Ashwagandha: interactions, thyroid, pregnancy
Futures Nutrition Editorial Team · 11 August 2026
Ashwagandha: interactions, thyroid, pregnancy
11 August 2026
The short answer: interactions between ashwagandha and medicines have been described — they just almost never appear on the pack. That is not because there are none, but because a food supplement is legally a food, and foods carry no patient information leaflet. Anyone taking medication for blood sugar, blood pressure or the thyroid, immunosuppressants, sedatives or antiepileptics is therefore better off clearing the matter with a doctor beforehand.
And for some groups, authorities do not advise a conversation but advise against it altogether: the German Federal Institute for Risk Assessment (BfR) recommends that "children, pregnant and breastfeeding women and people with an existing or previous liver disease in particular" do not take ashwagandha preparations (statement 039/2024).
Why none of this is printed on the tub
For a medicine, § 11 of the German Medicines Act requires side effects, interactions and contraindications to appear in the package leaflet. For foods there is no such duty. Section 4 of the German Food Supplements Ordinance prescribes only three sentences: do not exceed the stated daily dose, no substitute for a balanced diet, keep out of the reach of young children. Everything else — warnings for pregnant women, for people with liver disease, for anyone on long-term medication — is voluntary.
Just how voluntary was counted by the consumer association of North Rhine-Westphalia (Verbraucherzentrale Nordrhein-Westfalen) across 73 ashwagandha products from online and bricks-and-mortar retail (market survey report of 20 April 2026):
| Warning | Products carrying it | of 73 |
|---|---|---|
| any notice for any group of people | 48% | 35 |
| pregnant / breastfeeding women | 43.8% | 32 |
| children | 30% | 22 |
| people with liver disease | 15% | 11 |
| possible interactions with medicines | 11% | 8 |
So a reference to interactions was found on one product in ten. The combination of all the notices recommended by the BfR plus an interaction warning did not occur once in the entire survey. A high price did not help: in the premium segment only 54% carried any warning at all, fewer than the small packs at 75%.
From this follows the practical rule for buying: the absence of a list of interactions is not a statement about interactions. It is only the absence of an obligation.
Which drug groups are named
The following groups appear in assessments by authorities. None of them automatically means that something will happen — they mean that a coincidence is conceivable and therefore belongs in a conversation.
| Drug group | Why it is named | Source |
|---|---|---|
| antidiabetics | indications of effects on blood sugar levels; in diabetes the value could drop too far | BfR 039/2024 |
| antihypertensives | indications of effects on blood pressure | BfR 039/2024 |
| immunosuppressants | indications of an influence on the immune system | BfR 039/2024 |
| thyroid hormones (e.g. levothyroxine) | indications of effects on thyroid hormones | BfR 039/2024, HoA report 2024 |
| sedatives and sleep medication, antiepileptics | traditional reports of strengthened or weakened effect | WHO monograph 2009; Polish mandatory notice |
| cardiac glycosides (digoxin) | withaferin A is structurally similar to digoxin and can produce falsely high or falsely low levels in certain immunoassays | BfR 2013 |
| medicines metabolised via CYP2B6 and CYP3A4 | described interactions at the level of liver enzymes | MSKCC, as of 2024 |
The digoxin entry is the most interesting, because it concerns not the effect but the measurement: the laboratory value can come out wrong without anything having changed in the patient. Anyone taking cardiac glycosides and having their levels monitored should mention ashwagandha at the practice — otherwise a measurement artefact is mistaken for a finding.
The WHO monograph of 2009 states for the drug that it may strengthen the effect of barbiturates and weaken that of diazepam and clonazepam; the information there comes from the American Herbal Pharmacopoeia of 2000. Poland has turned this into a mandatory notice: products must warn against taking them together with sedatives, sleeping pills or antiepileptics.
The thyroid: why it appears in every list
The thyroid is the point at which several assessments meet independently of one another. As early as 2013 the BfR voiced safety concerns "arising from indications of an influence on thyroid function" and proposed adding the root to the scrutiny list in Annex III of Regulation (EC) No 1925/2006. In 2024 it put the point more generally: there are indications that the preparations "may influence the immune system as well as the endocrine system (effects on cortisol and blood sugar levels, thyroid and sex hormones)" — a risk statement, not a claim of benefit.
The first report of the "Food Supplements" working group of the Heads of Food Safety Agencies (HoA), an association of 30 European countries, published in 2024, lists 117 substances that should not be used in food supplements or only in a limited way because of their possible risk. Twelve of them are considered a priority for regulation, among them Withania somnifera. As the most critical endpoints the report names effects on male reproduction via the sex hormones, effects on thyroid hormones, inhibition of acetylcholinesterase, effects on the immune system and liver toxicity. A health-based guidance value — an amount below which a risk would not be expected — could not be derived so far.
Two national authorities explicitly single out the thyroid. Denmark banned ashwagandha in food supplements in April 2023, on the basis of a risk assessment by the Technical University of Denmark which in 2020 had raised concerns about hormonal disruption — including of the thyroid — and possible risks to reproduction. The French authority ANSES advised on 19 April 2024 that people with thyroid, liver or heart disease, among others, should not take it.
For everyday life this means: anyone stabilised on levothyroxine has a dose that was adjusted against laboratory values. A preparation with indications of effects on thyroid hormones belongs, in that case, in the conversation with the treating practice — before the first day, not after the next check-up.
Pregnancy, breastfeeding and trying to conceive
Here the data are not thin; the assessment is old and unanimous. The WHO monograph of 2009 lists pregnancy and breastfeeding as contraindications and justifies this with missing safety data and the traditional use of the drug to induce abortion. In 2024 the BfR named pregnant and breastfeeding women in the same group as children and people with liver disease. The Dutch RIVM presented a safety assessment in March 2024 and recommended that consumers not use plant preparations containing ashwagandha, especially not during pregnancy.
The consumer association points to the detail most easily overlooked: a pregnancy is typically noticed only after some weeks. Anyone who wishes to have a child and takes ashwagandha may therefore be covering precisely the early phase in which the pregnancy is still unknown. That is why the recommendation there is not "stop during pregnancy" but abstain while trying to conceive.
The 43.8% of products that carry any pregnancy notice at all mostly do so with the standard sentence "not suitable for pregnant and breastfeeding women" found on a great many food supplements. Here it is, for once, more than a manufacturer covering itself.
The liver: case reports, not statistics
The BfR names case reports of liver damage as grounds for particular caution. The Dutch pharmacovigilance centre Lareb, reported on by the German journal arznei-telegramm in 2025, is more specific: after a first warning in September 2023, a total of twelve reports of liver damage in connection with ashwagandha food supplements had been received there; in seven cases the suspected product contained ashwagandha only. Described were fatigue, weakness, nausea, loss of appetite, abdominal pain, itching as well as dark urine and jaundice — occurring between one week and several months after starting.
Twelve reports are not a frequency: it is not known how many people took the product without anything unusual, and a reporting system records suspected cases, not proven causes. What they are, though, is the reason why the liver is named separately in almost every European statement. Which other undesirable effects have been reported is covered in ashwagandha side effects.
What this means in practice
Three things can be decided before buying:
- Check what is declared. Plant part, extract, marker content in per cent and the resulting amount in milligrams per daily portion. For comparison: Poland permits a maximum of 3 g of root powder or a maximum of 10 mg of withanolides per daily portion; in Germany there is no such upper limit. How to read those figures is explained in KSM-66 or Sensoril.
- Go through your own medication list — including the things you do not think of as medication, such as the thyroid tablet in the morning.
- Do not leave the duration to chance. Why there is no official specification for it is explained in how long, and when to pause.
Our ashwagandha extract declares Withania somnifera, root, 10% withanolides, one tablet daily with a meal. Which plant part was processed is no minor matter — it is one of the four label details by which a declaration can be judged, described in what counts on the label.
With the combination with melatonin a second component is added, for which an authorised claim exists: "Melatonin contributes to the reduction of time taken to fall asleep." The beneficial effect is obtained with the consumption of 1 mg of melatonin close to bedtime. Anyone also taking a pure melatonin product should add the two amounts together rather than running them side by side. Both preparations stand next to each other in the ashwagandha category.
Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.
Common questions
I take levothyroxine. Is ashwagandha off limits?
There is no general ban in Germany — but the combination belongs in a conversation with a doctor. The BfR names indications of effects on thyroid hormones, and ANSES explicitly advises people with thyroid disease against it. Anyone who is stabilised has a dose adapted to laboratory values; an additional factor makes the monitoring harder to interpret.
There is no warning on my pack. Does that make the product safer?
No. The notice is voluntary, and its absence says nothing about the contents. The consumer association draws the opposite conclusion: do not buy a product that lacks the warning recommended by the BfR, because a missing notice does not speak for a careful manufacturer. Under Article 14 of Regulation (EC) No 178/2002, responsibility for safety lies with the manufacturer anyway, not with the authority.
Are there interactions with other food supplements?
For combinations of ashwagandha with individual nutrients there are no robust investigations. What is relevant in practice is rather double counting: anyone taking several products that contain the same substance ends up with a higher daily amount than intended — that applies to melatonin just as much as to ashwagandha itself.
Do I have to stop ashwagandha before an operation?
That question belongs in the pre-operative consultation, not in a guide. Tell the anaesthetic and surgical team what you are taking, even if it is "only" a food supplement. The decision is made there, with a view to the rest of your medication.
