T3 is the Main Active Tthyroid Hormone
I have said many times that T4 is a prohormone or storage hormone and that T3 is the only truly active thyroid hormone. I remain of this view.
However, from time to time someone airs an opinion that everyone needs to take some T4 (Levothyroxine, Synthroid or NDT).
So, in this blog post I want to make it very clear what I mean by 'T3 being the only truly active thyroid hormone'.
Genomic and non-genomic action of thyroid hormones