A Case of Severe Overt Hypothyroidism Induced by Long-Term Habitual Gargling with Povidone-Iodine for Over 40 Years.

We herein present a case of severe overt hypothyroidism that developed following habitual gargling with povidone-iodine twice daily for >40 years. The patient showed elevated urinary iodine excretion and negative thyroid autoantibodies (thyroglobulin, thyroid peroxidase, and thyrotropin receptor antibodies). After the discontinuation of gargling, the thyroid function and urinary iodine levels normalized within approximately one month. This is the first reported case in which urinary iodine levels were measured before and after the cessation of povidone-iodine gargling. Our findings provide clinical insights into iodine-induced thyroid dysfunction arising from a widely available antiseptic, offering valuable guidance for clinicians involved in thyroid care.