NutriStack
Levothyroxine and Vitamin B7, a caution.
High-dose biotin (>5mg/day) interferes with streptavidin-biotin immunoassays used to measure TSH and free T4. This creates FALSELY NORMAL OR ABNORMAL thyroid tests, not a true drug interaction, but can lead to dangerous mismanagement of levothyroxine dosing.
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
- Levothyroxine and Vitamin B7
- Pair type
- Caution
- Evidence (highest tier)
- Strong
- Source citations
- 4 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. High-dose biotin (>5mg/day) interferes with streptavidin-biotin immunoassays used to measure TSH and free T4. This creates FALSELY NORMAL OR ABNORMAL thyroid tests, not a true drug interaction, but can lead to dangerous mismanagement of levothyroxine dosing.
Mechanism. Biotin competes with biotinylated antibodies in streptavidin-biotin sandwich immunoassays. In competitive assays (TSH), biotin causes falsely LOW results. In sandwich assays (free T4), biotin causes falsely HIGH results, mimicking hyperthyroidism.
Recommendation. Stop biotin supplementation at least 48-72 hours before thyroid function tests. Inform your lab and doctor about biotin use. This is an assay interference issue, not a pharmacological interaction.
Sources (4)
- Katzman BM et al. Prevalence of biotin supplement usage in outpatients and plasma biotin concentrations in patients presenting to the emergency department. Clin Biochem. 2018;60:11-16. PMID 30130526
- 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
- Reininghaus EZ, Platzer M, Kohlhammer-Dohr A et al.. PROVIT: Supplementary Probiotic Treatment and Vitamin B7 in Depression-A Randomized Controlled Trial. Nutrients. 2020. PMID 33171595
- Piquero-Casals J, Saceda-Corralo D, Aladren S et al.. Oral Supplementation with l-Cystine, Serenoa repens, Cucurbita pepo, and Pygeum africanum in Chronic Telogen Effluvium and Androgenetic Alopecia: A Double-Blind, Placebo-Controlled, Randomized Clinical Study. Skin Appendage Disorders. 2025. PMID 39911983
Stack Score
How this pair moves the number.
Effect on the composite score
If both Levothyroxine and Vitamin B7 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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