Reverse T3 may be raised at times of acute or chronic stress or illness and can reduce the action of active T3 in the body.
There is controversy about the role of reverse T3 in thyroid illness. Conventional endocrinologists (hormone specialists) generally believe that knowledge of the level of this substance does not influence thyroid treatment decisions. The alternative view however is that reverse T3 is effectively 'antithyroid' - 'standard' T3 is the active thyroid hormone that stimulates the body's energy system (metabolism). Reverse T3 is a mirror image - it goes into cells, and instead of controlling metabolic processes it blocks the effect of T3. In this model, reverse T3 is effectively a hibernation hormone - in times of stress and chronic illness it lowers energy release from the cells - so normal thyroid levels with high reverse T3 may still result in hypothyroidism.