Thyroid hormones are used as replacement therapy when the patient is hypothyroid. By supplementing the decreased endogenous thyroid production and secretion with exogenous thyroid hormones, an attempt is made to create a euthyroid (normal thyroid) state. Levothyroxine (Synthroid) is the drug of choice for hypothyroidism because it is relatively inexpensive, requires once-a-day dosages, and has a more uniform potency than do other thyroid hormone replacement drugs.
Myxedema is a severe hypothyroidism manifested by lethargy, apathy, memory impairment, emotional changes, slow speech, deep coarse voice, thick dry skin, cold intolerance, slow pulse, constipation, weight gain, and absence of menses.
Thyroid hormones are also used in the treatment or prevention of various types of euthyroid goiters (enlargement of the thyroid gland), including thyroid nodules, subacute or chronic lymphocytic thyroiditis (Hashimoto's), and multinodular goiter and in the management of thyroid cancer. The hormone may be used with the antithyroid drugs to treat thyrotoxicosis. Thyroid hormones also may be used as a diagnostic measure to differentiate suspected hyperthyroidism from euthyroidism.
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