Warning: Biotin, a popular nail supplement, may interfere with lab tests for heart attacks and thyroid function. Before you reach for that supplement bottle of biotin, make sure you know about this recent FDA warning. Biotin may interfere with laboratory tests, including tests for heart attacks and thyroid function. Biotin supplements have become popular for those with brittle nails, but are the subject of a recent FDA warning Biotin is a popular supplement for nail health, b