T_3 is a thyroid hormone that plays a crucial role in regulating metabolism in the body. It is produced by the thyroid gland and is essential for growth, development, and energy production. T_3 works by influencing how cells use oxygen and convert food into energy, impacting overall bodily functions. T_3 is often measured in conjunction with another thyroid hormone, T_4, to assess thyroid health. An imbalance in T_3 levels can lead to various health issues, including hypothyroidism (low levels) and hyperthyroidism (high levels). Proper thyroid function is vital for maintaining a healthy metabolism and overall well-being.