Thyroid conditions are not simple to treat and much of the abundant information (a keyword search on “hypothyroid” produces more than 2.5 million results) is contradictory.
At the heart of the issue are two categories of thyroid hormone replacement drugs. The older form of treatment called “dessicated thyroid” is a preparation of dried and powdered porcine thyroid glands. This preparation has been in use since the 19th century to replace thyroid hormones T1, T2, T3 and T4 and calcitonin.
In the 1950s a synthetic hormone, called levothyroxine or “synthetic T4,” was introduced by pharmaceutical companies. Though it has gained market share, it does not always restore people to lives without symptoms.
For a variety of perspectives on thyroid treatments, start with these resources: