Effects of Thyroxine as Compared with Thyroxine plus Triiodothyronine in Patients with Hypothyroidism

There are two thyroid hormones, thyroxine and triiodothyronine. The daily production of thyroxine is about 100 μg, all produced by the thyroid gland. The daily production of triiodothyronine is about 30 μg, of which about 20 percent is produced by the thyroid gland and 80 percent by deiodination of thyroxine in extrathyroidal tissues. 1 Not all tissues that need thyroid hormone are equally able to convert thyroxine to triiodothyronine, the active form of the hormone. 2 Nevertheless, most patients with hypothyroidism are treated only with thyroxine (levothyroxine). Although this treatment is effective, some patients with hypothyroidism treated with thyroxine are not entirely . . .