Quick answer

In trials lasting up to about 3 months, ashwagandha's side effects were usually mild: upset stomach, loose stools, nausea and drowsiness. The serious risks are rare: liver injury, usually 2 to 12 weeks after starting, and changes in thyroid hormone. NIH says to avoid it in pregnancy and while breastfeeding.^1,2,3

Key facts

In an 8-week trial of 1,002 adults, fewer side effects were recorded on ashwagandha than on placebo.⁴
NIH's LiverTox database rates ashwagandha a likely cause of rare liver injury.²
Three women developed an overactive thyroid while taking it, and it settled when they stopped.¹
Denmark banned ashwagandha in supplements in 2023.¹

Common, mild side effects

Common side effects are usually mild: upset stomach, loose stools, nausea and drowsiness. Vomiting has also been reported.^1,3,5

In an 8-week trial of 1,002 adults, 28 side effects were recorded among the 498 people taking 600 mg a day and 46 among the 504 taking placebo. The most common were nausea, dry mouth and headache, and liver and kidney blood tests did not change.⁴

A smaller 8-week safety trial gave 80 healthy adults, half of them women, 300 mg twice a day or placebo. Blood counts, liver and kidney tests and thyroid hormones did not change significantly, and no one reported an adverse event.⁶

Liver injury: rare but serious

Rare cases of liver injury have been linked to ashwagandha, usually starting 2 to 12 weeks after people began taking it, with jaundice and itching. Most resolved within 1 to 4 months of stopping, but a few were fatal or needed a liver transplant, mainly in people who already had liver disease.^1,2

In five reported cases of liver injury, people had taken 450 to 1,350 mg a day for 1 week to 4 months.¹

LiverTox calls these cases rare given how widely ashwagandha is used. In a series of 8 cases from three hospitals in India, the 3 people who died already had chronic liver disease. In another report, a 41-year-old woman needed an emergency liver transplant. In several cases the product was tested and contained ashwagandha with no contaminant found.²

Stop taking it and see a doctor if you notice yellow skin or eyes, itching, nausea, unusual tiredness or stomach discomfort. Do not start it again after a reaction like this.^1,2

Thyroid and other hormones

Ashwagandha may change thyroid hormone levels. In a trial of 50 people with a mildly underactive thyroid, 600 mg a day for 8 weeks lowered TSH and raised T3 and T4, and three women developed an overactive thyroid while taking it, which settled when they stopped.^1,7

In a smaller study, three men taking 500 mg a day of a root and leaf extract for 8 weeks had small rises in T4. A 2026 pooled analysis of 23 trials also found a modest rise in T4, without changes in TSH or T3.^1,8

Ask your pharmacist or doctor first

NIH says ashwagandha might interact with thyroid hormone medicines, such as levothyroxine. The concern comes from studies in which ashwagandha raised thyroid hormone levels, and from case reports of an overactive thyroid in people taking it.^1,3,5,9

Expected from how the two work, not shown in studies

Ashwagandha might raise testosterone levels, so experts say it might not be safe for men with hormone-sensitive prostate cancer.^1,3

Pregnancy, breastfeeding and the bans

NIH's complementary health center says ashwagandha should be avoided during pregnancy and not used while breastfeeding. Some reports suggested it could cause miscarriage, although the American Herbal Pharmacopoeia says its own report on the root has been misrepresented.^1,3

Denmark banned ashwagandha in supplements in 2023 after a risk assessment raised concerns about pregnancy and about thyroid and sex hormones. In 2024, France's food safety agency advised against its use by some groups, including pregnant and breastfeeding women and people with hormone conditions.¹

Medicines it might interact with

Ask your pharmacist or doctor first

NIH's complementary health center says there is evidence that ashwagandha might interact with medicines for high blood pressure, and NIH's dietary supplement office lists them too. Neither says how large the effect might be or which medicines are most affected.^1,3,5

Reported in studies

NIH's two fact sheets and its complementary health center also name diabetes medicines, sedatives, anti-seizure medicines and medicines that suppress the immune system. NIH's complementary health center does not recommend ashwagandha for people with autoimmune or thyroid disorders, or for anyone about to have surgery.^1,3,5

Who should not take it, or should ask first

Do not take it if you are pregnant or breastfeeding³
Do not take it if you have hormone-sensitive prostate cancer³
Ask your doctor first if you have liver disease, or have had jaundice or abnormal liver tests²
Ask first if you have a thyroid condition or an autoimmune condition, or take any of the medicines above³
Ask first if you have surgery planned, or are under 18^3,4

Questions people ask

Is ashwagandha safe?

For most adults in trials lasting up to about 3 months, side effects were mild and no more common than on placebo. Its safety over longer periods is unknown, it has rarely caused liver injury, and it is not for use in pregnancy, while breastfeeding, or with hormone-sensitive prostate cancer.^1,3,4

Is ashwagandha safe for teens?

It has not been studied in them. The trials cited here enrolled adults, for example people aged 18 to 65 in the largest safety trial. Ask a doctor before giving it to anyone under 18.⁴

Should I stop ashwagandha before surgery?

NIH's complementary health center says ashwagandha is not recommended for people who are about to have surgery. Tell your surgeon and anesthetist that you take it.³

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line Ashwagandha Complex

Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.