NutriStack
Ashwagandha and Levothyroxine, a caution.
Ashwagandha has been associated with increased thyroid hormone levels and rare thyrotoxicosis reports. When combined with levothyroxine, it may contribute to over-replacement symptoms such as palpitations, tremor, anxiety, heat intolerance, or unintended weight loss. The risk is uncertain but clinically relevant because levothyroxine dosing is intentionally narrow.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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At a glance
- Substances
- Ashwagandha and Levothyroxine
- Pair type
- Caution
- Evidence (highest tier)
- Emerging
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Emerging evidence
Caution
What is happening. Ashwagandha has been associated with increased thyroid hormone levels and rare thyrotoxicosis reports. When combined with levothyroxine, it may contribute to over-replacement symptoms such as palpitations, tremor, anxiety, heat intolerance, or unintended weight loss. The risk is uncertain but clinically relevant because levothyroxine dosing is intentionally narrow.
Mechanism. Human data suggest ashwagandha may alter thyroid indices, possibly by stimulating thyroid hormone production or triggering thyroiditis in susceptible people. Exogenous levothyroxine plus a supplement-driven rise in thyroid hormone effect can push the net state toward thyrotoxicosis.
Recommendation. Avoid starting ashwagandha on your own if you take levothyroxine for thyroid replacement or TSH suppression. If you use it, tell your prescriber and check thyroid labs after starting, stopping, or changing the dose.
Sources (2)
- van der Hooft CS, Hoekstra A, Winter A, de Smet PA. Thyrotoxicosis following the use of ashwagandha. Ned Tijdschr Geneeskd. 2005;149(47):2637-2638. PMID 16355578
- 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. PMID 28829155
Stack Score
How this pair moves the number.
Effect on the composite score
If both Ashwagandha and Levothyroxine are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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