It is natural,
Has all the thyroid hormones our own body makes---T1, t2,
T3, t4, and has calcitonin.
Your body will not become immune to it, like some people do with synthroid.
Drs don't like it, because Big pharma has talked it down because they can not really make any money off of it because it is natural, like they can the synthetic drugs.
Thats all I can think of for now. I have this memory issue because of this thyroid issue.