Is Biotin (Vitamin B7) Safe with Levothyroxine?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Stop taking biotin supplements at least 48–72 hours before any thyroid blood tests (TSH, Free T4, Free T3). Inform your healthcare provider if you take biotin regularly. High-dose biotin (5,000–10,000 mcg) used for hair and nail health causes the most significant interference.
Why this interaction occurs
Biotin interferes with biotin-streptavidin immunoassay technology used in most modern TSH and thyroid hormone laboratory tests. High biotin levels cause falsely low TSH and falsely elevated Free T4 and Free T3 results, mimicking hyperthyroidism. This can lead to inappropriate dose reductions of levothyroxine and subsequent under-treatment of hypothyroidism.
Evidence
Evidence level: strong.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 302,514 reports mentioning Levothyroxine. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Levothyroxine + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
Related interactions
All Biotin (Vitamin B7) interactions → · All Levothyroxine interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.