sorry if this is a stupid question.

What is Levothyroxine sodium to t4(Thyroxine)

-and-

Liothyronine sodium to t3(Triiodothyronine)


since they are all thyroid hormones why do they have different names? is there a chemical called Triiodothyronine you could take thats better than Liothyronine? etc.

thanks