The short answer
Biotin can distort some thyroid blood tests without changing thyroid hormone levels in the body. The cited U.S. levothyroxine labeling specifies stopping biotin for at least two days before TSH or T4 testing, but the required hold may be longer depending on dose, kidney function and test method.
What this answer covers
Applies to affected thyroid immunoassays regardless of how levothyroxine is administered; it is a test-interference issue.
- Supplement or preparation
- Biotin
- Medication ingredient
- levothyroxine
Evidence and practical considerations
Timing & monitoring
Mechanistic, in-vivo, laboratory-guidance, and regulatory evidence strongly support a pretest hold. The exact duration must be assay- and dose-aware, with at least two days as the current U.S. label minimum.
- Exact scope
- biotin with levothyroxine
- Medication form and route
- all levothyroxine routes when dosing is monitored with affected thyroid immunoassays
- Timing or duration
- Hold interval depends on biotin dose, assay, renal clearance, and manufacturer; current U.S. levothyroxine labeling specifies at least two days for TSH/T4 assessment.
What remains uncertain
- Official recommendations range from at least two days to three days or one week.
- The U.S. label's two-day minimum is not a guarantee for high-dose therapy, renal impairment, or every assay.
- Biotin does not change thyroid hormone biologically; it changes selected test results.
Factors that may matter: biotin dose; time since last dose; renal impairment; assay platform; analyte; thyroid cancer or other narrow monitoring target.
Read the supporting source summaries
Source 1: current U.S. regulatory product labeling
dailymed.nlm.nih.gov · Source check Jul 24, 2026
Population: Patients monitored with TSH or thyroid-hormone immunoassays while taking levothyroxine.
Instructs patients to stop biotin and biotin-containing supplements for at least two days before assessing TSH or T4.
Two days may not cover very high doses, renal impairment, or highly sensitive assay platforms.
Source 2: laboratory-medicine professional guidance
academic.oup.com · Source check Jul 24, 2026
Population: Patients using 5 mg to 300 mg biotin and laboratories using biotinylated immunoassays.
Confirms dose-, platform-, and renal-function-dependent interference; 5 to 10 mg may clear for some assays within hours, whereas high doses can require days.
No universal washout covers all assays; manufacturers update thresholds.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Research summary published |
Article revision: f625f9b1d8d551ee
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
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Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.