Cytomel T3

Cytomel t 3

Triiodothyronine  (C₁₅H₁₂I₃NO₄₎ also known as T3,  is a type of thyroid hormone. This thyroid hormone is similar to thyroxine but with one less iodine atom per molecule. The major form of thyroid hormone in the blood is thyroxine (T₄). The ratio of T₄  to T₃ released in the blood is roughly 20 to 1. Thyroxine is converted to the active T3 (three to four times more potent than T₄)

Most of the thyroid hormone's circulating in the blood is bound to what is called "transport proteins". Only a very small percent of the circulating hormone is free (unbound) and biologically active, hence measuring concentrations of free thyroid hormones is of great diagnostic value.

When thyroid hormone is bound, it is not active in the body, so the amount of free T₃/T₄ is what is important. For this reason, measuring total thyroxine in the blood can be misleading.

Triiodothyronine (T3) exhibits greater activity and is produced in smaller quantity. It is the most powerful thyroid hormone, and affects almost every process in the body, including body temperature, growth, and heart rate.