T3 IS ONE OF THE TWO MAJOR HORMONES PRODUCED BY THE THYROID GLAND AND THE OTHER ONE IS CALLED T4 OR THYROXINE. T3 PLAYS AN IMPORTANT ROLE IN YOUR BODY'S METABOLISM OR T4 IS THE MAJOR THYROID HORMONE PRODUCED BY THE THYROID GLAND AND IS CHEMICALLY CONVERTED TO T3 WHICH T3 HELPS CONTROL MANY BODY FUNCTIONS INCLUDING GROWTH, BODY TEMPERATURE AND HEART RATE. USUALLY T3 TOTAL IS ELEVATED IN HYPERTHYROIDISM, LOWERED IN HYPOTHYROIDISM.