Ashwagandha side effects: who should avoid it and why

What are the common side effects of ashwagandha?

In clinical trials, which mostly lasted eight to twelve weeks, the side effects reported were usually mild and not much more frequent than with a placebo. The most common were:

• stomach upset, nausea, loose stools or diarrhoea
• drowsiness or feeling sluggish
• headache
• less often, dizziness or a skin rash

Trials are small and short, though, so they can miss rarer or slower-developing problems. Most of what we know about serious side effects comes from case reports and from the safety assessments carried out by food authorities.

What organ is ashwagandha hard on?

The organ that has raised most concern is the liver. The US National Institutes of Health’s LiverTox database describes a number of published cases of liver injury linked to ashwagandha supplements. These are rare and typically appear within a few weeks to a few months of starting. Most people recovered after stopping, but some cases were severe, and Germany’s Federal Institute for Risk Assessment notes reports that include acute liver failure.

People who already have liver disease, or who drink a lot of alcohol, should not take ashwagandha.

Why is ashwagandha bad for the thyroid?

Ashwagandha isn’t harmful to everyone’s thyroid, but it can affect thyroid hormone levels. A small trial in 50 adults with mildly underactive thyroids found that thyroid hormone levels changed significantly over eight weeks compared with placebo, and there are case reports of an overactive thyroid (thyrotoxicosis) in people taking ashwagandha. Germany’s Federal Institute for Risk Assessment lists effects on the thyroid among its concerns.

If you have an underactive or overactive thyroid, or take levothyroxine or other thyroid medicine, don’t start ashwagandha without speaking to your GP. Changing thyroid levels can affect how well your treatment is working.

Who should not take ashwagandha?

You should avoid ashwagandha, or speak to your GP or pharmacist first, if you:

• are pregnant, trying to get pregnant or breastfeeding – there isn’t enough safety data, and authorities advise against it;
• are under 18 – it hasn’t been properly studied in children;
• have liver disease or have had liver problems in the past;
• have a thyroid condition or take thyroid medicine;
• have an autoimmune condition such as rheumatoid arthritis, lupus, multiple sclerosis or type 1 diabetes – ashwagandha may affect the immune system;
• have had an organ transplant or take medicines that suppress the immune system;
• have a hormone-sensitive condition, including prostate cancer, because studies have reported changes in sex hormones;
• have surgery coming up.

Can you take ashwagandha while pregnant?

No. There’s not enough evidence that it’s safe in pregnancy, and in traditional use it has been linked with miscarriage. Germany’s Federal Institute for Risk Assessment and other European authorities specifically advise pregnant and breastfeeding women not to take ashwagandha supplements. If you’ve taken it before finding out you’re pregnant, stop and mention it to your midwife or GP.

What should you never mix with ashwagandha?

Ashwagandha may interact with several types of medicine. Speak to a pharmacist or GP before taking it if you use any of these:

Drinking alcohol at the same time may also add to drowsiness and to the strain on the liver. If you take any other herbal remedies, tell your pharmacist about those too.

Should you stop ashwagandha before surgery?

Yes, it’s sensible to. Because it may add to the effects of sedatives and may affect blood sugar and blood pressure, tell the team looking after you that you take it, and ask them how long before the operation you should stop.

Why shouldn’t you take ashwagandha daily for a long time?

It isn’t that daily use is known to be harmful – it’s that it hasn’t been studied well. Almost all trials lasted 12 weeks or less, and very few followed people for six months or more. That means there is little evidence either way on long-term safety.

If you do take it, stick to the dose on the label, review whether you still want to after a few months, and stop if you notice any of the warning signs above.

Why do I feel weird after taking ashwagandha?

Some people report feeling drowsy, “flat”, foggy or emotionally blunted, or having an upset stomach or vivid dreams. These reports are mostly anecdotal and not well studied, but if you feel unwell or just not yourself, stop taking it. If the feeling doesn’t go away, or you have any of the liver warning signs, contact your GP or NHS 111.

Is ashwagandha safe, and is it banned anywhere?

For most healthy adults in short trials it has been well tolerated, but European safety authorities say the data are too limited to set a safe intake level for supplements:

• United Kingdom: ashwagandha is legal in food supplements. The Food Standards Agency ran a call for evidence in 2024, and the independent Committee on Toxicity is carrying out a risk assessment. It discussed a second draft statement in May 2026; no final conclusion had been published by October 2026.
• Denmark: ashwagandha is not allowed in food supplements.
• Germany: the Federal Institute for Risk Assessment advises children, pregnant and breastfeeding women and people with liver disease not to take it, and other people to be cautious.

For background on what ashwagandha is and what has been studied, see What is ashwagandha?