There are three related thyroid hormones responsible for metabolism – tricodide-thyronine (L-T3), L-thyroxine (L-T4) and thyrotrophic hormone responsible for launching T4 production. Most of natural T3 is not produced directly by your thyroid gland, but rather is converted from the T4 thyroid hormone. Cytomel is a synthetically manufactured liothyronine sodium (T3) which resembles the natural T3 hormone . Cytomel (Liothyronine Sodium, L-T3) has proven to be 4-5 times more biologically active and to take effect more quickly than levothyroxine T4. T3 has a faster onset of action as well as… Read More »