TIROS，T3, Triiodothyronine is a thyroid hormone, that greatly affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. This hormone is involved in many cellular functions including the metabolism of carbohydrates, fats and proteins. When an individual is no longer producing enough of this hormone on his own, such as when suffering from hypothyroidism, the metabolism does not function properly. When suffering from hypothyroidism, the individual will find body fat gain to be very common and fat loss becomes extremely difficult. The individual also often experiences a loss of energy and even hair loss in some cases. By supplementing with T3 this provides the body with the thyroid hormone it needs and the problem is solved.