The reason is that these meds are more consistent than either a generic form of levothyroxine or a desiccated thyroid med like
Armour Thyroid. From what I’ve come across, including here on this forum,
Armour Thyroid does seem like a harder med to regulate. And it’s the ‘natural’ aspect that seems to be the biggest issue. I understand this is mostly due to the natural inclusion of T3 hormone - present regardless of whether or not needed and/or occurring in uncontrollable amounts.