Synthroid (Levothyroxine, Levothroid, Levoxyl, Unithroid) acts as a replacement for people whose thyroid gland does not produce enough thyroid hormone. Synthroid 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.Take synthroid tablets by mouth 30-60 minutes before a meal (in the morning on an empty stomach) with a full glass of water.