Is desiccated thyroid good for hypothyroidism?

Before the broad availability of synthetic levothyroxine (T4) in the 1960s, desiccated thyroid, which is thyroid extract from animals (usually pigs), was the primary treatment for hypothyroidism. There’s a theory that desiccated thyroid may be better for hypothyroidism than synthetic T4 because it contains triiodothyronine (T3) in addition to T4. However, this theory is unfounded. In fact, the ratio of T4:T3 in desiccated thyroid extract is about 4:1, which is much lower than the 14:1 ratio within the human thyroid. The relative excess of T3 from desiccated thyroid can be problematic because it is less stable and can lead to unpredictable thyroid hormone levels. Some clinical research has found that desiccated thyroid resulted in more reports of hyperthyroidism compared to synthetic T4.^[1] Synthetic T4 is recommended by the American Thyroid Association over dessicated thyroid preparations because of the above reasons.