Unithroid, Synthroid and Levithroid are brand names of levothyroxine, a synthetic form of T4. They are manufactured by different companies and therefore have different names. Cytomel is the brand name for synthetic (man made) T3 or liothyronine. Armour Thyroid is a brand name of natural dessicated thyroid derived from the gland of pigs. It contains natural forms of T4 and T3.