwagandha?

Stomach upset, nausea, headache and drowsiness, mostly mild and recorded on placebo too. A 2026 review of 23 trials, by a team that included two authors from UK supplement companies, found gastrointestinal discomfort, headache and transient drowsiness infrequent and in both groups, no serious events attributable to the extract, and liver, kidney, blood, hormone and heart markers within normal ranges.¹ The largest trial, industry-funded on an extract its maker supplied, gives rates.²

In 80 healthy adults on 600 mg a day for 8 weeks, no adverse events were reported.⁴ A 12-month study of 191 adults, with no placebo group, recorded 18 mild events, all settling untreated.⁵

Are the side effects different for women and men?

The trials here did not report side effects by sex; the 80-person trial enrolled 40 women and 40 men and recorded none in either.⁴ Women: ashwagandha must not be taken in pregnancy or while breastfeeding, when the NHS says not to take herbal medicines; no study has measured it in breast milk, and hormonal contraception is on the NHS list of medicines that may not mix well with herbal medicines.^{6, 7} The women-only trials are in ashwagandha for women. Men: testosterone rose by about 57 ng/dL in men across pooled trials, inside the normal range, and a US drug reference advises caution for men with hormone-sensitive prostate cancer, who should ask their specialist first.^{1, 7, 8}

What does ashwagandha do to the liver?

In 25 published cases, it injured it. A review to December 2025 found them in 13 publications: injury after weeks of use, mostly cholestatic, with jaundice and itching; most recovered over weeks to months after stopping; one needed a transplant; three died, all with existing cirrhosis.³ Of eight Indian patients on single-ingredient products, five had chronic liver disease; three of them developed acute-on-chronic liver failure and died.⁹ The safety trials enrolled healthy adults, so no study gives a rate. The review's authors advise people with advanced chronic liver disease to avoid it.³ For yellow skin or eyes, with itching, darker urine or paler stools, the NHS says: "Ask for an urgent GP appointment or get help from NHS 111".¹⁰

Does ashwagandha affect the kidneys?

Not in the trials that measured kidney function, all in healthy adults: in the 1,002-adult trial, creatinine, the blood marker of kidney function, stayed in the normal range on 600 mg a day for 8 weeks, with no significant difference from placebo.² Kidney markers stayed within normal ranges across the 23-trial review.¹ One case report points the other way: a 69-year-old man with a kidney transplant developed acute rejection two weeks after starting ashwagandha and later lost the transplanted kidney; his doctors found no other trigger and advise warning transplant recipients.¹¹ A PubMed search on 13 October 2026 (ashwagandha or Withania with kidney, renal, nephrotoxicity, creatinine or stones) found no report of kidney stones and no trial in people with kidney disease. The NHS says not to take herbal medicines with kidney problems, and with chronic kidney disease to check with a doctor or pharmacist before taking nutritional supplements.^{6, 12}

Can ashwagandha affect the thyroid or cortisol?

The thyroid, in one direction: across 23 pooled trials of 1,706 people, thyroxine (T4) rose by 0.61 µg/dL while TSH and T3 did not change.⁸ Three case reports describe an overactive thyroid: a 32-year-old Dutch woman after raising her dose, a 73-year-old American woman with a fast heart rhythm after two years of use, and a 47-year-old Japanese man two months in; all improved after stopping.^{13, 14, 15} The NHS lists palpitations, trembling, nervousness and difficulty sleeping among the symptoms of an overactive thyroid; a GP can arrange a blood test.¹⁶ Anyone with a thyroid condition or on thyroid medicine asks their GP first: ashwagandha with levothyroxine. Cortisol: one London case report describes a 37-year-old woman taking ashwagandha with very low cortisol and sodium, who recovered in hospital; it does not prove the cause.¹⁷

Can ashwagandha cause hair loss, constipation, headaches or weight gain?

Hair loss: a PubMed search on 13 October 2026 found no case report of it, and in one 75-day trial, extract supplied by its maker, hair density and growth measures improved more than on placebo.¹⁸ Constipation: not among the effects recorded in the largest trial or the 23-trial review, and a search the same day found no report of it as a side effect.^{1, 2} Headaches: recorded on placebo too, 0.2% against 2.2% in the largest trial; no trial has tested ashwagandha for migraine.² Weight gain: not among the recorded effects; in 66 postmenopausal women over 12 weeks, body fat changed by -0.6 percentage points against +0.03 on placebo.¹⁹

Is ashwagandha addictive, and what happens when you stop?

No study has tested dependence. One case report describes a 20-year-old man who developed a racing heart, insomnia and anxiety after abruptly stopping 600 mg a day; his heart, liver and thyroid tests were normal, and the authors allow that his underlying anxiety may have returned.²⁰ Breaks and how to stop: is ashwagandha safe to take daily.

When should you stop and see a GP?

Stop and seek help the same day for dark urine, pale stools, itching, or yellow skin or eyes. See a GP for new palpitations, tremor or breathlessness, and for low mood or a flat feeling that persists after stopping (what ashwagandha does for the brain); anyone on an antidepressant tells their prescriber first (ashwagandha with antidepressants). The NHS herbal-medicines page says not to take them with kidney or liver problems or certain medicines, and to check with a pharmacist first if you take other medicine.⁶ Fasting glucose fell slightly across 11 trials, at very low certainty, so anyone on diabetes medicine asks a pharmacist first.²¹ Every caution: who should not take ashwagandha. Report a suspected reaction to the MHRA Yellow Card scheme.²² No ashwagandha product holds a UK traditional herbal registration, and the Committee on Toxicity has yet to publish its statement.^{23, 24}

What we don't know

• No trial in the 23-trial review ran beyond 180 days.
• No study has measured how often the liver reaction happens or who is at risk of it.
• No trial has enrolled people with kidney disease or a kidney transplant.
• The 23-trial review covered only single-ingredient root extracts, so leaf extracts and blends sit outside it.

Frequently asked questions

What organ is ashwagandha hard on?

The liver, in the published cases above. Kidney, blood and heart markers stayed within normal ranges across the 23 safety trials, all in generally healthy adults.¹

Can I take ashwagandha with amlodipine?

No human interaction study exists (PubMed search, 13 October 2026). The NHS lists medicines for high blood pressure among those that may not mix well with herbal medicines, and a US drug reference advises caution in high blood pressure, so ask a pharmacist before the first dose.^{6, 7}

Why can't I sleep after taking ashwagandha?

The 23-trial review lists transient drowsiness, not insomnia, among its infrequent mild effects;¹ some users describe feeling wired, especially after a late dose. No trial has compared morning with evening doses; timing is in how to take ashwagandha. Sleeplessness with palpitations or trembling is a GP visit, since both are overactive-thyroid symptoms.¹⁶

Sources

1. Coope et al., 2026. Systematic review, 23 randomised trials, 2,317 healthy adults; two authors employed by UK supplement companies. PubMed 42198398.
2. Pakhale et al., 2026. Randomised trial, 1,002 adults with stress and anxiety, 8 weeks; industry-funded, extract supplied by its maker. PubMed 41943502.
3. McIntyre et al., 2026. Scoping review, 13 case publications, 25 patients. PubMed 42367407.
4. Verma et al., 2021. Randomised trial, 80 healthy adults, 8 weeks; funding not checked. PubMed 33338583.
5. Salve et al., 2026. Observational study, 191 adults, 12 months, no placebo group. PubMed 41063394.
6. NHS. Herbal medicines and complementary therapies. Page last reviewed 1 May 2026. nhs.uk.
7. Drugs and Lactation Database (LactMed). Withania. Reference entry, revised 15 December 2024. PubMed 30000965.
8. Fornalik et al., 2026. Pooled analysis, 23 randomised trials, 1,706 people. PubMed 41740946.
9. Philips et al., 2023. Case series, 8 patients. PubMed 37756041.
10. NHS. Jaundice. Page last reviewed 22 January 2024. nhs.uk.
11. Sriperumbuduri et al., 2020. Case report, 1 man with a kidney transplant. PubMed 33305135.
12. NHS. Chronic kidney disease: living with. Page last reviewed 22 March 2023 (review overdue). nhs.uk.
13. van der Hooft et al., 2005. Case report, 1 woman, in Dutch. PubMed 16355578.
14. Kamal et al., 2022. Case report, 1 woman. PubMed 35475098.
15. Hayashi et al., 2024. Case report, 1 man. PubMed 38559552.
16. NHS. Overactive thyroid (hyperthyroidism). Page last reviewed 11 April 2023 (review overdue). nhs.uk.
17. Patel et al., 2024. Case report, 1 woman. PubMed 38941978.
18. Jillella et al., 2026. Randomised trial, adults with hair loss or skin conditions, 75 days; size not stated in the abstract; extract supplied by its maker. PubMed 41770039.
19. Obhrai et al., 2026. Randomised trial, 66 postmenopausal women, 12 weeks; no conflicts reported. PubMed 42742071.
20. Holzman et al., 2025. Case report, 1 man. PubMed 40476122.
21. Farrin et al., 2026. Pooled analysis, 11 randomised trials, 667 people; very low certainty (GRADE). PubMed 42641800.
22. MHRA. The Yellow Card scheme: guidance. Last updated 24 July 2025. gov.uk.
23. MHRA. Herbal medicines granted a traditional herbal registration (THR); list dated 27 October 2025. gov.uk.
24. Committee on Toxicity. 8th September 2026 meeting; TOX/2026/30 on ashwagandha not yet available on 13 October 2026. gov.uk.

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