Synthroid Levothyroxine tablets What do levothyroxine tablets do?LEVOTHYROXINE (Levothroid(R), Levoxyl(R), Synthroid(R), Unithroid(R) and others) acts as a replacement for people whose thyroid gland does not produce enough thyroid hormone. Levothyroxine can improve symptoms of thyroid deficiency such as slow speech, lack of energy, weight gain, hair loss, dry thick skin and unusual sensitivity to cold. Levothyroxine also helps to treat a condition called goiter, which is an enlarged thyroid gland. Generic levothyroxine tablets are available.