Reverse T3 (rT3) Unit Converter

Reverse T3 (rT3) is an inactive form of thyroid hormone produced when your body converts thyroxine (T4) through a process called inner ring deiodination.

While about one-third of T4 normally converts to the active hormone T3, another portion converts to rT3. Unlike T3, which actively supports metabolism and energy production, rT3 is biologically inactive and binds weakly to thyroid hormone receptors.

Reverse T3 essentially acts as a metabolic brake, and its levels can shift when the body needs to conserve energy during illness, stress, or caloric restriction.

Reverse T3 is primarily produced in peripheral tissues, especially the liver and kidneys, through enzymatic conversion of T4 by type 1 and type 3 deiodinase enzymes. A small amount is also secreted directly by the thyroid gland.