Does ashwagandha affect the thyroid? Yes, it can. A small placebo-controlled trial found that ashwagandha root extract raised thyroid hormone levels in people with a mildly underactive thyroid. Animal studies show the same direction of effect, and there are case reports of an overactive thyroid developing in healthy people who took it. That means ashwagandha isn't a neutral supplement for anyone with a thyroid condition. Here's what the evidence shows, who should be careful, and how to take it safely if you go ahead.
Ashwagandha can raise thyroid hormones. In an 8-week trial of 50 adults with subclinical hypothyroidism, 600 mg of root extract a day lowered TSH and raised T3 and T4 compared with placebo (Sharma 2018). In a trial in bipolar disorder, all three people on ashwagandha with abnormal thyroid tests had rising T4 (Gannon 2014). Two case reports describe thyrotoxicosis, an excess of thyroid hormone, after ashwagandha, which resolved when it was stopped (van der Hooft 2005; Hayashi 2024). Avoid it if you have an overactive thyroid. If you take levothyroxine, talk to your doctor first and have your thyroid tests rechecked after starting.
This article is general information, not medical advice. Don't change thyroid medicine without speaking to your doctor.
How Does the Thyroid Work?
The thyroid gland in your neck makes two main hormones, T4 (thyroxine) and T3 (triiodothyronine). They set the pace of your metabolism. The pituitary gland in the brain controls the thyroid by releasing TSH, thyroid-stimulating hormone.
When thyroid hormone levels are low, TSH rises to push the thyroid harder. When they're high, TSH falls. So a high TSH usually means an underactive thyroid (hypothyroidism), and a low TSH usually means an overactive one (hyperthyroidism). Subclinical hypothyroidism means TSH is raised but T4 is still normal, often with few or no symptoms.
What Did the Human Trial Find?
The main trial was done in India in 2016. Fifty adults aged 18 to 50 with a TSH between 4.5 and 10 were randomly assigned to 600 mg of ashwagandha root extract a day or a starch placebo for 8 weeks. Four people dropped out early (Sharma 2018).
Compared with placebo, the ashwagandha group had significantly lower TSH and higher T3 and T4 levels. The authors described thyroid tests as normalising over the 8 weeks. Side effects were few and mild: one person in the ashwagandha group and three in the placebo group reported any.
That sounds helpful for a mildly underactive thyroid, and it may be. But it was a small, single-centre pilot trial lasting two months. It didn't measure symptoms such as tiredness or weight, and it didn't follow people afterwards. It isn't enough to use ashwagandha as a treatment for hypothyroidism.
What Other Evidence Is There?
The bipolar disorder trial. In a US trial testing ashwagandha for thinking skills in bipolar disorder, thyroid tests were checked for safety. Of 60 participants, ten had an abnormal thyroid result. All three of those taking ashwagandha had T4 increases of 7%, 12% and 24%, and one person's mildly high TSH returned to normal. Six of the seven on placebo had falling T4. The authors cautioned that the numbers were small but advised vigilance about an overactive thyroid (Gannon 2014).
Animal studies. In adult male mice, ashwagandha root extract given daily for 20 days increased both T3 and T4 levels (Panda 1998). Other animal work points in the same direction.
Case reports. In the Netherlands, a healthy 32-year-old woman taking ashwagandha capsules for chronic fatigue developed thyrotoxicosis after increasing her dose. It resolved after she stopped, and her tests returned to normal (van der Hooft 2005). In Japan, a healthy 47-year-old man developed painless thyroiditis with thyrotoxicosis two months after starting ashwagandha, with fatigue, night fevers, weight loss and diarrhoea. He also recovered after stopping (Hayashi 2024).
Who Should Avoid Ashwagandha?
Based on the evidence, avoid ashwagandha if you have:
- Hyperthyroidism or Graves' disease. Raising thyroid hormones further could worsen symptoms such as a racing heart, anxiety, weight loss and tremor.
- A history of thyroiditis. One case report describes thyroiditis triggered after ashwagandha use.
- Pregnancy or breastfeeding. Ashwagandha isn't recommended in pregnancy, and thyroid balance is especially important then.
- Liver disease. Ashwagandha has been linked to rare liver injury. Our guide to ashwagandha side effects and liver safety covers the case reports.
Can You Take Ashwagandha With Levothyroxine?
Only with your doctor's agreement and monitoring. There's no study of ashwagandha in people taking levothyroxine. But if ashwagandha raises your own thyroid hormone output, your usual dose could become too much. Signs of too much thyroid hormone include palpitations, feeling hot, shakiness, anxiety, poor sleep and weight loss.
If you and your doctor decide to try it, a sensible approach is to have your thyroid tests rechecked about six to eight weeks after starting, the same interval often used after a levothyroxine dose change. Don't adjust your thyroid medicine yourself.
Timing matters too. Levothyroxine is sensitive to anything taken with it. Take it as prescribed, usually on an empty stomach, and take supplements several hours apart. Our article on mushrooms and thyroid health explains timing rules and which supplements can interfere with thyroid blood tests.
What About Hashimoto's Thyroiditis?
Hashimoto's is an autoimmune condition and the most common cause of an underactive thyroid. There are no trials of ashwagandha in Hashimoto's. Some people take it hoping to support their thyroid, but two uncertainties apply.
First, most people with Hashimoto's take levothyroxine, so the caution above applies. Second, ashwagandha seems to affect the immune system, and how that plays out in autoimmune disease isn't known. Our guide to mushrooms and autoimmune conditions explains why "immune-boosting" is a risky idea in autoimmunity. Talk to your endocrinologist before starting.
Should You Use Ashwagandha for a Sluggish Thyroid?
Not instead of a diagnosis. Tiredness, weight gain and feeling cold have many causes. A simple blood test can tell you whether your thyroid is involved. If you have subclinical hypothyroidism, your doctor may suggest monitoring rather than treatment, depending on your TSH level, symptoms and plans for pregnancy.
The 2018 trial is interesting, but it's one small study. If you want to try ashwagandha with a mildly raised TSH, do it with your doctor's knowledge and a follow-up blood test, so you can see what it's actually doing.
How Much Ashwagandha Was Used?
The thyroid trial used 600 mg of root extract a day. That's within the usual range of 300 to 600 mg a day used in stress and sleep trials. Our ashwagandha dosage guide explains how different extracts compare.
In the Dutch case report, symptoms appeared after the woman increased her dose. More isn't better here, and it's sensible to stay within studied amounts.
What Symptoms Should Make You Stop?
Stop ashwagandha and see a doctor if you notice:
- a racing or irregular heartbeat
- new anxiety, restlessness or shakiness
- unexplained weight loss or increased appetite
- feeling hot, sweating more or heat intolerance
- diarrhoea or more frequent bowel movements
- yellowing skin or eyes, dark urine or itching, which suggest a liver problem
In both case reports, symptoms resolved after stopping ashwagandha. Tell your doctor you've been taking it, because it may help explain abnormal test results.
What About Blends That Contain Ashwagandha?
Many "adaptogen", sleep, stress and testosterone blends include ashwagandha, sometimes without making it obvious. Check the full ingredient list if you have a thyroid condition. Some blends also add iodine-rich seaweed, which can affect the thyroid too. Our ashwagandha capsules contain a single root extract, so you know exactly what you're taking.
Frequently Asked Questions
Can ashwagandha cause hyperthyroidism?
Rarely, it appears it can. Two case reports describe thyrotoxicosis in previously healthy people after taking ashwagandha, which resolved when they stopped. Trials also show it raises thyroid hormone levels.
Is ashwagandha good for hypothyroidism?
One small 8-week trial found it improved thyroid test results in people with mild, subclinical hypothyroidism. That's not enough to recommend it as a treatment, and it hasn't been tested in people taking levothyroxine.
Can I take ashwagandha if I have Hashimoto's?
Ask your endocrinologist first. There are no trials in Hashimoto's, most patients take levothyroxine, and ashwagandha's immune effects in autoimmune disease aren't understood.
How long does ashwagandha take to affect thyroid levels?
In the trial, changes were measurable within 8 weeks. In one case report, thyroiditis appeared about two months after starting. If you take thyroid medicine, recheck your tests six to eight weeks after starting.
Should I stop ashwagandha before a thyroid blood test?
Don't stop it just for the test, but tell your doctor you take it, since it can genuinely change your thyroid hormone levels.
Related Articles
- Mushrooms and Thyroid Health
- Ashwagandha Side Effects and Liver Safety
- Ashwagandha for Women
- Ashwagandha Dosage Guide
- Sea Moss: Thyroid Support Guide
Sources
- Sharma AK, Basu I, Singh S. Efficacy and safety of ashwagandha root extract in subclinical hypothyroid patients: a double-blind, randomized placebo-controlled trial. J Altern Complement Med. 2018;24(3):243-248. PubMed 28829155
- Gannon JM, Forrest PE, Roy Chengappa KN. Subtle changes in thyroid indices during a placebo-controlled study of an extract of Withania somnifera in persons with bipolar disorder. J Ayurveda Integr Med. 2014;5(4):241-245. PubMed 25624699
- Panda S, Kar A. Changes in thyroid hormone concentrations after administration of ashwagandha root extract to adult male mice. J Pharm Pharmacol. 1998;50(9):1065-1068. PubMed 9811169
- van der Hooft CS, Hoekstra A, Winter A, de Smet PA, Stricker BH. Thyrotoxicosis following the use of ashwagandha. Ned Tijdschr Geneeskd. 2005;149(47):2637-2638. PubMed 16355578
- Hayashi M, Hamada H, Azuma SI, Hayashi K. Painless thyroiditis by Withania somnifera (ashwagandha). Cureus. 2024;16(3):e55352. PubMed 38559552