The cause of hyperthyroidism becoming hypothyroidism should be clarified. If it is due to drug overdose, the drug can be stopped or reduced. If it is due to the natural course of the disease, surgery, radioactive iodine treatment, can be treated with drugs. 1. Overdose of drugs for hyperthyroidism: It is necessary to reduce or stop the anti-thyroid drugs, and the thyroid function will gradually return to normal. However, patients should not reduce or stop the medication on their own, and need to go to the hospital to follow the doctor’s advice. 2. Natural course of the disease: that is, early hyperthyroidism and late hypothyroidism, such as Hashimoto’s thyroiditis, can be treated with levothyroxine tablets for a long period of time under the guidance of the doctor. Surgery can be considered for those with compression symptoms and suspected malignancy. 3. Hypothyroidism caused by surgery and radioactive iodine therapy: supplemental levothyroxine can be administered under doctor’s supervision. The goal of the treatment is to restore serum thyrotropin and thyroxine levels to the normal range, and lifelong medication is required. Therefore, for hyperthyroidism to become hypothyroidism, it should be clear which cause is responsible for it, and different measures should be taken for different causes. Patients with hyperthyroidism must go to the hospital for regular checkups during treatment, and doctors will adjust the medication regimen according to the patient’s condition to avoid hypothyroidism. If hypothyroidism occurs, the treatment should be carried out under the guidance of the doctor, and should not stop or reduce the medication on its own.