Does biotin interact with thyroid function or thyroid medications like levothyroxine (thyroid hormone replacement therapy)?

Biotin and Thyroid Function Interactions

Biotin can significantly interfere with thyroid function tests, causing falsely abnormal results that may lead to misdiagnosis and inappropriate treatment, but does not directly interact with thyroid function or levothyroxine medication. 1, 2, 3

Biotin's Impact on Thyroid Testing

Laboratory Interference

• Biotin supplements, even at over-the-counter doses, can cause significant interference with common immunoassays used to measure thyroid hormones 1
• This interference occurs because biotin is used as a component in standard immunoassays that detect serum levels of various hormones including TSH and thyroxine 2
• The biotin-streptavidin interaction in these assays is disrupted by exogenous biotin, causing falsely lowered TSH and falsely elevated T4 readings that can mimic hyperthyroidism or Graves' disease 3

Magnitude and Duration of Interference

• A daily dose of just 10 mg biotin has been shown to interfere with specific assays for TSH, free T4, total T3, and thyroglobulin 4
• Maximum biotin interference occurs approximately two hours after biotin ingestion 4
• The interference can affect multiple thyroid parameters simultaneously, creating a biochemical picture that falsely suggests thyroid dysfunction 2, 3

Clinical Implications

Misdiagnosis Risk

• Patients taking biotin supplements may receive erroneous thyroid diagnoses if their clinicians are unaware of this interference 1
• This is particularly problematic for patients with existing thyroid conditions who require careful monitoring and medication adjustment 4
• Patients on immunotherapy or other treatments that can cause true thyroid dysfunction may have their monitoring complicated by concurrent biotin use 5

Management Recommendations

• Clinicians should carefully question patients about biotin supplement use before ordering thyroid function tests 1
• Patients should be advised to discontinue biotin supplementation for at least 1 week before thyroid function testing 2
• When clinical presentation does not match laboratory results, biotin interference should be considered as a potential cause 3

Biotin and Levothyroxine

Direct Medication Interactions

• There is no evidence of a direct interaction between biotin and levothyroxine absorption or metabolism 6
• Unlike bile acid sequestrants such as cholestyramine or colestipol, which can bind to levothyroxine and reduce its absorption, biotin does not have this effect 6

Monitoring Considerations

• For patients on levothyroxine therapy, biotin interference can lead to inappropriate dose adjustments if the laboratory interference is not recognized 4
• Multiple TSH tests should be performed over a 3-6 month interval to confirm abnormal findings, especially when biotin use may be present 7
• The high variability of TSH secretion levels underscores the importance of not relying on a single abnormal laboratory value for adjusting levothyroxine dosage 6, 7

Safety of Biotin

• Biotin toxicity is unlikely even at high doses; no upper limit has been established 6
• No adverse effects have been shown for both oral and IV administration of pharmacological doses of biotin up to 5 mg/day for prolonged periods 6
• The clinical concern with biotin is not direct toxicity but rather its potential to interfere with accurate laboratory assessment 1, 2

Practical Recommendations

• Advise patients to disclose all supplements, including biotin, during medical visits 1
• For patients requiring thyroid function testing, recommend discontinuing biotin supplements at least 7 days before the blood draw 2, 3
• When unexpected thyroid test results are encountered, consider biotin interference, especially if the clinical picture does not match laboratory findings 3
• Communicate with the laboratory when biotin interference is suspected to determine if alternative testing methods can be used 2