Supplements and safety
Ashwagandha Side Effects: What to Know, and What to Check
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed July 20266 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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Most people tolerate ashwagandha well. The common side effects are drowsiness, stomach upset and headache. Rarer but more serious risks are liver injury and an overactive thyroid. Some effects, like feeling wired or unusually flat, can reflect a shift in your thyroid or cortisol, both measurable in a blood test.
Feeling off since you started? Build your test →As of July 2026.Ashwagandha is one of the UK’s top-selling calming supplements. Most articles focus on whether it works. Fewer explain what can go wrong. This guide covers the reported side effects, plus a fresh reason for care: the US National Institutes of Health now rates ashwagandha a likely cause of rare liver injury.
Here is the short version. For most people, side effects are mild and settle. A small number see real problems, and two of them, thyroid and liver, are worth knowing about.
1. What are the common side effects?
Most reported side effects are mild. The ones people notice first are drowsiness, an upset stomach and headache. Larger doses make them more likely.
- Drowsiness. Ashwagandha is calming, so it can make you sleepy. Many people take it at night for that reason.
- Stomach upset. Nausea, loose stools or cramps can happen, especially on an empty stomach.
- Headache. Reported by some users, usually early on.
These effects tend to ease or stop when you lower the dose or take a break. The two risks below are rarer, but they matter more.
2. Can it affect your thyroid?
Yes. Ashwagandha can nudge your thyroid hormones up. Your thyroid is the gland in your neck that sets your metabolism. It runs on two signals: TSH (the message from your brain) and thyroid hormones like Free T4 (the output).
For most people that nudge is small and harmless. But if your thyroid is already overactive, or you take thyroid medication, it can push you into thyrotoxicosis, which simply means too much thyroid hormone in the blood. A 2022 case report describes exactly this in a person taking ashwagandha.
The signs overlap with stress: a racing heart, feeling wired, weight loss, shakiness or trouble sleeping. You cannot feel the difference between an anxious week and a busy thyroid. A blood test can. Our thyroid blood test guide explains what TSH and Free T4 show.
3. What about your liver?
This is the newest concern, and the reason care is worth it. As the supplement has boomed, so have reports of liver injury linked to it. The NIH LiverTox database, the official US record of drug and supplement liver harm, now puts it plainly:
“Cases of clinically apparent liver injury have been reported in patients taking commercial herbal products that are labelled as containing ashwagandha.”
— NIH LiverTox, Ashwagandha
It stays rare. But when it happens, it tends to show up 2 to 12 weeks after starting. Warning signs are yellow skin or eyes (jaundice), dark urine, itching and lasting nausea. Most people recover once they stop and get medical care.
This is a see-your-GP matter, not a home-test one. If you notice those signs, stop the supplement and speak to a clinician. Anyone with existing liver disease should avoid ashwagandha altogether.
4. Who should be most careful?
Ashwagandha is not for everyone. Take extra care, or avoid it, if you:
- Are pregnant or breastfeeding. It is not recommended in either case.
- Have a thyroid condition or take thyroid medication. It can add to your hormone load.
- Have liver disease or take other medicines that affect the liver.
- Have an autoimmune condition. Ashwagandha may stimulate the immune system.
- Are due surgery soon. Its sedative effect can add to anaesthetic.
If any of these apply, check with a pharmacist or GP before you start. It is a five-minute conversation that removes most of the risk.
5. How do you tell a side effect from something else?
This is the hard part. New tiredness, a low mood or a racing heart could be the supplement. Or they could be something the supplement is hiding. The same symptoms can come from a busy thyroid, high or low cortisol, low iron or low vitamin D.
You cannot feel which one it is. A blood test is the only way to tell them apart. A full blood count and a broader panel rule the common causes in or out.
Helvy’s General Energy & Wellness panel (£149, 17 markers) measures cortisol and thyroid (TSH and Free T4) alongside vitamin D and B12, the usual suspects behind the same symptoms. It is a home finger-prick test, with results in about five working days from UKAS-accredited UK laboratories.
A baseline before you start, and a retest after eight weeks, turns “I think it is doing something” into a number you can read. If low energy is the real issue, our tired-all-the-time guide walks through every testable cause.
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Helvy’s home blood tests report cortisol, thyroid, vitamin D and B12 with clear, plain-English context, so you can tell a side effect from a fixable cause. Results in about 5 working days from UKAS-accredited UK laboratories.
Frequently asked questions
Is ashwagandha safe?
For most healthy adults, short-term use is well tolerated. The common side effects are mild: drowsiness, stomach upset and headache. Rarer risks are thyroid overactivity and liver injury. Stay within trial doses, take breaks, and check with a pharmacist if you take other medicines. This is general information, not medical advice.
Can ashwagandha cause liver damage?
It is rare, but reported. The NIH LiverTox database rates ashwagandha a likely cause of clinically apparent liver injury. It usually appears 2 to 12 weeks after starting, with jaundice, dark urine and itching. Stop and see a clinician if you notice these. Avoid it entirely if you have liver disease.
Does ashwagandha affect the thyroid?
It can raise thyroid hormone levels. For most people the effect is small. But if your thyroid is already overactive, or you take thyroid medication, it can tip into thyrotoxicosis (too much thyroid hormone). A blood test of TSH and Free T4 shows where you sit, and a very abnormal result should be reviewed by a GP.
Who should not take ashwagandha?
Avoid it if you are pregnant or breastfeeding, or if you have liver disease. Take care if you have a thyroid or autoimmune condition, take sedatives or thyroid medicine, or have surgery coming up. When in doubt, ask a pharmacist first.