Liothyronine Sodium is a man-made form of thyroid hormone. T3 is the hormone in your body that regulates how fast your metabolism is. The higher your T3 level is, the more calories you will burn, and the more fat loss potential you will have. T3 is a drug that is prescribed to those with hypothyroidism, but it is commonly used by bodybuilders and recreational lifters who want to reach a level of body fat that would be difficult to achieve without drug assistance.