Ashwagandha Side Effects and the Thyroid: When Caution Is Warranted
A plant bought to ease stress may quietly turn the dials on your thyroid. With Hashimoto's, on thyroid hormones or with a diseased liver, it is therefore not a harmless wellness product. No panic. But no playing it down either.
Plant-based does not mean harmless. It only means the active ingredient comes from a root rather than a lab. If you take a plant seriously, you also take its side effects seriously.
May I ask you an uncomfortable question? When did you last look up the side effects of a supplement before ordering it?
Most of us don't. With tablets from the pharmacy, we read the package leaflet. With capsules that have a leaf on the label, we read the promises. Calm. Sleep. Balance. Ashwagandha is the perfect example.
Maybe you have Hashimoto's. Maybe you have been taking levothyroxine for years. And maybe you read in a forum that ashwagandha is good for the thyroid. Then this text is for you. Not to frighten you. But so that you know where this plant may intervene in your body, and when it has no business being there.
If you first want to know what ashwagandha may do for stress and cortisol, read my core article on its effects. This one is about the other side of the coin.
What to expect here
- Why a stress plant can touch the thyroid
- What studies show on TSH, T3 and T4
- Case reports of overactive thyroid and thyroiditis
- Hashimoto's through the immune system lens
- Liver injury: how rare, how serious
- Interactions with medications
- Warning signs that mean you should stop
- Which values belong measured before and during use
Why a stress plant can touch the thyroid
Imagine your hormone system as a mixing desk. Many faders, one shared current. Whoever moves one fader often changes the sound of the others too. Ashwagandha is bought to turn the stress fader down. But the hand that moves it may brush against the thyroid fader.
The thyroid works in a feedback loop. The pituitary gland sends TSH, the control signal. The thyroid responds with T4, the storage form, and some T3, the active form. When T4 rises, TSH falls. When T4 falls, TSH rises. A thermostat that adjusts itself.
Hypothalamus and pituitary
The brain measures how much thyroid hormone is in the blood and sends out TSH as a signal when needed.
Thyroid
It mainly produces T4. In Hashimoto's, this very organ is the target of an autoimmune reaction.
Conversion in the tissues
T4 is converted into active T3 in the liver and other tissues. Only T3 turns up the metabolism of the cells.
Possible point of intervention
Studies suggest that ashwagandha may raise T4 and T3. The brain may respond with a lower TSH.
The first clue came from the animal lab.
In 1998, two researchers at the University of Indore gave male mice a high daily dose of ashwagandha root extract for 20 days. Afterwards, T3 and T4 in the blood were elevated, while conversion in the liver remained unchanged.
This is an animal study with a dose that cannot be transferred one to one to humans. But it shows where the question comes from: the plant appears to stimulate the thyroid itself.
Panda S, Kar A. J Pharm Pharmacol. 1998;50(9):1065-1068. DOI: 10.1111/j.2042-7158.1998.tb06923.xIn 2016, a team from Varanasi, India, gave people with subclinical hypothyroidism, meaning a mildly elevated TSH between 4.5 and 10, either 600 milligrams of ashwagandha root extract daily or placebo. After 8 weeks, TSH had dropped markedly in the ashwagandha group, and T3 and T4 had risen.
The authors interpret this as a possible benefit in mild hypothyroidism. For you, the other reading matters more: the plant can measurably turn the dials on your thyroid values. And a dial that can turn in one direction is not a neutral bystander.
Sharma AK et al. J Altern Complement Med. 2018;24(3):243-248. DOI: 10.1089/acm.2017.0183In 2014, psychiatrists at the University of Pittsburgh analyzed the thyroid values from an ashwagandha study in bipolar disorder. In all three ashwagandha participants with abnormal values, T4 rose by 7, 12 and 24 percent over 8 weeks, while under placebo it tended to fall in six of seven people.
The numbers are tiny, as the authors themselves stress. Their conclusion is clear nonetheless: vigilance for an overactive thyroid may be warranted.
Gannon JM et al. J Ayurveda Integr Med. 2014;5(4):241-245. DOI: 10.4103/0975-9476.146566For balance, the counterpoint belongs here too. A randomized safety study in 80 healthy adults found no notable change in the thyroid profile with 300 milligrams twice daily over 8 weeks. A 2023 systematic review of medicinal plants in hypothyroidism could find only four randomized trials in total, including a single one on ashwagandha. So the data are thin.
"Good for the thyroid" is the wrong question. The right one is: in which direction can the plant pull, and do I need that right now?
With an untreated mild hypothyroidism, an upward pull may seem harmless. With a stable dose of hormone therapy, with an overactive thyroid or in an inflammatory phase of Hashimoto's, the same pull may be too much.
And now you know why I never look at ashwagandha separately from your thyroid values.
When the dial turns too far: overactive thyroid and thyroiditis
Many people with a thyroid condition know this feeling. Suddenly your heart races at rest. Your hands tremble a little. Your sleep becomes thin even though you are exhausted. You blame it on stress. And perhaps reach for even more ashwagandha.
A patient with Hashimoto's and a TSH that shifted noticeably
A patient with Hashimoto's came in for a follow-up check. She felt more restless than usual and could not explain why.
In her lab results, her TSH had shifted noticeably compared with previous checks. Taking her history, it turned out that she had been taking ashwagandha during this period. After she stopped and with further checks, we kept an eye on her values together.
I cannot claim causality, but I document the temporal association. Hashimoto's values also fluctuate on their own.
The lesson: With a thyroid condition, every new product belongs in your medical history, including the herbal one from the drugstore.
Published case reports show that this is not only noticed in my practice.
In 2022, a clinic in Michigan described a 73-year-old woman who had taken ashwagandha on her own for two years against her underactive thyroid. She presented with supraventricular tachycardia, meaning episodes of a racing heart, signs of an overactive thyroid and a severely suppressed TSH.
After stopping, her symptoms and lab values returned fully to normal. For you, the case shows: precisely those who take the plant for their thyroid may overshoot the target.
Kamal HI et al. Cureus. 2022;14(3):e23494. DOI: 10.7759/cureus.23494In 2024, physicians from Fukui, Japan, reported on a previously healthy 47-year-old man. Two months after starting the supplement, he developed exhaustion, night fevers, weight loss and diarrhea, and the diagnosis was painless thyroiditis with an overactive thyroid.
After stopping, his symptoms and values improved. What stands out is the type of disorder: a lymphocytic, that is immune-mediated, inflammation of the thyroid. This leads us straight to the immune system lens.
Hayashi M et al. Cureus. 2024;16(3):e55352. DOI: 10.7759/cureus.55352A case report does not prove a cause. It shows an event that coincides in time and recedes after stopping. When such reports from different countries resemble each other and a plausible mechanism fits, a signal emerges. That is exactly the kind of signal we have here. No more, but also no less.
And now you know why a racing heart while taking ashwagandha is not a stress symptom to be answered with more ashwagandha.
Hashimoto's through the immune system lens
Hashimoto's is not a hormone disease that happens to brush against the immune system. It is an immune disease that hits the hormones. This reversal of perspective is at the core of KPNI, Clinical Psychoneuroimmunology. It looks at how the nervous system, immune system, metabolism and hormones talk to each other.
In Hashimoto's, immune cells mistake parts of your own thyroid for something foreign. Imagine a security company that takes its own office building for a burglar. The question then is not only how much hormone the building still produces. The question is also: what makes the security company even more nervous?
In 2009, a research group in Portland gave five healthy people an ashwagandha root extract with milk for 96 hours. Afterwards, more CD4 helper cells were detectable, and natural killer cells showed activation markers.
Five people, four days, no control group. That is a hint, not proof. But the direction fits what has traditionally been attributed to the plant: it might stimulate the immune system rather than calm it.
Mikolai J et al. J Altern Complement Med. 2009;15(4):423-430. DOI: 10.1089/acm.2008.0215In a healthy person, a stimulated immune system may be unproblematic. With an autoimmune disease, it is not a neutral event. Mechanistically plausible, but not studied in people with Hashimoto's: additional immune activation could rather fuel the inflammation of the thyroid. Controlled studies in Hashimoto's simply do not exist.
In 2026, a pharmaceutical research group from Punjab compiled preclinical and clinical data on possible side effects. They list digestive complaints, hypersensitivity reactions of the immune system, liver injury and hormonal disturbances up to thyrotoxicosis and suppression of the adrenal glands.
The authors call for standardized dosing, longer safety studies and better reporting systems. For you, this means: even plant research that views ashwagandha favorably in principle now explicitly takes these risks seriously.
Kumar A et al. Phytother Res. 2026;40(8):4913-4931. DOI: 10.1002/ptr.70158A finding from stress research fits this picture. In an Australian study of 60 stressed adults, ashwagandha lowered not only morning cortisol but also DHEA-S. An older study of 64 adults also saw markedly lower cortisol. Cortisol is also one of the body's own brakes on inflammation. Lowering it permanently might take away part of the immune system's brake. Whether this is clinically relevant in autoimmune diseases, nobody knows today.
With Hashimoto's, the question is not whether a plant "strengthens the immune system". An immune system that turns against you does not need strengthening. It needs orientation.
Levers with better data for this orientation are stable sleep, steady blood sugar, adequate vitamin D status and a measured selenium status. That is less spectacular than a root from India. But it targets the immune system itself.
And now you know why I am particularly cautious with immune-active plants in autoimmune diseases.
The liver: rare, but serious
Imagine you have been taking something herbal for a few weeks. Then your skin itches, without a rash. Your urine turns dark. Someone tells you your eyes look yellowish. Hardly anyone connects this with a capsule for stress.
The liver is your body's treatment plant. Almost everything you swallow passes through it. Some substances are first converted into reactive intermediates before being excreted. The 2026 review describes exactly this pathway via cytochrome P450 enzymes as a possible mechanism for liver injury from ashwagandha.
In 2020, hepatologists at Landspitali University Hospital in Reykjavik, together with the US Drug-Induced Liver Injury Network, described five cases. All developed jaundice with nausea, fatigue and itching after 2 to 12 weeks, and the itching lasted 5 to 20 weeks in some cases.
No one developed liver failure, and in four of the five, values recovered within 1 to 5 months after stopping. Chemical analysis found ashwagandha but no other toxic admixtures.
Björnsson HK et al. Liver Int. 2020;40(4):825-829. DOI: 10.1111/liv.14393A group led by hepatologist Cyriac Philips in Kerala analyzed 23 cases from 2019 to 2022 and in 2023 described exactly eight people who had taken only ashwagandha as a single ingredient. The products contained only natural plant compounds, no contamination.
Five of the eight had pre-existing chronic liver disease. Three of them developed acute-on-chronic liver failure and died. For you, this means very concretely: known liver disease is a clear reason to stay away from it.
Philips CA et al. Hepatol Commun. 2023;7(10):e0270. DOI: 10.1097/HC9.0000000000000270There is also a report from Germany. In 2023, a team from Heidelberg described acute liver injury with jaundice two weeks after starting the supplement, which receded within five months after stopping without specific treatment.
- yellowing of the skin or the whites of the eyes
- dark urine or conspicuously pale stools
- persistent itching without a skin rash
- new nausea, pressure in the upper right abdomen, unusual fatigue
- racing heart, tremor, sweating, unintended weight loss or diarrhea
Measured against millions of users, these events are rare. In the safety study of 80 healthy adults, there were no abnormal liver values and no adverse events over 8 weeks. Both are true at the same time. Most people notice nothing. Some individuals experience something serious, often with a delay. Because nobody knows in advance who belongs to that group, checking your liver values is worthwhile.
And now you know why itching and dark urine while taking a herbal product are never a reason to wait and see.
Interactions and who is better off avoiding it
Maybe you have been taking a medication for so long that you no longer even perceive it as a medication. The little tablet in the morning. But that is exactly the point where a new substance can cause trouble.
Little here is proven by controlled interaction studies. Quite a bit is mechanistically plausible and named in reviews. I deliberately separate the two so you can see where knowledge ends and caution begins.
Levothyroxine and thyroid medications
If ashwagandha can raise T4 and T3, a stable dose might suddenly act as too high. Conversely, with an overactive thyroid treated with antithyroid drugs, the plant may work against the treatment.
Only with lab monitoringImmunosuppressants and autoimmune diseases
Given the indications of immune activation, the plant might run counter to immunosuppressive therapy. This applies, for example, after transplants or in rheumatic diseases. Data on this are lacking.
CautionSedatives, sleeping pills, alcohol
In studies, ashwagandha showed calming and sleep-promoting effects. Together with benzodiazepines, sleeping pills or alcohol, these effects may add up. This matters for driving and night shifts.
Additive effects possibleMedications broken down by the liver
Many medications are metabolized by the same cytochrome P450 enzymes that play a role in breaking down ashwagandha. For blood sugar and blood pressure medications, reliable data are lacking. Everything belongs on one medication list.
Medication listPregnancy and breastfeeding
A systematic review from 2025 found no reliable primary source for the often cited abortifacient effect. At the same time, high-quality human data on fertility and development are lacking. Uncertainty is not an argument for trying it here.
Do not useLiver disease, surgery, nightshade allergy
With known liver disease or elevated liver values, I clearly advise against it. Before planned procedures, discuss stopping with your surgical team. Ashwagandha belongs to the nightshade family.
Better to avoidIn 2025, an international group of authors including experts from authorities and industry summarized how ashwagandha is regulated worldwide. In the EU, the plant is under increasing scrutiny, and most recently a procedure under Article 8 of Regulation (EC) No 1925/2006 was recommended.
Such a procedure could end in a ban in food supplements. For you, this means: a product on the shelf is no proof that its safety has been conclusively verified.
Brendler T et al. Phytother Res. 2025;40(8):4845-4857. DOI: 10.1002/ptr.70151A plant that could change nothing in the body would have no side effects either. That ashwagandha can have side effects is therefore not a scandal. It is evidence that it is biologically active.
Anyone taking an active substance deserves the same care as with a medication: indication, monitoring, time frame.
And now you know why "it's only herbal" is not an argument, but a blind spot.
If you still want to take ashwagandha
Perhaps, after everything you have read, you still have good reasons. Genuine chronic stress, causes clarified, no thyroid or liver disease. Then it is not about a ban, but about safe supervision. Here is how I think about it.
Measure before starting
- TSH, free T3 and free T4
- TPO antibodies, and Tg antibodies if suspected
- Liver values: ALT, AST, GGT, alkaline phosphatase, bilirubin
- Current medication list, including supplements
While taking it
- Thyroid values again after a few weeks, especially on levothyroxine
- Liver values immediately with any warning sign, otherwise over the course
- Observe your own pulse and sleep
- A clear time frame instead of continuous use
Three levers for this week
- Inventory: Write down everything you take regularly, including powders, teas and capsules. Bring this list to every doctor's appointment.
- Conversation: If you have Hashimoto's or take thyroid hormones and use ashwagandha, deliberately raise this at your next TSH check.
- Take body signals seriously: A racing heart, dark urine or itching are not stress. They are a reason to stop and get checked.
"The best question before any product is not: What can it do? But: What harm can it do in my body, and how would I notice?"
Shukri Jarmoukli, ViveCura BerlinThis is not about a capsule. It is about trusting your body again because you understand it. If you know your values, you decide freely. If you don't, you decide in a fog.
Frequently asked questions about ashwagandha side effects
What side effects can ashwagandha have?
Controlled studies lasting 8 to 12 weeks mostly observed only mild complaints, such as digestive upset, tiredness or headaches, often about as frequently as with placebo. Rarer but more serious are changes in thyroid levels up to an overactive thyroid, liver injury with jaundice and possible effects on the immune system. A critical review from 2026 also lists hypersensitivity reactions and interactions with medications. These rare events barely show up in short studies because they are too uncommon to become visible there.
Can ashwagandha change thyroid levels?
There are indications that it can. In a small randomized trial in 50 people with subclinical hypothyroidism, 600 milligrams of root extract daily over 8 weeks was followed by a fall in TSH while T3 and T4 rose. In a study of people with bipolar disorder, T4 rose under ashwagandha in all three participants with abnormal values. An animal study in mice also showed higher thyroid hormones. A safety study in 80 healthy adults, on the other hand, found no notable changes. So the plant may influence the axis, but not in the same way in every person.
Can I take ashwagandha if I have Hashimoto's?
With Hashimoto's, I advise great restraint and only medically supervised use. There are two reasons. First, ashwagandha may shift thyroid levels, which could throw off a stable dose of hormone therapy. Second, immune-activating effects are attributed to the plant, and with an autoimmune disease that is not a neutral event. Controlled studies specifically in Hashimoto's are lacking. Where data are lacking, caution is the more honest answer.
Can ashwagandha trigger an overactive thyroid?
There are several case reports. In 2022, a 73-year-old woman was described who had taken ashwagandha on her own for two years against an underactive thyroid and came to hospital with a racing heart and signs of an overactive thyroid. In 2024, a Japanese clinic described a previously healthy 47-year-old man with painless thyroiditis after two months of ashwagandha. In both cases, symptoms and values receded after stopping. Case reports do not prove a cause, but they show a pattern worth knowing about.
Can ashwagandha be combined with levothyroxine?
Only with medical supervision and lab monitoring. There are no controlled interaction studies between ashwagandha and levothyroxine. Because the plant was able to raise thyroid hormones in studies, a shift towards overdosing is biologically plausible. If you take both, this belongs on your medication list, and TSH together with free T3 and T4 should be checked a few weeks after starting.
How common is liver injury from ashwagandha?
Rare, given how widely it is used, but well documented. In 2020, a case series from Iceland and the US Drug-Induced Liver Injury Network described five cases of jaundice after 2 to 12 weeks, which recovered within 1 to 5 months after stopping. In 2023, a series from India described eight cases with single-ingredient products without contamination. Three people with pre-existing liver disease died. An exact frequency cannot be derived from case series.
Which warning signs should make me stop?
For the liver: yellowing of the skin or eyes, dark urine, pale stools, persistent itching, new nausea or marked fatigue. For the thyroid: racing or skipping heartbeat, inner restlessness, tremor, sweating, unintended weight loss, diarrhea or sleeplessness. In both cases: stop taking it and have it checked by a doctor promptly, including liver and thyroid values.
Can you take ashwagandha during pregnancy?
No, I advise against it. A systematic review from 2025 found no reliable primary source for the historically reported abortifacient effect, and animal studies showed no reproductive toxicity at relevant doses. At the same time, the authors themselves stress that high-quality studies on fertility and development are lacking. During pregnancy and breastfeeding, uncertainty is not an argument for trying it.
Which medications can ashwagandha interact with?
Controlled interaction studies are scarce. From its profile of effects, however, there are areas where caution makes sense: thyroid hormones, immunosuppressants, sedatives and sleeping pills, and alcohol. A critical review also describes breakdown via cytochrome P450 enzymes, which metabolize many medications. For blood sugar and blood pressure medications, reliable data are lacking. Every new substance therefore belongs on your medication list.
Is ashwagandha banned in the EU?
As of the literature cited here, ashwagandha is not banned EU-wide. A regulatory review from 2025, however, describes that the plant is being scrutinized increasingly critically in the EU and that a procedure under Article 8 of Regulation (EC) No 1925/2006 has been recommended. Such a procedure could end in a restriction or a ban in food supplements. So a product on the shelf is not proof that its safety has been verified.
Further reading in the ViveCura guide
These articles connect directly to this topic.
Medicinal plants
Phytotherapy with evidence and limits
You are hereAshwagandha effects
What winter cherry may do and for whom
Adaptogens
What the term means and what it does not
Milk thistle
Liver protection between myth and data
Liver
How the liver works, beyond detox cures
Valerian and passionflower
Herbal calm for sleep
Saffron
Mood and the state of the evidence
Medicinal plants and the gut
How herbs may influence the microbiome
Hormones
Thyroid, cortisol, sex hormones
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