There are advantages and disadvantages to, both, desiccated (so-called "natural" hormones) and synthetic hormones. Synthetic hormones are supposedly identical to the ones your body would make if it could, while the desiccated hormones, such as Armour, NatureThroid, ERFA, etc come from pig thyroid.
Pigs produce much more T3 (which is about 4 times more powerful than T4), than humans do and many of us don't need that much T3, though some do.