The implications of biotin supplementation on multiple sclerosis, hair loss conditions, and thyroid disorders

Biotin, a water-soluble B-vitamin, is widely used as a dietary supplement for hair, skin, and nail health. High-dose biotin (≥ 300 mg/day) has also been studied as a treatment for progressive multiple sclerosis (MS), although the clinical benefit reported in an initial randomized trial was not confirmed in a larger phase 3 trial, and it is not an approved therapy for MS. However, increasing evidence suggests that biotin supplementation, even at over-the-counter doses of 5-20 mg/day, can interfere with thyroid function tests, leading to potential misdiagnoses of hyperthyroidism and autoimmune thyroid disease. This interference occurs in immunoassays reliant on streptavidin-biotin binding, causing falsely elevated free thyroid hormone levels (T3, T4) and falsely suppressed thyroid-stimulating hormone (TSH), with the extent of interference varying by assay and laboratory platform. In this narrative review of clinical studies and case reports, we found that patients with MS and hair loss pathology, such as alopecia areata (AA), conditions frequently coexisting with thyroid dysfunction, may be vulnerable to misinterpretation of thyroid lab results due to biotin supplementation. Several case reports illustrate patients with MS misdiagnosed with Graves' disease or hyperthyroidism while taking high-dose biotin, with laboratory values normalizing after temporary discontinuation. In AA, no such cases have been reported to date; however, over 40% of AA patients exhibit thyroid autoantibodies and many patients with hair loss use biotin, suggesting a potential, though not yet demonstrated, risk in this population. Given the increasing use of biotin, clinicians must be aware of its impact on laboratory assays and ask patients about biotin use before thyroid function testing. The discontinuation period needed to avoid interference is not uniform and depends on the dose, renal function, and assay used; 24-72 hours is often sufficient for over-the-counter doses, whereas longer intervals may be needed for high-dose therapy. Improved awareness can prevent unnecessary treatments and misdiagnoses in individuals with MS, AA, and other autoimmune conditions. This review integrates neurological and dermatological autoimmune overlap in the context of biotin interference and addresses an underexplored gap in the literature. Further research is needed to examine biotin interference across different laboratory methodologies and patient populations.