Introduction Immune checkpoint inhibitors are associated with immune-mediated thyroid disease and other endocrinopathies. Biotin is an over-the-counter supplement known to interfere with lab assays, including thyroid function tests. Biotin-induced complications with lab monitoring during immunotherapy have not been previously reported. Case report We present a case of a 68-year old woman with hypothyroidism after initiating immune checkpoint blockade therapy and abnormal laboratory monitoring values while concurrently taking biotin supplements. Management & outcome: The patient was initiated on levothyroxine with subsequent dose increases over a period of weeks with resolution of symptoms and normalization of free thyroxine levels. Thyroid stimulating hormone (TSH) levels appeared to remain elevated until biotin supplements were held and levels normalized. Discussion The purpose of this report is to provide the first known incidence of biotin complicating the routine monitoring of immune checkpoint inhibitors with elevated TSH levels and to alert providers to elicit accurate medication histories regarding over-the-counter supplements.