Triiodothyronine, often abbreviated as T3, is a hormone produced by the thyroid gland. It plays a crucial role in regulating metabolism, influencing how the body uses energy. T3 affects various bodily functions, including heart rate, temperature regulation, and growth. T3 is derived from another hormone called thyroxine or T4, which is converted into T3 in the body. Proper levels of T3 are essential for maintaining overall health, and imbalances can lead to conditions such as hyperthyroidism or hypothyroidism, affecting energy levels and overall well-being.