Levothyroxine is the synthetic version of thyroxine, which
is produced by the body.
Levothyroxine is identical
to thyroxine.
You could always try a desiccated type of hormones. They're produced from pig thyroid, such as Armour. It contains, both T4 and T3. Although pigs produce more T3 than humans, many people do very well on desiccated hormones. I took them for a while but insurance didn't cover them, so again, they because quite expensive for me.