Levothyroxine, also called L-thyroxine, is a synthetic form of thyroxine (
thyroid hormone). In the United States, brand names include Synthroid, Levoxyl, Levothroid, Eltroxin, Tirosint and Unithroid; Generic forms are Levothyroxine sodium USP and L-thyroxine. There is still debate over whether generic thyroid supplements are as effective as thyroid brand name supplements.