Non-thyroidal illness syndrome is a manifestation of hypothalamic-pituitary dysfunction, and in view of current evidence, should be treated with appropriate replacement therapies.

This article documents the role of hypothalamic hypothyroidism and decreased T4-->T3 conversion as the cause of low T4 and T3 in non-thyroidal illness syndrome (NTIS). This article also presents the arguments for administration of replacement triiodothyronine (T3) and thyroxine (T4) hormone in patients who have NTIS. It is impossible to be certain at this time that it is beneficial to replace hormone, or whether this could be harmful. Only a prospective study will be adequate to prove this point, and probably this would need to involve hundreds of patients. If effective, thyroid hormone replacement will be one of many beneficial treatments given the patient, rather than a single magic bullet, which would reverse all the metabolic changes going wrong in these severely ill patients.