Biotin itself is low-risk
Biotin (vitamin B7) supports metabolism. The NIH Office of Dietary Supplements lists an adult Adequate Intake of 30 mcg/day, and no Tolerable Upper Intake Level because biotin has not been shown to be toxic at high intakes [1]. Deficiency is uncommon. The catch isn't biotin's safety — it's what high doses do to lab tests.
How biotin distorts blood tests
Many lab tests use a biotin-streptavidin binding system. When someone takes high-dose biotin (often 5,000–10,000 mcg in 'hair, skin, and nails' products), the extra biotin can interfere with these assays and produce falsely high or falsely low results [1]. Documented examples include [1]:
- Thyroid tests that mimic an overactive thyroid
- Falsely altered hormone results
- A falsely low troponin result — the marker used to diagnose a heart attack — which in at least one case contributed to a missed diagnosis and a patient death
The FDA warning
NIH cites the FDA's safety communication advising providers to ask patients about biotin and to consider biotin interference when lab results don't match the clinical picture [1][2]. The doses involved are common in beauty supplements, so this is a real-world issue, not a rare edge case.
Practical guidance
- Tell your provider and the lab about any biotin you take, including multivitamins and beauty products — see [supplements and lab-test interference](/learn/supplements-lab-test-interference).
- Pause biotin before testing if your clinician advises it; some labs suggest stopping it for a couple of days before certain tests.
- Be skeptical of mega-dose biotin for hair and nails — the evidence for benefit in people who aren't deficient is limited, while the lab-interference risk is well documented.