Someone please explain what T3 does vs. T4
I am learning so much about thyroid disease, but one thing I'm not clear on is the role of T3 vs. T4. I have heard that T4 is the actual working hormone, and that T3 converts to T4. Is that correct? If so, why would one need to be treated with both T4 (like synthroid) and T3 (like cytomel)?
When I took cytomel in 2003 (without any T4), it ended up pushing my T4 down below the normal range. When the endo took me off, the T4 went into normal. It is now very low normal (free T4 = .82) and TSH is now out of range (3.130).
Thanking you all for your expert guidance.