Biotin (Vitamin B7)
Biotin (vitamin B7) is a water-soluble vitamin used in many cosmetic supplements for hair and nail growth.
Relevance to Thyroid Testing
High-dose biotin supplements (commonly sold at 5,000–10,000 mcg — far above the 30 mcg adult daily requirement) can interfere with immunoassay-based thyroid blood tests, producing false readings:
- Falsely abnormal TSH, FT4, or FT3 levels
- May mimic a pattern suggesting hyperthyroidism
The american-thyroid-association advises stopping biotin supplements for at least 2 days before thyroid function blood tests.
No clear evidence exists that biotin benefits thyroid conditions directly.