Liothyronine (lye-oh-THYE-roe-neen) T3 Levothyroxine (lee-voe-thye-ROKS-een) T4 Liothyronine is a synthetic form of triiodothyronine (T3) and levothyroxine is a synthetic form of thyroxine (T4). T3 and T4 are hormones that may be given to patients who no longer produce a sufficient amount on their own. They may be prescribed alone or in combination. This may be used to reduce the symptoms of hypothyroidism. It may also be used for other conditions as determined by your doctor.
