In the same person, hyperthyroidism (hyperthyroidism) followed by hypothyroidism (hypothyroidism) is most commonly caused clinically by excessive destruction of thyroid tissue after oral antithyroid medication, or thyroid surgery, or radioactive iodine treatment in a hyperthyroid patient. It may also be one of two conditions: toxic diffuse goiter or chronic lymphocytic thyroiditis (i.e., Hashimoto’s disease). The mechanism of hyperthyroidism to hypothyroidism due to these two causes is not exactly the same. The focus of this article is on chronic lymphocytic, an autoimmune thyroid disease caused by the body due to immune dysfunction. This disease is not uncommon, and in the early stages of its pathogenesis, about 1/5 of patients show symptoms of hyperthyroidism, such as fear of heat, excessive sweating, excessive eating, good hunger, panic, increased heart rate, fatigue, restlessness, agitation, diarrhea, and weight loss. Chronic lymphocytic thyroiditis has a tendency to naturally develop hypothyroidism. After the onset of hypothyroidism, patients exhibit fear of cold, weakness, unresponsiveness, slower movements, swelling, weight gain, forgetfulness, sleepiness, loss of appetite, and constipation. Many scholars have described that the vast majority of this disease eventually becomes hypothyroidism. The cause of hypothyroidism is the continuous destruction of thyroid tissue by inflammation or the patient is affected by the presence of blocking antibodies in his or her own blood. Hyperthyroidism caused by chronic lymphocytic thyroiditis with mild or less pronounced clinical manifestations should not be treated as aggressively as toxic diffuse goiter. If antithyroid drugs are intended, the dose of the drug should be reduced as appropriate, and the duration of medication should be appropriately shortened. Because the disease may eventually become hypothyroid, early prevention of hypothyroidism due to drug therapy is necessary. As for thyroid surgery and radioactive iodine therapy, they are not suitable for hyperthyroidism caused by chronic lymphocytic thyroiditis. Chronic lymphocytic thyroiditis eventually produces hypothyroidism, which must be treated with long-term thyroid hormone supplementation. Special attention should be paid to the fact that medication should be started in small doses and increased slowly according to the patient’s ability to tolerate it, not in a hurry.