Hypothyroidism may occur not only with iodine-131 treatment of hyperthyroidism, but also with other treatments (e.g., internal medicine, surgery). Even if a considerable number of patients with hyperthyroidism are not treated, hypothyroidism may occur in the future. Some scholars believe that the appearance of hypothyroidism is a sign of cure for hyperthyroidism, and there is no effective means to prevent hypothyroidism from occurring. Fortunately, compared to hyperthyroidism, hypothyroidism is very easy to treat. It is usually corrected by taking thyroxine. This treatment involves artificially supplementing the thyroxine so that the level of thyroid hormone in the blood quickly returns to normal. The dosage is usually adjusted dynamically according to the results of blood tests for thyroid hormone and TSH levels, and some patients need to take it for the rest of their lives because their thyroid function does not return to normal. Reasonable dosage usually does not produce toxic side effects.