Can Ashwagandha Affect Thyroid Function?

Ashwagandha does affect thyroid function, and the effect is well enough documented that people with thyroid conditions should treat the supplement with real caution. A placebo-controlled trial in people with mildly underactive thyroids found that eight weeks of ashwagandha root extract significantly raised levels of the key thyroid hormones T3 and T4 while bringing down TSH. But the same thyroid-stimulating property that looks helpful for some has pushed others into thyrotoxicosis, a dangerous state of excess thyroid hormone output.

What the Trial Evidence Shows

The most cited clinical study on ashwagandha and the thyroid is a double-blind, randomized, placebo-controlled trial in 50 adults with subclinical hypothyroidism, a condition where TSH is elevated but thyroid hormones haven’t dropped enough to cause obvious symptoms. Participants took 600 mg of ashwagandha root extract daily for eight weeks. By the end of the trial, the ashwagandha group showed statistically significant improvements in TSH, T3, and T4 compared to placebo.¹

A systematic review of randomized trials in hypothyroidism put more specific numbers on the changes. In the ashwagandha arm, T3 levels climbed by about 19% at four weeks and roughly 42% by eight weeks. T4 rose by about 9% and 20% over the same intervals, while TSH fell significantly at both time points.² For someone whose thyroid is sluggish, a 42% increase in T3 over two months is not a subtle nudge. It’s a meaningful change in hormone output.

The trial was small, though, and eight weeks is a short window. An endocrinology review noted that while ashwagandha does appear to increase thyroid hormone production in both animal models and some human subjects, strong evidence supporting its use for long-term management of hypothyroidism doesn’t yet exist.³ The short-term effects are real, but whether they translate into lasting benefit is genuinely unresolved.

How Ashwagandha Appears to Work on the Thyroid

The earliest evidence came from animal studies. When researchers gave ashwagandha root extract to mice daily for 20 days, both T3 and T4 concentrations in the blood increased. The extract also boosted antioxidant enzyme activity in the liver and reduced a form of oxidative damage called lipid peroxidation. That combination suggested ashwagandha was stimulating the thyroid gland itself while also protecting surrounding tissue from stress.⁴

The mechanism doesn’t seem to involve ashwagandha binding directly to thyroid receptors the way a drug would. A recent evaluation of ashwagandha’s hormonal activities concluded that its effects on thyroid and other hormones likely result from modulation of central regulatory pathways rather than direct receptor binding.⁵ In practical terms, this means ashwagandha probably influences the brain’s signaling to the thyroid, specifically the hypothalamic-pituitary-thyroid axis, rather than acting on the gland directly.

This matters because a central-pathway mechanism can affect multiple hormone systems at once, which helps explain why ashwagandha also influences cortisol, testosterone, and other hormones. The thyroid effects aren’t isolated. They’re part of a broader shift in how the body regulates its endocrine system.

When the Effect Goes Too Far

The same property that makes ashwagandha interesting for hypothyroidism makes it potentially dangerous when it overshoots. Several case reports describe people developing thyrotoxicosis, an excess of thyroid hormones that causes symptoms like rapid heart rate, tremors, weight loss, and anxiety, after taking ashwagandha supplements.

One well-documented case involved a 73-year-old woman who had been using ashwagandha root extract on her own to manage hypothyroidism. After two years of supplementation, she presented with supraventricular tachycardia and significantly low TSH levels, both hallmarks of hyperthyroidism. Once she stopped taking the supplement, her symptoms resolved and her thyroid labs improved.⁶

As of a 2024 review, at least three case reports of ashwagandha-related thyrotoxicosis had been published. Two of those occurred in people who had previously normal thyroid function, and one was in a patient with pre-existing hypothyroidism.⁷ Three cases may sound trivial, but supplement side effects are massively underreported. Most people who experience thyroid changes on ashwagandha never connect the supplement to the problem, and even fewer end up as published case reports.

A critical review of ashwagandha’s adverse effects confirmed that its endocrine-modulating activity has been implicated in both thyrotoxicosis and adrenal suppression, underscoring the narrow margin between its therapeutic and toxic effects.⁸

People With Normal Thyroid Function

If you have a healthy thyroid and you’re taking ashwagandha for stress or sleep, should you worry? The evidence here is thinner but somewhat reassuring, with caveats.

A prospective observational study followed healthy adults taking a standardized ashwagandha root extract for 12 months, measuring clinical adverse events along with bloodwork for cortisol, liver function, kidney function, and thyroid function.⁹ The study was designed as a broad safety assessment, not specifically to test thyroid effects, but the inclusion of thyroid panels among the lab work suggests researchers are aware of the concern.

Still, two of the three reported thyrotoxicosis cases occurred in people who were previously healthy.⁷ A normal thyroid doesn’t guarantee immunity from ashwagandha’s stimulating effects, especially at higher doses or with prolonged use. The risk appears low in healthy people, but it exists. If you’re taking ashwagandha regularly and you start noticing symptoms like unexplained weight loss, a racing heartbeat, feeling unusually warm, or new anxiety, it’s worth getting your thyroid checked and telling your doctor about the supplement.

Who Should Be Especially Careful

Several groups face higher risk from ashwagandha’s thyroid effects:

People with thyroid disorders: Whether you have hypothyroidism, hyperthyroidism, or Hashimoto’s thyroiditis, ashwagandha can complicate your condition. For those already on thyroid medication, adding ashwagandha could push hormone levels out of the range your prescription is calibrated for.
Pregnant women: Safety evaluations have flagged significant risks for pregnant women alongside those with thyroid disorders and liver or kidney dysfunction.
People on thyroid medications: If you’re taking levothyroxine or another thyroid hormone replacement, ashwagandha’s independent thyroid-stimulating effect could create an additive push that tips you into hyperthyroid territory. Dose adjustments should only happen under medical supervision.
People with liver or kidney problems: Impaired organ function could change how the body processes ashwagandha’s active compounds, potentially intensifying its effects.

A safety evaluation specifically recommended restricting ashwagandha’s use as a food additive, enhancing label warnings, and conducting more high-quality studies to clarify its safety thresholds.¹⁰ The endocrinology perspective is similarly guarded, with reviewers expressing concern about adrenal insufficiency alongside thyroid effects and concluding the evidence base simply isn’t strong enough to recommend ashwagandha for long-term thyroid management.³

The Adrenal Connection

Ashwagandha is best known as an “adaptogen,” an herb marketed for helping the body cope with stress. Its most replicated effect is reducing cortisol, the body’s primary stress hormone. But cortisol and thyroid hormones are regulated by overlapping pathways in the brain, and influencing one can alter the other.

The hypothalamic-pituitary-adrenal axis, which governs cortisol, and the hypothalamic-pituitary-thyroid axis share upstream signaling infrastructure. Research on ashwagandha’s hormonal activities suggests its effects stem from modulation of these central pathways rather than direct action on any single gland.⁵ This interconnection means you can’t neatly separate ashwagandha’s stress-relief benefits from its thyroid effects. They’re part of the same chain of hormonal influence.

The concern raised by endocrinologists about adrenal insufficiency comes from this coupling.³ If ashwagandha is dialing down the stress axis to reduce cortisol, sustained use at higher doses could suppress adrenal output. And because the thyroid and adrenal axes are intertwined, adrenal suppression can create downstream changes in how thyroid hormones are converted and used by the body. For someone taking ashwagandha primarily for anxiety or sleep, this is an unintended second-order effect worth knowing about.

Dose and Extract Variability

One complicating factor is that “ashwagandha” isn’t one standardized thing. Supplements vary enormously in how the plant material is processed, which compounds are concentrated, and what dose you actually get per capsule.

The trial that demonstrated thyroid effects used 600 mg per day of a standardized root extract.¹ Walk through a supplement aisle, though, and you’ll find products ranging from 300 mg to 1,500 mg per serving. Some use root-only extracts while others blend root and leaf. Different extraction methods yield different ratios of withanolides, the active compounds believed to drive most of ashwagandha’s biological effects. A high-withanolide extract at a moderate dose could have a stronger thyroid effect than a low-withanolide extract at a higher dose.

This variability makes it difficult to generalize from any single study. Trial participants took a controlled, standardized product. The ashwagandha you buy online or at a health food store may be meaningfully different in potency, even if the label claims a similar dose. This problem exists across the supplement industry, but it’s especially relevant here because the margin between “helpful nudge to thyroid function” and “too much thyroid stimulation” may be narrow.

Practical Monitoring If You Choose to Take It

If you decide to use ashwagandha despite the thyroid considerations, a few steps can reduce your risk. Get a baseline thyroid panel before starting. Knowing your TSH, free T3, and free T4 levels before supplementation gives you and your doctor a reference point. Recheck these labs after six to eight weeks of use, which is the timeframe in which the clinical trial saw significant hormone shifts.¹

Starting at the lower end of commonly used doses, around 300 mg per day of a standardized root extract, is more conservative than jumping straight to 600 mg or more. If you’re already on thyroid medication, don’t adjust your prescription dose on your own in response to ashwagandha. Let your endocrinologist make that call based on lab results.

Pay attention to symptoms. Subtle signs that your thyroid is running too hot include feeling warmer than usual, a resting heart rate that creeps upward, difficulty sleeping despite fatigue, and unintended weight loss. These can develop gradually enough that you don’t connect them to a supplement you started months ago.

Why Your Doctor Might Not Ask About It

Ashwagandha falls into a gap in conventional medicine. Most endocrinologists are aware that certain herbal supplements can affect thyroid labs, but the evidence base is small enough that it doesn’t make it into standard clinical guidelines or medication-interaction checklists. Meanwhile, the supplement industry markets ashwagandha heavily for stress and wellness without prominent warnings about thyroid effects.

The result is a communication problem. You might not mention ashwagandha to your doctor because you think of it as a harmless wellness supplement. Your doctor might not ask because it’s not flagged in their prescribing software. And if your thyroid labs come back abnormal, the supplement may not be the first suspect. The case reports in the literature exist precisely because this scenario played out: patients developed thyroid dysfunction, clinicians went through the usual diagnostic workup, and only eventually traced the problem back to ashwagandha.⁶ Telling any healthcare provider who orders your bloodwork that you take ashwagandha is a small step that can prevent a lot of diagnostic confusion.

1
PubMed. Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial
2
Current Drug Discovery Technologies. Achievements in Hypothyroidism Treatment with Herbal Medicine: A Systematic Review of Randomized Controlled Trials
3
The Journal of Clinical Endocrinology & Metabolism. Thyroid, Diet, and Alternative Approaches
4
PubMed. Changes in thyroid hormone concentrations after administration of ashwagandha root extract to adult male mice
5
PubMed Central. Evaluation of Potential Hormonal Activities of Ashwagandha (Withania somnifera)
6
PubMed Central. Ashwagandha as a Unique Cause of Thyrotoxicosis Presenting With Supraventricular Tachycardia
7
PubMed Central. Painless Thyroiditis by Withania somnifera (Ashwagandha)
8
Phytotherapy Research. Potential Adverse Effects of Ashwagandha: A Critical Review of Preclinical and Clinical Evidence
9
PubMed Central. Safety of 12-Months Administration of Ashwagandha (Withania somnifera) Standardized Root Extract in Healthy Adults: A Prospective, Observational Study
10
PubMed Central. Evaluating the Safety of Ashwagandha as a Food Additive: A Focus on Reproductive, Thyroid, and Immune System Effects