NutriStack
Biotin and Levothyroxine, a caution.
Biotin (vitamin B7) does not pharmacologically interact with levothyroxine, but it causes clinically dangerous interference with thyroid laboratory tests used to monitor levothyroxine dosing. Most thyroid immunoassays use biotin-streptavidin technology. Excess biotin produces falsely low TSH and falsely high T3/T4 results in standard assays, which can mimic hyperthyroidism or suggest levothyroxine overdosing, leading to inappropriate dose reductions.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Biotin and Levothyroxine
- Pair type
- Caution
- Evidence (highest tier)
- Strong
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Strong evidence
Caution
What is happening. Biotin (vitamin B7) does not pharmacologically interact with levothyroxine, but it causes clinically dangerous interference with thyroid laboratory tests used to monitor levothyroxine dosing. Most thyroid immunoassays use biotin-streptavidin technology. Excess biotin produces falsely low TSH and falsely high T3/T4 results in standard assays, which can mimic hyperthyroidism or suggest levothyroxine overdosing, leading to inappropriate dose reductions.
Mechanism. Most thyroid immunoassays employ biotin-streptavidin coupling. In sandwich assays (TSH, thyroglobulin), excess biotin competes for streptavidin binding sites, preventing signal complex formation and producing falsely low results. In competitive assays (free T4, free T3), excess biotin displaces labeled analyte, producing falsely high results.
Recommendation. Stop biotin supplementation at least 2-3 days (ideally 5 days for high-dose biotin >5 mg/day) before thyroid function testing. Inform your lab and prescriber about biotin supplement use. Hair/skin/nail supplements commonly contain biotin at 2.5-10 mg, well above the level that causes assay interference. This is a lab interference issue, not a true drug interaction.
Sources (3)
- Li D et al. How biotin induces misleading results in thyroid bioassays: case series. Eur Thyroid J. 2019;8(4):193-197. PMID 31555477
- Piketty ML et al. High-dose biotin therapy leading to false biochemical endocrine profiles: validation of a simple method to overcome biotin interference. Clin Chem Lab Med. 2017;55(6):817-825. PMID 28222020
- Ross DS. Treating hypothyroidism is not always easy: When to treat subclinical hypothyroidism, TSH goals in the elderly, and alternatives to levothyroxine monotherapy. Journal of Internal Medicine. 2022. PMID 34766382
Stack Score
How this pair moves the number.
Effect on the composite score
If both Biotin 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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