T4 (Thyroxine): T4 is a hormone produced by the thyroid gland in the human body. It is also known as thyroxine and plays a crucial role in regulating metabolism and overall body function. T4 is often converted into its more active form, T3 (triiodothyronine), which has a more direct impact on cellular metabolism. Thyroid hormones like T4 are essential for maintaining proper growth, development, and energy levels in the body