The reason for taking t4 with gh is that gh upregulates the conversion of t4 to t3.

T4 is produced by the thyroid.
The petitutary produces TSH (thyroid stimulating hormone) which converts t4 to t3.
T3 is what the body uses for metabolism.
This is how the body self regulates.

T4 does nothing for us. T3 does. Gh UPCONVERTS t4 to t3. MORE t4 means more converstion to t3. Taking t4 orally does not shut down your thyroid. Taking t3 orally shuts down your thyroid. Taking t4 with gh lets your petitutary and thyroid relax a little and keeps t3 maximal. Taking t3 with gh shuts down thyroid and removes the conversion process completely, which does nothing for us and if you come off gh and/or t3, you have to wait for your thyroid to bounce back. Taking t4 you dont have a bounce back because the thyroid never shuts down.