After being diagnosed with Hashimoto's thyroiditis, treatment decisions should be made based on the size of the thyroid and the presence of symptoms. If the thyroid is relatively small and there are no significant compression symptoms, it is possible to follow up and observe without treatment. If the thyroid is significantly enlarged and there are compression symptoms, thyroid hormone preparations can be used to reduce thyroid swelling. If there is hypothyroidism, it is necessary to use thyroid hormone or levothyroxine for supplementary replacement therapy. In cases of Hashimoto's thyroiditis with hyperthyroidism, short-term treatment should follow the treatment for Graves' disease, using antithyroid treatments such as thioamides or thioureas. (Medications should be used under the guidance of a physician, and self-medication without guidance is strongly discouraged.)