Ashwagandha and the thyroid:
what the studies show, what the authorities say and when not to take it
If you take levothyroxine or have Hashimoto’s thyroiditis, the short answer is no, not on your own. Not because the plant is dangerous for everyone, but for exactly the reason half the Romanian internet recommends it to you: in the only controlled study on the thyroid, ashwagandha lowered TSH and raised T3 and T4. A plant that shifts the numbers your doctor has just balanced with a pill is not a help. It is an extra variable, in a calculation that does not include it.
The short answer:
it depends what kind of thyroid problem you have
The question “can I take ashwagandha if I have thyroid problems” does not have one answer, it has four. “Thyroid problems” covers situations that behave completely differently, and articles that lump them together are exactly why people end up making the wrong decision.
If you take levothyroxine, your dose was calculated from your blood tests and checked by repeating them. Anything you add on top of it that shows up in those same tests is a variable nobody included in the calculation.
If you have Hashimoto’s thyroiditis, you are in the category for which there is no clinical study at all. Neither for, nor against. Chapter 5 explains why that absence matters more than it seems.
If you have hyperthyroidism, meaning too much hormone, the idea of taking something that raised T3 and T4 in studies does not hold up even in the most optimistic reading.
And if there is nothing wrong with your thyroid, the question is still valid. The published cases of thyrotoxicosis are not in people with thyroid disease. They are in people who had nothing wrong with them.
Ashwagandha is not added on top of thyroid treatment without the doctor who set your dose. Not because it is banned, but because it moves exactly the test the adjustment is based on.
The levothyroxine dose is titrated on TSH. Ashwagandha lowered TSH in a controlled study, so it can change precisely the number the adjustment is based on. Clinical databases classify the combination as a moderate interaction, with the advice to tell your doctor. The practical risk is not the plant, it is a dose change made on a test result whose cause nobody knows.
There is no clinical study on ashwagandha in autoimmune thyroiditis. The only thyroid study was done in subclinical hypothyroidism and does not report antibody status, so it cannot be read as an answer for Hashimoto’s. The French agency ANSES advises against its use by people with endocrine disorders, as a precaution. Precaution is the right register when there are no data.
No nuance is needed here. If the gland is already producing too much hormone, the plant’s only measured effect on the thyroid goes in the same direction. There is no scenario in which that is what you want, and no study suggesting otherwise.
Here the risk is small, but it is not zero, and it is useful to know what it looks like. The four published cases of thyrotoxicosis or thyroiditis appeared in people with no known thyroid disease. In all of them, the symptoms went away after the supplement was stopped. The signs: unexplained weight loss, palpitations, tremor, heat intolerance, frequent bowel movements.
What the studies measured:
TSH down, T3 and T4 up
There is only one controlled study on ashwagandha and the thyroid, published in 2018 by Sharma, Basu and Singh. Fifty participants with subclinical hypothyroidism, double blind, placebo controlled, 600 mg of root extract a day, eight weeks. The results were statistically significant on all three tests: TSH fell, T3 and T4 rose.
| Test | Direction of change | Statistical significance |
|---|---|---|
| TSH | fell | p < 0.001 |
| T3 | rose | p = 0.0031 |
| T4 | rose | p = 0.0096 |
The authors’ conclusion, translated word for word: treatment with ashwagandha “may be beneficial for normalising thyroid indices in subclinical hypothyroid patients”. The verb they chose is “may”, and the population is strictly the one in the title.
On top of that comes an observation from the professional fact sheet of the US National Institutes of Health: three adult men who took 500 mg a day of a standardised root and leaf extract for eight weeks had small increases in T4.
What the 2018 study does not say is longer than what it does say. It says nothing about Hashimoto’s. Nothing about people already taking levothyroxine. Nothing about what happens after eight weeks. And nobody has repeated it, on any larger scale.
The direction is what matters here, not the size of the effect. A substance that can lower TSH and raise T4 is a substance that can do so when you do not want it to as well.
Levothyroxine:
why “regulates the thyroid” is a problem, not a promise
Levothyroxine is not dosed by how you feel. It is dosed by TSH. The doctor starts with an amount, repeats the test after six to eight weeks and adjusts until the number falls within range. From that point on, TSH is the measuring instrument for the whole treatment.
Now add on top of it a plant that, in the only controlled study there is, lowers TSH. If you do not tell anyone you are taking it, one of two things happens. Either the result comes out lower and the doctor reduces your dose, even though your thyroid has not changed. Or you stop taking the plant between two tests, TSH goes back up, and now the reduced dose is too low.
This note is specific to thyroid treatment. For hormonal contraception, where the question comes up just as often, the situation is different and we have written about it separately, in the article on ashwagandha and the contraceptive pill.
Clinical interaction databases classify the combination of ashwagandha with levothyroxine as a moderate interaction, with the wording “ashwagandha may alter the effects of levothyroxine” and the advice to tell your doctor. It is not a ban. It is a requirement for transparency.
If you have already started and are only now reading this: do not stop abruptly in a panic and do not change anything on your own. Tell the doctor who monitors your thyroid what you are taking and since when, before your next blood test. An unexplained TSH value leads to a dose change, and a dose change made for an unknown cause is riskier than the plant.
The published cases:
what happened and how long it lasted
The National Institutes of Health professional fact sheet describes three cases of thyrotoxicosis in women aged 32 to 73 who were taking ashwagandha extract. One of them at an unusually high dose, 1,950 mg a day, for more than two months. In all three, the symptoms went away after the supplement was stopped.
A fourth case, published in 2024, is the best documented. A 47-year-old man, healthy until then, had been taking ashwagandha for two months for insomnia. He arrived at hospital with night fevers, fatigue, diarrhoea and four kilos lost in two weeks.
| Test | His value | Normal range |
|---|---|---|
| FT3 | 6.1 pg/mL | 2.3 to 4.0 |
| FT4 | 2.8 ng/dL | 0.9 to 1.7 |
| TSH | 0.001 µIU/mL | 0.35 to 4.94 |
| Thyroglobulin | 464 ng/dL | below 46 |
His thyroid antibodies came back negative, as did those that confirm Graves’ disease, and the scan showed almost zero uptake. The diagnosis: silent thyroiditis, meaning a temporary destruction of the gland, releasing the hormone already stored in it. He stopped the supplement on day ten. By day fifty he was back to normal.
A case report does not tell you how often something happens. It tells you that it can happen, what it looks like and, in this case, that it resolves when you stop. All three are worth knowing.
Honest to the end: four published cases, against millions of people taking ashwagandha, means a rare event. Case reports cannot measure frequency, by their very nature. But if you are losing weight for no reason, have palpitations and cannot tolerate heat a few weeks after starting, you have a concrete reason to stop and ask for a TSH test.
Hashimoto’s:
the category that has no answer yet
Here we are going to be less useful than you would like, because we have nothing to work with. There is no clinical study on ashwagandha in people with Hashimoto’s thyroiditis. What circulates in its place are two lines of reasoning, and neither is evidence.
The first line of reasoning, the optimistic one: the 2018 study normalised thyroid indices, so it would help. The problem is that the study was done in subclinical hypothyroidism, and its abstract does not report whether the participants had antibodies or not. Hashimoto’s is not defined by the TSH number, but by the autoimmune process behind it. A study that did not measure the process cannot answer questions about it.
The second line of reasoning, the pessimistic one: ashwagandha shows immunomodulatory activity in laboratory work, and Hashimoto’s is a disease in which the immune system attacks the thyroid, so it would make things worse. It is a reasonable concern. It has not been demonstrated in humans. “Makes Hashimoto’s worse” is just as unsupported a claim as “helps with Hashimoto’s”.
What is documented, on the other hand, is the position of a competent authority. In its opinion of 19 April 2024, the French agency ANSES advises against the use of ashwagandha by people with endocrine disorders, along with pregnant and breastfeeding women. When there are no data, caution is not timidity. It is the only position that can be defended.
What European authorities decided:
Denmark, France, Poland
This is the part completely missing from the top five results in Romanian, and it is the easiest of all to check. Ashwagandha is not a plant with a settled status in the European Union. Three member states have taken separate measures in the last six years, and two of them explicitly mention thyroid hormones.
| Country | Year | Measure |
|---|---|---|
| Denmark | 2020, then 2023 | A risk assessment by the Technical University of Denmark in 2020, discussing possible effects on thyroid and sex hormones and a possible abortifacient effect. The ban in supplements followed in 2023. |
| Poland | 2020 | Resolution 7/2020 of the food supplements team: root powder below 3 g a day, a maximum of 10 mg of withanolides per recommended daily dose, plus a mandatory warning on the label. |
| France | 2024 | ANSES opinion of 19 April 2024: advises against use by pregnant women, breastfeeding women and people with endocrine disorders. |
| Sweden | after 2020 | Adopted the Danish assessment framework, with less strict enforcement. |
The Polish label warning is worth reading in full, because it is broader than the thyroid: the product should not be taken by people using sedative, hypnotic or antiepileptic medicines, and it is not to be given to children, pregnant women or breastfeeding women.
In Romania we did not find a published national limit for withanolides. If there is one and we have missed it, write to us and we will correct the article the same day.
The dose in the 2018 study on subclinical hypothyroidism and the dose in our gummies.
The Polish ceiling is not a European limit and does not apply in Romania. We use it as a benchmark because it is the only official figure for withanolides published by a member state, and without a benchmark nobody can tell whether the dose on the box is high or low.
Five things you read in Romanian:
checked against the sources
We read the top five results in Romanian for “ashwagandha and the thyroid”. Three of them say the plant “regulates” the thyroid. One says it has no side effects at the recommended doses. None of them mentions the Danish ban, the ANSES opinion or any case report. Here is what we found when we looked for the sources.
It has two problems, one biological and one legal. Biologically, the only measured effect goes in one direction: TSH down, T3 and T4 up. Nothing moves both ways depending on need. Legally, ashwagandha has no authorised health claim in the European Union, so this sentence is not allowed to appear in commercial communication, whether or not it is true.
The three percentages appear identically on several Romanian pages, including one that sells the product. The published abstract of the study reports the directions and the significance thresholds, not percentages. We could not read these figures in a primary source, so we do not use them and we do not repeat them. A percentage being copied often does not make it verified.
Clinical databases list the combination with levothyroxine as a moderate interaction. The mandatory warning on the Polish label adds sedative, hypnotic and antiepileptic medicines. The US professional fact sheet also adds antidiabetic, antihypertensive and immunosuppressive medicines. “Natural” is not a pharmacological category.
The sentence is on a Romanian page, directly above a buy button. The French agency ANSES analysed eight reports of adverse effects received since 2009, four of which were classified as probably linked to the supplement, including acute hepatitis and jaundice. A rare effect is not a non-existent effect.
It is the sentence you see most often on the shelf, and it is the exact opposite of what you have read above. Ashwagandha really does move thyroid values in some people, and that is a reason for caution if you already have a thyroid condition, not a selling point.
The rest of the safety list:
liver, pregnancy, children, medicines
The thyroid is the subject of this article, but it is not the only thing worth knowing beforehand, especially if you intend to take ashwagandha for months on end.
The liver. The US professional fact sheet describes cases of liver injury in people aged 21 to 62, at doses between 450 and 1,350 mg a day, taken for between one week and four months, with jaundice, itching, nausea and fatigue. Their condition improved after stopping the supplement. The same fact sheet honestly notes the limits of these reports: the composition of the products was not independently verified in every case, and some also contained other ingredients.
Pregnancy and breastfeeding. ANSES advises against use by pregnant and breastfeeding women. The US fact sheet explains where the caution comes from, and also how it has been disputed: some reports have suggested a potential to cause miscarriage, and the American Herbal Pharmacopoeia has publicly responded that its report was misrepresented and that there is no evidence that ashwagandha root causes miscarriage. Both things are true at the same time. When the situation looks like this, the reasonable answer is not to take it during pregnancy.
Children. The Polish warning explicitly excludes them. There are no safety data in children.
Duration. Clinical studies have generally lasted between six and twelve weeks. Safety beyond three months is not known. That does not mean it is dangerous after three months, it means nobody has measured it.
Ask your doctor first, not afterwards: if you are pregnant or breastfeeding, if you have any thyroid condition, if you take levothyroxine, sedatives, antiepileptics, antidiabetics, antihypertensives or immunosuppressants, if you have a liver condition, or if it is for a child. Ashwagandha is not a medicine and does not replace any of these.
What is in our gummies
with ashwagandha
Two gummies a day means 600 mg of root extract, standardised to 5% withanolides, that is, around 30 mg of withanolides a day. It is the same amount of extract as in the 2018 study we wrote about above, and it is the figure you can compare any other box on the shelf against.
Ashwagandha is a plant with a long history in Ayurvedic medicine and with clinical studies in humans. What we can guarantee is the plant side, the amount and the standardisation, printed on the label. The rest is down to you and your doctor.
The product in this articleAshwagandha, in gummies600 mg of root extract a day, standardised to 5% withanolides. The full composition is on the page.See the compositionIf you have a thyroid condition, the question “what dose should I take” comes after the question “am I allowed to”, and no article can answer the second one for you. If you are allowed to and are interested in the time of day, we have written separately about when to take ashwagandha and which dose makes sense. And if you take several supplements at once, their timetable is the second question worth asking.
Frequently asked questions:
what people ask us about ashwagandha and the thyroid
Not on your own, without the doctor who set your dose. The levothyroxine dose is calculated from your TSH and checked by repeating the test. Ashwagandha lowered TSH in a controlled study, so it can shift exactly the number the adjustment is based on. The practical risk is not the plant, it is a dose change made on a test result nobody can explain.
They say nothing, and that is the problem. There is no clinical study on ashwagandha in people with autoimmune thyroiditis, either for or against. The only controlled thyroid study was done in subclinical hypothyroidism, in 50 people, over eight weeks. The French agency ANSES advises against use by people with endocrine disorders, as a precautionary measure.
In the 2018 study of 50 participants with subclinical hypothyroidism, 600 mg of root extract a day for eight weeks lowered TSH and raised T3 and T4 compared with placebo. The professional fact sheet of the US National Institutes of Health also describes three men with small increases in T4 at 500 mg a day. A single small study is not a certainty, but the direction is consistent.
Rarely, and case reports cannot say how rarely. Three cases have been described in women aged 32 to 73, plus one case published in 2024 in a 47-year-old man. What they have in common matters more than the number: the symptoms disappeared after the supplement was stopped, in every case. The signs to watch for are unexplained weight loss, palpitations, tremor and heat intolerance.
On the basis of a 2020 risk assessment by the Technical University of Denmark, which discusses possible effects on thyroid and sex hormones and a possible abortifacient effect. The ban in food supplements followed in 2023. Sweden adopted the Danish assessment framework. In France, ANSES did not ban it, but advised against it for certain groups of people in its opinion of 19 April 2024.
Around 30 mg, if the extract is standardised to 5% withanolides, as the one in our gummies is. For comparison, in 2020 Poland set a ceiling of 10 mg of withanolides per recommended daily dose of a supplement. It is not a European limit and does not apply in Romania, but it is the only official figure for withanolides published by a member state.
Note: the information in this article is for educational purposes. It does not replace personalised medical advice. Ashwagandha has no authorised health claims in the European Union, and this article does not attribute any health effect to it. Food supplements are not medicines and are not intended to diagnose, treat or prevent disease. Do not exceed the recommended daily dose. Keep out of the reach of children.
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