T3, or triiodothyronine, is a hormone produced by the thyroid gland. It plays a crucial role in regulating metabolism, energy production, and overall growth and development in the body. T3 is derived from the conversion of another hormone called thyroxine (T4) and is more potent than T4, meaning it has a stronger effect on the body's functions. T3 influences various bodily processes, including heart rate, body temperature, and the metabolism of carbohydrates, fats, and proteins. Abnormal levels of T3 can lead to health issues such as hyperthyroidism or hypothyroidism, which can affect energy levels, weight, and overall well-being.